TECHNICAL FIELD

[0001] The present invention relates to the field of voltage sensors, and more particularly to optical voltage sensors for alternating current applications.

BACKGROUND

[0002] Over the past few years, power systems (generation, transmission, and distribution) have undergone several major technological developments with optimized control as their ultimate aim. These developments rely on a better understanding of power system dynamics and inevitably require more instrumentation. In this context, it is important to minimize the electrical, mechanical and environmental impacts of new instrumentation, which must also meet particular reliability and precision requirements as well as isolation standards for each voltage level.

[0003] Generally speaking, current and voltage are the two primary inputs for all electrical parameter measurements. Measuring current is normally quite straightforward and meets the conditions mentioned above. Several sensors are available that do not even require an open circuit. In addition to a wide measurement range, excellent precision and a high degree of electrical isolation, these sensors are also robust and can be installed on a power system with no major service continuity impacts.

[0004] However, the same cannot be said of voltage measurement, which generally requires the use of measurement transformers connected in parallel with the line(s) forming the system. From a mechanical point of view, these voltage transformers are relatively heavy and their installation requires certain precautions. In addition, installing them on medium or high- voltage systems sometimes requires the use of a bypass disconnect switch so they can be isolated in case of malfunction.

[0005] To overcome those deficiencies, some optical voltage sensors comprising a floating conductor placed in galvanic isolation to the electrical cable for which the measurement of the voltage is required and a light source have been developed. The light source is connected to the electrical cable and the floating conductor. A movement of charges between the electrical cable and the floating conductor generates a current that powers the light source and the light signal emitted by the light source is representative of the voltage of the electrical cable. Other optical voltage sensors comprise two floating conductors placed in galvanic isolation to the electrical cable at different distances from the electrical cable and a light source is connected between the two floating conductors. The movement of charges between the two floating conductors generates a current that powers the light source and the light signal emitted by the light source is representative of the voltage of the electrical cable. Further optical voltage sensors comprise a conducting device placed in galvanic isolation to the electrical cable and a light source connected to the conducting device and the ground. The movement of charges between the conducting device and the ground generates a current that powers the light source and the light signal emitted by the light source is representative of the voltage of the electrical cable.

[0006] While providing some advantages, such optical voltage sensors present a maximal precision of about 0.5% which may not be sufficient for some applications. Furthermore, such optical voltage sensors offer a limited bandwidth.

[0007] Therefore, there is a need for an improved optical sensor for voltage measurement.

SUMMARY

[0008] According to a broad aspect, there is provided a voltage sensor assembly for obtaining a light signal representative of an AC voltage in a powered conductor, comprising: a first conductor adapted to be placed spaced apart from the powered conductor within the electrical field of the powered conductor and in galvanic isolation to the powered conductor; a light source for emitting the light signal, the light source having a first terminal connected to the first conductor and a second terminal connectable to a second conductor, the first and second conductors being at different electrical potentials, a connection of the second terminal to the second conductor causing a movement of electric charges between the first and second conductors and extracting a given AC current from the movement of electric charges, the light source being powered by the given AC current, and an intensity of the light signal being indicative of a value of the AC voltage in the powered conductor; an optical waveguide operatively coupled to the light source for collecting and propagating over a distance at least a portion of the light signal emitted by the light source; and a current source for generating an electrical current, the electrical current source being electrically connected to the light source for delivering the electrical current to the light source.

[0009] In one embodiment, the second conductor corresponds to the powered conductor, the second terminal of the light source being connectable to the powered conductor.

[0010] In another embodiment, the voltage sensor assembly further comprises the second conductor, the second terminal being connected to the second conductor.

[0011] In a further embodiment, the second conductor is a grounded element.

[0012] In one embodiment, the current source is adapted to deliver at least one of a

DC electrical current and an AC current.

[0013] In one embodiment, the light source is a light emitting diode (LED).

[0014] In one embodiment, the electrical current is chosen so as to substantially constantly operate the LED in a conduction state in which light is emitted.

[0015] In one embodiment, the current source comprises a current supply electrically connected to the light source and a battery electrically connected to the current supply for powering the current supply.

[0016] In one embodiment, the battery is rechargeable.

[0017] In one embodiment, the voltage sensor assembly further comprises an electromagnetic induction power generator for one of charging the battery and powering the current supply, the electromagnetic induction power generator converting an electromagnetic field generated by the powered conductor into electricity. [0018] In one embodiment, the voltage sensor assembly further comprises a rectifier electrically connected between the electromagnetic induction power generator and the rechargeable battery.

[0019] In one embodiment, the voltage sensor assembly further comprises a conducting element and a main transformer, the conducting element being adapted to be placed spaced apart from the powered conductor and being in galvanic isolation to the floating conductor and the powered conductor, the main transformer being electrically connected to the conducting element and electrically connectable to the powered conductor for one of charging the battery and powering the current supply when the main transformer is connected to the powered conductor.

[0020] In one embodiment, the voltage sensor assembly further comprises a rectifier electrically connected between the main transformer and the rechargeable battery.

[0021] In one embodiment, the current source comprises a current supply and an electromagnetic induction power generator for powering the current supply, the electromagnetic induction power generator converting an electromagnetic field generated by the powered conductor into electricity.

[0022] In one embodiment, the voltage sensor assembly further comprises a rectifier electrically connected between the electromagnetic induction power generator and the current supply.

[0023] In one embodiment, the current source comprises a current supply, a conducting element and a main transformer electrically connected to the current supply, the conducting element being adapted to be placed spaced apart from the powered conductor and being in galvanic isolation to the floating conductor and the powered conductor, the main transformer being electrically connected to the conducting element and electrically connectable to the powered conductor for powering the current supply when the main transformer is connected to the powered conductor.. [0024] In one embodiment, the voltage sensor assembly further comprises a rectifier electrically connected between the main transformer and the current supply.

[0025] According to another broad aspect, there is provided a method for obtaining a light signal representative of an AC voltage in an powered conductor, comprising: placing a first conductor spaced apart from the powered conductor within the electrical field of the powered conductor and in galvanic isolation to the powered conductor; connecting a current source to a light source, thereby delivering an electrical current to the light source; electrically connecting a first terminal of the light source to the first conductor and a second terminal of the light source to a second conductor being at an electrical potential different from an electrical potential of the first conductor, thereby causing a movement of electric charges between the first and second conductors and extracting a given AC current from the movement of electric charges, the light source being powered by the given AC current, and an intensity of the light signal being indicative of a value of the AC voltage in the powered conductor; emitting a light signal from the light source as a result of the given AC current and the electrical current powering the light source, an intensity of the light signal being indicative of a value of the AC voltage in the electrical conductor; optically coupling at least a portion of the light signal into an optical waveguide; and propagating the coupled light signal over a distance in the optical waveguide.

[0026] In one embodiment, the step of electrically connecting the second terminal of the light source to the second conductor comprises electrically connecting the second terminal of the light source to the powered conductor.

[0027] In one embodiment, the method further comprises placing the second conductor spaced apart from the powered conductor within the electrical field of the powered conductor and in galvanic isolation to the powered conductor.

[0028] In one embodiment, the step of electrically connecting the second terminal of the light source to the second conductor comprises electrically connecting the second terminal of the light source to a ground. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Further features and advantages of the present invention will become apparent from the following detailed description, taken in combination with the appended drawings, in which:

[0030] Figure 1 is a block diagram schematically illustrating an optical voltage sensor comprising at least one conducting device, a light source and a current source, in accordance with an embodiment;

[0031] Figure 2 is a block diagram schematically illustrating an optical voltage sensor comprising a floating conductor, a light source and a current source, the light source being connected to the floating conductor and connectable a powered cable, in accordance with an embodiment;

[0032] Figure 3 illustrates an optical voltage sensor comprising a floating conductor, a light source and a current source, the light source being connected to the floating conductor and connectable a powered cable, and the floating conductor having a cylindrical shape, in accordance with an embodiment;

[0033] Figure 4 illustrates an optical voltage sensor comprising a floating conductor, a light source and a current source, the light source being connected to the floating conductor and connectable a powered cable, and the optical voltage sensor comprising two hemi-cylindrical portions adapted to clamp over a powered conductor, in accordance with an embodiment;

[0034] Figure 5 illustrates an optical voltage sensor comprising two cylindrical floating conductors each in the shape of a cylinder, a light source and a current source, the light source being connected to one of the two floating conductors and connectable to a powered cable, a transformer being connected to the other floating conductor and connectable to the powered cable, in accordance with an embodiment;

[0035] Figure 6 illustrates a voltage sensing system comprising three voltage sensors each securable to a respective bundle conductor of a high power line, each voltage sensor comprising a substantially cylindrical casing formed of four curved plates, in accordance with an embodiment;

[0036] Figure 7 illustrates a voltage sensing system comprising three voltage sensors each securable to a respective bundle conductor of a high power line, each voltage sensor comprising a substantially cylindrical casing formed of two planar or flat plates and two curved plates, in accordance with an embodiment;

[0037] Figure 8 illustrates a voltage sensing system comprising two voltage sensors each securable to a respective ground conductor of a high power line, in accordance with an embodiment; and

[0038] Figure 9 is a block diagram schematically illustrating a contactless optical voltage sensor comprising a conducting device, a light source and a current source, the light source being connected to the conducting device and connectable to the ground, in accordance with an embodiment;

[0039] Figure 10 is a block diagram schematically illustrating a contactless optical voltage sensor comprising two floating conductors, a light source and a current source, the light source being electrically connected between the two floating conductors, in accordance with an embodiment;

[0040] Figures 11A and 11B show a Faraday cage example embodiment with two concentric cylindrical floating conductors in open (Figure 8 A) and closed (Figure 8B) clamping configurations, in accordance with an embodiment;

[0041] Figure 12 shows a conducting element example embodiment with a single grounded conductive cylinder, in accordance with an embodiment;

[0042] Figure 13 shows a conducting element example embodiment with a single grounded conductive cylinder, in which a dielectric material is present between the conductive cylinder and the electrical wire; and [0043] Figure 14 shows a conductive plate example embodiment in which the sensor housing is shaped to allow the conductive plate to be positioned in close proximity to the electrical wire.

[0044] It will be noted that throughout the appended drawings, like features are identified by like reference numerals.

DETAILED DESCRIPTION

[0045] There is described a voltage sensor assembly for obtaining a light signal indicative of the Alternating Current (AC) voltage of a powered conductor. The voltage sensor assembly comprises at least one conducting device, at least one light source electrically connected to the conducting device and an optical waveguide for collecting and propagating over a distance at least part of the light generated by the light source. The voltage sensor assembly further comprises a source of current which may be a source of Direct Current (DC) current and/or a source of AC current.

[0046] The conducting device is adapted to be positioned spaced apart from the powered conductor and in galvanic isolation to the powered conductor while being located within the electric field of the powered conductor. A movement of charges occurring within the voltage sensor assembly, as described below, creates an AC current that powers the light source which in turns emits light. The intensity of the light emitted by the light source due to the AC current is indicative of the value of the current flowing through the light source which is indicative of the value of the AC voltage in the powered conductor.

[0047] In one embodiment, the voltage sensor assembly comprises a single conducting device which is in galvanic isolation to the powered conductor, the ground and any other conducting element. The conducting device is then referred to as a floating conductor. In this case, the light source has a first terminal electrically connected to the floating conductor and a second terminal electrically connectable to the powered conductor. When the light source is connected to the powered conductor, a movement of charges occurs between the powered conductor and the floating conductor, which creates an AC current that powers the light source. [0048] In another embodiment, the voltage sensor assembly comprises two conducting devices which are each in galvanic isolation to the powered conductor, the ground and any other conducting element including the other conducting device. These two conducting devices are then referred to as floating conductors. The two floating conductors are placed at different distances from the powered conductor within the electric field of the powered conductor so as to be at different electrical potentials. The light source has a first terminal electrically connected to the first floating conductor and a second terminal electrically connected to the second floating conductor. The difference of electrical potentials between the two floating conductors creates a movement of charges between the two floating conductors which generates an AC current that powers the light source.

[0049] In a further embodiment, the voltage sensor assembly comprises a single conducting device which is in galvanic isolation to the powered conductor and located within the electric field of the powered conductor. The light source has a first terminal electrically connected to the conducting device and a second terminal electrically connectable to the ground. The second terminal may be electrically connected to any grounded device or element. For example, the second terminal may be connected to an electrical wire or cable connected to the ground. Upon connection of the light source to the ground, a movement of charges occurs between the conducting device and the ground which generates an AC current that powers the light source.

[0050] The current source is electrically connected in parallel to the light source so that the electrical current delivered by the current source be used for powering the light source in addition to the AC current created by the above-described movement of charges. As a result, the current flowing through the light source comprises a first component from the current source and a second AC component created by the movement of charges. Since it is related to the current delivered by the current source, the intensity of the light emitted by the light source due to the current delivered by the current source acts as a reference signal.

[0051] In one embodiment, the light source is a light emitting diode (LED). In this case, the present voltage sensor assembly can also be used to measure the phase of the voltage, as long as the light source has a fast enough response time to temporally resolve the signal with a few harmonics, a condition easily met with an LED.

[0052] In another embodiment, the light source is a laser.

[0053] In one embodiment, the light source is a micro-light source such as a micro-

LED or a micro-laser.

[0054] The optical waveguide used for collecting the light emitted by the light source is optically connected to a read-out unit. The optical waveguide may be a glass or polymer optical fiber, which could also be sheathed with highly effective insulating material. The material used can have a breakdown voltage greater than that of air. This high degree of electrical isolation and breakdown resistance could be an even greater advantage at medium or even high voltages.

[0055] In applications where the powered conductor is not covered by an insulating sheath, the conducting device or floating conductor(s) can include an insulation layer to ensure that there is no galvanic contact with the powered conductor.

[0056] Figure 1 schematically illustrates one embodiment of a voltage sensor assembly 100 for measuring the AC voltage of a powered electrical conductor 102 such as a medium or high voltage cable. The voltage sensor assembly 100 comprises a voltage sensor subassembly 104 and a current source 106. The voltage sensor subassembly 104 comprises an LED 108, at least one conducting device 110 and an optical waveguide 112 for collecting light emitted by the LED and propagating the collected light up to a read-out unit 114. The conducting device 110 is positioned adjacent to the electrical conductor 102 while being spaced apart from the powered conductor 102 so as to be in galvanic isolation to the powered conductor 102.

[0057] The current source 106 is connected in parallel to the LED 108 for generating a DC current to power the LED 108 which is then polarized by the DC current.

[0058] In one embodiment, the voltage sensor assembly 100 comprises a single conducting device 110 which corresponds to a floating conductor and the LED 108 has a first terminal connected to the floating conductor 110. The second terminal of the LED 108 is connectable to the powered conductor 102. Upon connection of the LED 108 to the powered conductor 102, a movement of charges occurs between the powered conductor 102 and the floating conductor 110, which creates an AC current that flow through the LED 108 and powers the LED 108.

[0059] In another embodiment, the voltage sensor assembly 100 comprises a single conducting device 110 which corresponds to a floating conductor. The LED 108 has a first terminal connected to the floating conductor 110. The second terminal of the LED 108 is connectable to the ground. Upon connection of the LED 108 to the ground, a movement of charges occurs between the powered conductor 102 and the ground, which creates an AC current that flow through the LED 108 and powers the LED 108.

[0060] In a further embodiment, the voltage sensor assembly 100 comprises two floating conductors 110 which are located at different distances from the powered conductor 102 while being in galvanic isolation to the powered conductor 102 and located within the electric field of the powered conductor. As a result of the different distances between the floating conductors 110 and the powered conductor 102, the two floating conductors are at different electrical potentials. The LED 108 has a first terminal electrically connected to the first floating conductor 110 and a second terminal electrically connected to the second floating conductor 110. As a result of the different electrical potentials between the two floating conductors 110, a movement of charges occurs between the two floating conductors 110, which creates an AC current that flow through the LED 108 and powers the LED 108.

[0061] As a result, the current flowing through the LED 108 comprises two components: an AC component generated by the above-described movement of charges and a DC component generated by the current source 106. The AC current component is indicative of the AC voltage of the powered conductor 102.

[0062] As a result of the AC and DC currents flowing through the LED 108, the

LED 108 emits light which also has both a DC component and an AC component. The DC component of the emitted light corresponds to the amount of light emitted by the LED 108 due to the DC current while the AC component of the emitted light corresponds to the amount of light emitted by the LED 108 due to the AC current. Since the AC current is indicative of the AC voltage in the powered conductor 102, the AC component of the light emitted by the LED 108 is also indicative of the AC voltage of the powered conductor 102. As a result, the amplitude, intensity or power of the light emitted by the LED 108 is also indicative of the AC voltage of the powered conductor 102.

[0063] While a floating conductor is no longer considered as being "floating" as soon as it is connected to the ground, such a conductor will still be called a floating conductor even after its connection to the ground for the purpose of the present description.

[0064] The optical waveguide 112 collects at least part of the light emitted by the

LED 108 and propagates the collected along its length up to a read-out unit 114. The readout unit 114 detects the incoming light and measure its amplitude, intensity or power in time and determines the voltage in time of the powered conductor 102.

[0065] In one embodiment, the value of the DC current is chosen so as to substantially constantly operate the LED 104 in direct conduction, i.e. the value of the DC current applied to the LED is equal to or greater than the peak value of the AC current. In this case, the value of the DC current coming from the current source 106 is substantially constant in time and corresponds to a reference value. The AC current is proportional to the derivative of the AC voltage of the electrical conductor 102. The ratio between the AC current and the DC current is then also proportional to the derivative of the AC voltage of the electrical conductor 102 since the DC current is substantially constant. The light emitted by the LED 108 then comprises an AC component, i.e. the amount of light emitted due to the AC current applied to the LED 108, and a DC component, i.e. the amount of light emitted due to the DC current applied to the LED 108. If the LED 108 is operated in a substantially linear regime, the ratio between the AC and DC components of the emitted light is also proportional to the derivative of the AC voltage of the electrical conductor 102. [0066] In one embodiment, the ratio between the AC and DC components of the emitted light is substantially constant in time even if a linear variation of the property of a component occurs in time. For example, the linear variation in time of the efficiency of the LED 108 or the response of the LED 108 may not affect the ratio between the AC and DC components of the emitted light. Other examples of linear variations in time that may not impact the ratio between the AC and DC components of the emitted light may include the linear variation of the coupling ratio between the LED 108 and the optical waveguide 112, the linear variation of the gain to the electrical circuit for treating the data, or the like.

[0067] In an embodiment in which the DC current intensity is superior to the peak intensity of the AC current, a single LED 108 may be used and therefore a single optical waveguide 112 and a single optical detection circuit may be used. In this case, the LED 108 is operated in conduction which allows the read-out unit 114 to generate, upon detection of the light, an electrical detection signal of which the waveform substantially corresponds to that of the AC voltage in the electrical conductor 102. Therefore, there is no timeout when the detection signal passes to zero. Furthermore, since it is maintained in conduction, the LED 108 presents a low dynamic resistance which is of the order of about a few tens of ohms. As a result, the RC value of the sensor is less than that of a sensor in which the LED would not be operated in conduction and the bandwidth is also increased with respect to a sensor in which the LED is not operated in conduction. For example, the bandwidth may be increased by a factor of ten or more, e.g. 200 kHz compared to 10kHz when the LED is not operated in conduction.

[0068] In one embodiment, the operation of the LED in conduction allows requiring an AC current having a lower intensity in order to generate light in comparison to a sensor in which the LED is not operated in conduction, since the AC current does not need to reach any threshold current value to generate light. As a result, the dimensions of the optical sensor for detecting the light incoming from the optical waveguide can be reduced while maintaining the quality of the detection signal. [0069] In the following, there is presented two exemplary sensors 104; a first sensor in which the LED is connectable to the electrical conductor 102 and a second contactless sensor in which the LED is not connectable to the electrical conductor 102.

[0070] Figure 2 illustrates one embodiment of a voltage sensor assembly 150 which comprises an LED 152 electrically connectable to a powered electrical conductor 102, such as an electrical wire or cable, in which an AC electric current flows. The voltage sensor assembly 150 comprises the LED 152, an electrically conducting device or floating conductor 154, a source of DC current 156 and an optical waveguide 158. The optical waveguide 158 is positioned so as to collect at least some of the light emitted by the LED 152 and propagate the collected light up to a read-out unit 114. The read-out unit 114 is adapted to detect light and measure the intensity, amplitude and/or power of the detected light. The read-out unit 114 may be further adapted to determine the voltage of the electrical wire 102 using the measured optical intensity, amplitude and/or power of the detected light.

[0071] The electrically-conducting device 154 is electrically connected to a first terminal of the LED 152 via a first electrical connection 160. The second electrical terminal of the LED 152 is electrically connectable to the electrical conductor 102 via a second electrical connection 162. The LED 152 is adapted to emit light, i.e. a light or optical signal, having at least one given wavelength. The electrically-conducting device 154 is positioned adjacent to the electrical conductor 102 and is made of an electrical conductor material. The conducting device 154 may have any adequate shape as long as it extends along an adequate length of the electrical conductor 102. For example, the electrically- conducting device 154 may be a substantially planar body extending along an axis parallel to the longitudinal axis of the electrical wire 102 and made of an electrically-conducting material such as a metal. In another example, the electrically-conducting device 154 may surround a portion of the cross-sectional perimeter of the electrical conductor 102 or entirely surround the electrical conductor 102. In such a configuration in which the electrically-conducting device 154 entirely surrounds the perimeter of the electrical conductor 102, the electrically-conducting device 154 forms a Faraday cage. [0072] In one embodiment, the electrical connection 162 is removably connectable to the electrical conductor 102 so that the voltage sensor assembly 150 be disconnectable from the electrical conductor 102. In another embodiment, the electrical connection 162 is permanently connected to the electrical conductor 102 so that the voltage sensor assembly 150 be permanently connected to the electrical conductor 102.

[0073] It should be understood that the voltage sensing system 150 may further comprise a sensor casing or body (not shown) in which the LED 152, the electrically- conducting device 154, the DC current source 156 and the electrical connections 160 and 162 are contained. The casing may be adapted to be removably or permanently secured to the electrical conductor 102. In one embodiment, the electrically-conducting device 154 may be integral with the casing so as to form a part thereof. It should also be understood that the casing comprises an aperture to allow the insertion of the optical waveguide 158 therein so as to optically connect one end of the optical waveguide 158 to the LED 152. In one embodiment, the optical waveguide 158 may be secured to the casing.

[0074] In order to measure a light signal representative of the AC voltage in the electrical conductor 102, a DC current is applied by the DC current source to the LED 152 and the electrical connection 162 is electrically connected to the electrical conductor 102. Upon electrical connection between the LED 152 and the electrical conductor 102, at least some of the electrical surface charges present at the outer surface of the electrical wire 102 are extracted from the outer surface and move towards the electrically-conducting device 154 while passing through the LED 152. The movement of the surface charges thereby generates an AC electrical current that powers the LED 152. Once powered, the LED 152 emits light comprising a DC component caused by the DC current and an AC component caused by the AC current. The AC component of the emitted light is indicative of the number of surface charges that move from the outer surface of the electrical conductor 102 to the electrically-conducting device 154, and therefore of the voltage of the electrical conductor 102. At least part of the light emitted by the LED 152 is coupled in the optical waveguide 158. The light coupled into the optical waveguide 158 propagates along the optical waveguide 158 and is detected by the read-out unit 114. The read-out unit 114 then measures the optical power, amplitude, and/or intensity of the detected light and determines the voltage in the electrical conductor 102 using the measured optical power, amplitude, and/or intensity for the detected light. It should be understood that the voltage of the electrical conductor 102 may be determined from the measured optical power, amplitude, and/or intensity of the light detected by the read-out unit 114 since the amount of light emitted by LED 152, and therefore the amount of light coupled into the optical waveguide 158 depends on the AC electrical current that flows through the LED 152 which in turn depends on the derivative of the voltage in the electrical conductor 102.

[0075] In an embodiment in which the electrically-conducting device 154 does not surround the electrical conductor 102, only some of the surface charges move towards the electrically-conducting device 154. In an embodiment in which the electrically-conducting device 154 surrounds a given portion of the electrical conductor 102, substantially all of the surface charges present at the surface of the given portion of the electrical conductor 102 move towards the electrically-conducting device 154. In this case, the electrically- conducting device 154 corresponds to a Faraday cage as described above.

[0076] In one embodiment, the LED 152 is chosen so that the voltage required to power the LED 152 is less than the voltage in the electrical conductor 102. In one embodiment, the voltage required for powering the LED 152 is low enough so that the LED 152 acts as a quasi short-circuit between the electrical conductor 102 and the electrically-conducting device 154.

[0077] In one embodiment, the LED 152 is a micro-LED that is adapted to efficiently convert weak electrical currents into light signals. In one embodiment, a micro- LED is a light source that operates at a voltage that is equal to or less than about 1 % of the voltage to be sensed in the electrical conductor 102.

[0078] In one embodiment, the voltage sensor system 150 may further be adapted to measure the phase of the voltage in the electrical conductor 102 when the LED 152 has a sufficiently fast response time to allow the read-out unit 114 to temporally resolve the signal with a few harmonics. For example, at least some LED sources can meet this condition. Since the variation of voltage between the electrical conductor 102 and the electrically-conducting device 154 creates the AC electrical current that powers the LED 152 and if any parasitic resistance and inductance are neglected, the AC electrical current flowing through the LED 152 is proportional to the derivative of the voltage. The amplitude of the light generated by LED 152 may then be determined using the current applied to the LED 152 and the transfer function of the LED 152. Therefore, the voltage may be determined using the amplitude of the optical signal generated by the LED 152 and the reverse transfer function of the LED 152. It should be understood that the phase and the harmonics of the voltage may also be determined using the same method.

[0079] In one embodiment, the optical waveguide 158 is chosen so as to be sufficiently long for electrically isolating the read-out unit 114 from the electrical conductor 102.

[0080] In one embodiment, the optical waveguide 158 is made of a non-conducting material such as glass or polymer and the read-out unit 114 is electrically insulated from the voltage sensing assembly 150. In one embodiment, the optical waveguide 158 is an optical fiber which may be made of glass (silica), plastic, or polymer. The optical fiber may also be sheathed with a highly effective insulating material. The material used can have a breakdown voltage greater than that of the air. This high degree of electrical isolation and breakdown resistance could be an even greater advantage at medium or even high voltages.

[0081] In one embodiment, the optical waveguide 158 extending between the

LED 152 and the read-out unit 114 is an optical fiber or any light guide which does not require power for operation and does not need to carry electricity. It simply carries an optical signal from the LED 152 to the read-out unit 114. The optical signal is strong enough to ensure readability of the optical signal at a location away from the LED 152, for example at a location meters or tens of meters away from the location of the LED 152, even when using plastic optical fibers. This optical signal is therefore unaffected by electromagnetic perturbations in the environment of the optical fiber. As mentioned above, it can also act as an electrical insulator between the sensing sub-system and the read-out sub-system. [0082] In one embodiment, the use of an optical fiber provides a high degree of electromagnetic interference immunity and excellent electrical isolation and breakdown resistance. The voltage sensor assembly 150 is inherently safe for the power system, because failure of the voltage sensor assembly 150 does not cause a fault or a short circuit to ground.

[0083] The read-out unit 114 is adapted to transform the measured optical amplitude, intensity, or power and, optionally the measured phase if the LED 152 has a sufficiently fast response time, of the received light signal into an electrical detection signal. As mentioned above, the measured optical amplitude, intensity, or power of the light signal is indicative of the AC voltage of the electrical conductor 102. Furthermore, the measured phase of the light signal is indicative of the phase of the AC electrical current flowing into the electrical conductor 102 since the optical signal detected by the read-out unit 114 is function of the derivative of the voltage of the electrical conductor 102. This optical signal generated by the LED 152 can be measured using a photodetector such as a photodiode, which converts the optical signal into an electrical signal. This electrical signal represents the optical amplitude, intensity or power of the light signal over time, and optionally the phase of the light signal over time.

[0084] The read-out unit 114 may comprise a data analysis unit which could include printed circuit boards with data processing capabilities, such as a processor or processing unit to allow analysis of the electrical signal generated by the photodetector. For example, instantaneous voltage and phase readings could be extracted, averages could be calculated, time-stamping and event recordation could be performed, historical data could be cumulated, harmonic content analysis could be performed. The data could be further transmitted to other modules, such as anomaly-detection algorithms to allow an in-depth analysis of the grid. As will be readily understood, the electrical signal could be converted to a digital signal.

[0085] In one embodiment, a calibration step may be required. In an embodiment in which the LED 152 comprises at least one micro-LED, the characterization of the micro- LED temperature behavior and the development of a signal compensation approach may be required as will be understood by one skilled in the art. It may be sufficient to simply calibrate the micro-LED at different temperatures for example. If the behavior of the micro- LED as a function of temperature is reproducible, the calibration approach may be appropriate.

[0086] Calibration tests can be carried out to determine the impact of parameters such as temperature, presence of other electrical fields in the area, electromagnetic noise, magnetic fields, etc., on the reading obtained by the voltage sensing system 20. A calibration adjustment can then be done on the measured voltage to increase accuracy of the reading.

[0087] It should be understood that any adequate source of DC current adapted to deliver an adequate DC current to power the LED 152 may be used. In one embodiment, the source of DC current is adapted to deliver a DC current of which the intensity is substantially equal to or greater than the peak intensity of the AC current flowing through the LED 152.

[0088] In one embodiment, the DC current source 156 comprises a current supply connected to the LED 152 and a battery for powering the current supply.

[0089] In one embodiment, the battery is rechargeable.

[0090] In one embodiment, the voltage sensor assembly 150 comprises additional components to recharge the rechargeable battery using either the charges of the electrical conductor 102 or the electromagnetic field generated by the electrical conductor 102.

[0091] Figure 3 illustrates one embodiment of a voltage sensor assembly 200 for sensing the AC voltage of a powered electrical conductor 102, which comprises a source of DC current that takes advantage of the electromagnetic field generated by the electrical conductor 102 to generate a DC current.

[0092] Regarding the electrical conductor 102 in which an AC current flows and considering the positive portion of the AC cycle, the internal electrical charge in the electrical conductor 102 is equal to zero and the electrical field within the electrical conductor 102 is close to zero. Only a slight longitudinal electrical field is present to allow motion of the electrical charges to create the AC current flowing within the electrical conductor 102. Usually this longitudinal electrical field is weak since electrical conductors are designed to minimize the losses of electrical potential for the AC currents at which they operate. As a result, positive electrical charges accumulate at the outer surface of the electrical conductor 102. These surface charges define the potential, i.e. the voltage, of the electrical wire within a given environment.

[0093] The voltage sensor assembly 200 comprises a LED 202, a casing 204 securable to the electrical conductor 102 and an optical fiber 208 for propagating light emitted by the LED 202 up to a read-out unit 114. The LED 202 is enclosed within the casing 204. At least a portion of the optical fiber 208 extends within the casing 204 so that a first end of the optical fiber 208 be optically coupled to the LED 202 while the remaining of the optical fiber 208 extends outside of the casing 204 so that the other end of the optical fiber 208 be optically coupled to the read-out unit 114.

[0094] The voltage sensor assembly 200 further comprises an electromagnetic induction power generator 210, a rechargeable battery 212, a rectifier (not shown) and a current supply 214, which are all enclosed within the casing 204. The electromagnetic induction power generator 210, the rechargeable battery 212, the rectifier and the current supply 214 form together a DC current source. The electromagnetic induction power generator 210 is adapted to convert an electromagnetic field into an electromotive force. When the casing 204 is secured to the electrical conductor 102, the electromagnetic induction power generator 210 is positioned adjacent to the electrical conductor 102 within the electromagnetic field generated by the electrical conductor 102. As a result, the electromagnetic induction power generator 210 converts part of the electromagnetic field generated by the electrical conductor 102 into an electromotive force which is used for recharging the rechargeable battery 212. The rechargeable battery is used for powering the current supply 214 which is connected in parallel to the LED 202.

[0095] In one embodiment, the battery 212 may be omitted and the electromagnetic induction power generator 210 may be used for directly powering the current supply 214. [0096] As illustrated in Figure 3, the casing 204 comprises a hollow cylindrical body 216 made of an electrically-conducting material and two circular bodies 218 and 220 each made of an electrical insulating or dielectric material. The body 216 corresponds to the electrically-conducting device 110, 154 to be used for generating the AC electrical current in order to power the LED 202. The hollow cylindrical body 216 defines a cavity and the diameter of the cylindrical body 216 is chosen so that the cavity may accommodate at least the DC current source 206, the LED 202 and the electrical connectors for electrically connecting the LED 202 to the electrical conductor 102 and to the hollow cylindrical body 216. The cylindrical body 216 extends between a first end and a second end along a longitudinal axis which corresponds to the longitudinal axis of the electrical conductor 102. The circular body 218 is secured at the first end of the cylindrical body 216 while the circular body 220 is secured at the other end of the cylindrical body 216. The circular bodies 218 and 220 are positioned substantially perpendicularly to the longitudinal axis of the cylindrical body 216 and their outer diameter substantially corresponds to the inner diameter of the cylindrical body 216 so that they snuggingly fit into the cavity of the cylindrical body 216. The circular bodies 218 and 220 each further comprise a central circular aperture for receiving the electrical conductor 102. The diameter of the aperture is substantially equal to the outer diameter of the electrical conductor 102. The circular body 220 further comprises a fiber receiving aperture through which the optical fiber 208 extends.

[0097] The LED 202 is secured within the cavity of the cylindrical conducting body 216 and a first electrical terminal of the LED 202 is electrically connected to the internal surface of the cylindrical conducting body 216. The second electrical terminal of the LED 202 is connectable to the electrical conductor 102.

[0098] When the voltage sensor assembly 200 is positioned on the electrical conductor 102, the second terminal of the LED 202 is electrically connected to the electrical conductor 102. Surface charges may then move from the surface of the electrical conductor 102 up to the cylindrical body 216 which becomes positively charged during the positive phase of the AC current flowing in the electrical conductor 102. The movement of the surface charges creates an AC electrical current which adds to the DC current coming from the DC current source 206 to powers the LED 202, and the LED 202 emits a light signal which is at least partially optically coupled into the optical fiber 208. The light signal travels within the optical fiber 208 up to the read-out module which detects the light signal and measures its amplitude.

[0099] Figure 4 illustrates one embodiment of a voltage sensor assembly 250 which is adapted to be removably secured to an electrical conductor 102. The voltage sensor assembly 250 comprises a casing formed of two hemi-cylindrical hollow casing bodies 252 and 254 which are pivotally connected together via a hinge connection 256. The body 254 is provided with a hook 258 that cooperates with a protrusion 260 for securing together the bodies 252 and 254. The casing bodies 252 and 254 are made of a non-conducting material such as plastic. Alternatively, the casing bodies 252 and 254 may be made of a conducting material such as metal.

[00100] The internal face of each casing body 252 and 254 is provided with a layer of conducting material 262 and 264, respectively, which each forms a hollow conducting hemi-cylinder. In an embodiment in which the casing bodies 252 and 254 may be made of a conducting material, the layers of conducting material 262 and 264 may be omitted.

[00101] The voltage sensing system 100 further comprises two conducting hemi- cylindrical bodies 266 and 268 which are each optionally concentric with a respective casing body 252, 254. The internal diameter of the hemi-cylindrical bodies 266 and 268 substantially corresponds to the diameter of the electrical conductor 102. Two nonconducting plates 270 and 272 connect the conductor hemi-cylindrical body 266 to the casing body 252 so that the bodies 252 and 266 and the plates 270 and 272 be fixedly secured together while the conducting body 266 and the conducting layer 262 are electrically isolated from one another. Two non-conducting plates 274 and 276 connect the conductor hemi-cylindrical body 268 to the casing body 254 so that the bodies 254 and 268 and the plates 274 and 276 be fixedly secured together while the conducting body 268 and the conducting layer 264 are electrically isolated form one another. [00102] The voltage sensing system 100 also comprises an LED 280 and a DC current source 282 such as the DC current source 206. The DC current source 282 is electrically connected to the LED 280 so as to deliver a DC current to the Led 280. The LED 280 is electrically connected to the conducting hemi-cylindrical body 262 and to the conducting hemi-cylindrical body 266.

[00103] In order to measure the AC voltage of the electrical conductor 102, the voltage sensor assembly 250 is removably secured to the electrical conductor 102 by inserting the electrical conductor 102 between the two hemi-cylindrical bodies 266 and 268, abutting the plates 270 and 272 against the plates 274 and 276, respectively, and securing the hook 258 to the protrusion 260. When in the closed position, i.e. when the two hemi-cylindrical casing bodies 252 and 254 are secured together, the voltage sensor assembly 250 is removably secured to the electrical conductor 102. In this case, the hemi- cylindrical bodies 266 and 268 are in physical contact with the electrical conductor 102. When the hemi-cylindrical bodies 266 and 268 are in electrical contact with the electrical conductor 102, surface charges present at the surface of the electrical conductor 102 flow from the electrical conductor 102 to the conducting hemi-cylinders 262 and 264, thereby generating an AC current which adds to the DC current delivered by the DC current source 282 to power the LED 280. The LED 280 then emits light which is at least partially coupled into an optical fiber 286.

[00104] In one embodiment, insulating caps such as the circular bodies 218 and 220 shown in Figure 3 are present at each end of the voltage sensor assembly 250.

[00105] In one embodiment, the length of the voltage sensor assembly 250 along its longitudinal axis is comprised between about 20 cm and about 50 cm.

[00106] The voltage sensor assembly 250 gives a direct measurement of the surface charge of the electrical conductor 102. It does not provide a measurement of the voltage in the electrical conductor 102. However, knowing the electrical conditions of the installation of the conductor 102 and sensor or via calibration, the voltage in the electrical conductor 102 can be extrapolated from the measured surface charge of the electrical conductor 102, as described above.

[00107] Since the voltage sensor assembly 250 forms a Faraday cage and therefore the electromagnetic field within the Faraday cage is null, the measurements made by the voltage sensor assembly 250 are not sensitive to the relative permittivity of the material comprised between the electrical sensor assembly 250 and the conducting hemi-cylindrical bodies 262 and 264, i.e. the electrically-conducting device. In one embodiment, this insensitivity to the relative permittivity offers a large choice for the material for the sensor.

[00108] While Figure 4 show a hook 258 and a protrusion 260 for removably securing together the casing bodies 252 and 254, it should be understood that any adequate securing means may be used such as a clamp system, a screw, etc.

[00109] It should also be understood that the packaging and configuration of the components forming the voltage sensor assembly 250 may vary and be optimized by one skilled in the art. For example, any adequate casing which allows securing, removably or not, the sensor assembly 250 to an electrical conductor of which the voltage is to be sensed, may be used.

[00110] While Figures 3 and 4 illustrate a voltage sensor assembly 200, 250 which comprises an electromagnetic induction power generator 210 for generating electricity and recharging a rechargeable battery 212, Figure 5 illustrates one embodiment of a voltage sensor assembly 300 which comprises a transformer 302 for generating electricity.

[00111] The voltage sensor assembly 300 comprises the transformer 302, a rechargeable battery 304, a rectifier (not shown), a DC current supply 306, an LED 308, and an optical fiber 310. The transformer 302, the rechargeable battery 304, the rectifier and the DC current supply 306 form together a DC current source. The voltage sensor assembly 300 further comprises a casing in which all components are enclosed. The casing comprises a first casing portion 312 and a second casing portion 314. The first casing portion 312 includes a first hollow and conducting cylindrical body 316 made of an electrically conducting material and the second casing portion 314 includes a second hollow and conducting cylindrical body 318 also made of an electrically conducting material. The first and second cylindrical bodies 316 and 318 are each adapted to be secured around the electrical conductor 102. When secured to the electrical conductor 102, the first and second cylindrical bodies 316 and 318 are electrically isolated from one another. For example, the first and second cylindrical bodies 316 and 318 may be spaced apart from one another. In another example, the first and second cylindrical bodies 316 and 318 may be secured together via an electrically isolating device.

[00112] In the illustrated embodiment, the rechargeable battery 304, the DC current supply 306 and the LED 308 are located within the first cylindrical body 316 while the transformer 302 is located within the second cylindrical body 318. The LED 308 has a first terminal electrically connected to the cylindrical body 316 and a second terminal connectable to the electrical conductor 102. The transformer 302 has a first terminal electrically connected to the second cylindrical body 318 and a second terminal electrically connectable to the electrical conductor 102. When the first cylindrical body 316 is secured to the electrical conductor 102, the LED 308 is connected to the electrical conductor 102. Similarly, when the second cylindrical body 318 is connected to the electrical conductor 102, the transformer 302 is electrically connected to the electrical conductor 102.

[00113] When the transformer 302 is electrically connected to the electrical conductor 102, surface charges present at the surface of the electrical conductor 102 moves towards the cylindrical body 318 and the transformer 302 transforms the movement of surface charges into an electrical current that is used to recharge the battery 304.

[00114] When the LED 308 is electrically connected to the electrical conductor 102, surface charges present at the surface of the electrical conductor 102 moves towards the cylindrical body 316. The movement of the surface charges between the electrical conductor 102 and the cylindrical body 316 creates an AC current that powers that the LED 308 in addition to the DC current supplied by the DC current source.

[00115] It should be understood that the battery 304 may be omitted. In this case, the transformer 302 is used for powering the LED 308. [00116] As described above, the light emitted by the LED is indicative of both the

DC current coming from the current source and the AC current resulting from the movement of surface charges between the electrical conductor 102 and the cylindrical body 316. The light emitted by the LED 308 is at least partially coupled into the optical fiber 310 which propagates the coupled light up to the read-out unit 114.

[00117] In one embodiment, the casing further comprises two circular bodies 320 and 322 each made of an electrical insulating or dielectric material. The circular body 320 is secured at the end of the cylindrical body 316 that is opposite to the cylindrical body 318. The circular body 322 is secured at the end of the cylindrical body 318 that is opposite to the cylindrical body 316. The circular bodies 320 and 322 are positioned substantially perpendicularly to the longitudinal axis of their respective cylindrical body 316, 318 and their outer diameter substantially corresponds to the inner diameter of their respective cylindrical body 316, 318 so that they snuggingly fit into the cavity of their respective cylindrical body 316, 318. The circular bodies 320 and 322 each further comprise a central circular aperture for receiving the electrical conductor 102. The diameter of the aperture is substantially equal to the outer diameter of the electrical conductor 102. The circular body 320 further comprises a fiber receiving aperture through which the optical fiber 310 extends.

[00118] In one embodiment, the voltage sensor assembly 200, 250, 300 further comprises a rectifier (not shown) for converting AC current into DC current. For example, if the electromagnetic induction power generator 210 is adapted to output an AC current, a rectifier may be positioned between the electromagnetic induction power generator 210 and the light source or the battery 212, if any, so that an adequate DC current may be used for powering the light source or charging the rechargeable battery 212, if any. If the transformer 302 outputs an AC current, a rectifier may be positioned between the transformer 302 and the battery 304 so that an adequate DC current may be used for charging the rechargeable battery 304.

[00119] In one embodiment, the battery 304 may be omitted and the transformer 302 may be used to power the current supply 306. [00120] In one embodiment, the above-described voltage sensor assembly 150 may be used for measuring voltages in the conductor cables or wires of a power transmission line. Figure 6 illustrates one embodiment of a voltage sensing system 330 to be installed on a three-phase power or overhead transmission line comprising three bundle conductors 332, 334, and 336 positioned in parallel along a given axis. The bundle conductor 332 is positioned between the bundle conductors 332 and 336. The three conductors 332, 334, and 336 each carry an AC current of the same frequency and voltage amplitude relative to a common reference but with a phase difference of one third of the period. Therefore, the first bundle conductor 332 is associated with a first phase, i.e. phase 1, the second bundle conductor 334 is associated with a second phase, i.e. phase 2, while the third bundle conductor is associated with a third phase, i.e. phase 3. Each bundle conductor 332, 334, 336 is provided with a respective voltage sensing system or voltage sensor 338, 340, 342, respectively, that is removably or permanently secured to its respective bundle conductor 332, 334, 336.

[00121] The voltage sensor 338 comprises four elongated and curved plates 344a-

344d which each extend along the same longitudinal axis as the longitudinal axis of the bundle conductor 332 when the voltage sensor 338 is connected to the bundle conductor 332. Each plate 344a-344d is made of an electrically-conducting material so that the four plates 344a-344d form together the above-described electrically-conducting device. The cross-section of each plate 344a-344d in a plane orthogonal to the longitudinal axis presents a curved or semi-circular shape. The voltage sensor 338 also comprises a sensing sub-assembly 345 including a micro-light source optically coupled to an optical fiber (not shown) for propagating the light emitted by the micro-light source 345 up to a read-out module (not shown) and a current source for powering the micro-light source as described above. The micro-light source of the sensing sub-assembly 345 is electrically connected to the conducting plate 344a and electrically connectable to the bundle conductor 332. Each conducting plate 344b-344d is individually and directly connectable to the bundle conductor 332 via any adequate electrical connector. [00122] In one embodiment, the sensing sub-assembly 345 comprises a battery for powering a current supply. In an embodiment in which the battery is rechargeable, the sensing sub-assembly 345 may further comprise an electromagnetic induction power generator as described above. Alternatively, the sensing sub-assembly 345 may further comprise a transformer for charging the rechargeable battery, as described above.

[00123] In one embodiment, the conducting plates 344a-344d are secured together using two sets of two insulating hemi-circular plates, each set being positioned at a respective end of the voltage sensor 338. The connection system may be used for the voltage sensors 340 and 342.

[00124] The voltage sensor 340 comprises four elongated and curved plates 346a-

346d which each extend along the same longitudinal axis as the longitudinal axis of the bundle conductor 334 when the voltage sensor 340 is connected to the bundle conductor 334. Each plate 346a-346d is made of an electrically-conducting material so that the four plates 346a-346d form together the above-described electrically-conducting device. The cross-section of each plate 346a-346d in a plane orthogonal to the longitudinal axis presents a curved or semi-circular shape. The voltage sensor 340 also comprises a first sensing sub-assembly 348 which includes a first micro-light source optically coupled to an optical fiber (not shown) for propagating the light emitted by the micro-light source up to a read-out module (not shown) and a first current source for powering the first micro-light source. The first micro-light source is electrically connected to the conducting plate 346c and electrically connectable to the bundle conductor 334. The voltage sensor 340 further comprises a second sensing sub-assembly 350 which includes a second micro-light source optically coupled to an optical fiber (not shown) for propagating the light emitted by the micro-light source up to the read-out module and a second current source for powering the second micro-light source. The micro-light source is electrically connected to the conducting plate 346a and electrically connectable to the bundle conductor 334. Each conducting plate 346b and 346d is individually and directly connectable to the bundle conductor 334 via any adequate electrical connector. It should be understood that the voltage sensor 340 may comprise a single current source used for powering both the first and second micro-light sources. In this case, the single current source may comprise two independent outputs each connected to a respective micro-light source.

[00125] In one embodiment, the current source(s) comprise(s) at least one current supply and at least one battery for powering the current supply(ies). In an embodiment in which the at least one battery is rechargeable, the sensing sub-assembly 350 may further comprise at least one electromagnetic induction power generator as described above. Alternatively, the sensing sub-assembly 350 may further comprise a transformer for charging the rechargeable battery(ies), as described above.

[00126] In one embodiment, the purpose of the conducting plates 344b, 344c, and

344d, which are directly connectable to the bundle conductor 332 without any light source, is to complete the surrounding wall having curved edges for enclosing the bundle conductor 332. The curved edges decrease the risk of external electrical discharge. In the same or another embodiment, the purpose of the conducting plates 344a, 344b, 344c, and 344d is to maintain an adequate measurement precision in case of bad weather such as rain, ice, snow, and/or the like. In this case, the top portion of the resulting surrounding wall protects the voltage sensor from adverse weather conditions.

[00127] The voltage sensor 342 comprises four elongated and curved plates 352a-

352d which each extend along the same longitudinal axis as the longitudinal axis of the bundle conductor 336 when the voltage sensor 342 is connected to the bundle conductor 336. Each plate 352a-352d is made of an electrically-conducting material so that the four plates 352a-352d form together the above-described electrically-conducting device. The cross-section of each plate 352a-352d in a plane orthogonal to the longitudinal axis presents a curved or semi-circular shape. The voltage sensor 342 also comprises a sensing sub-assembly 354 which includes a micro-light source optically coupled to an optical fiber (not shown) for propagating the light emitted by the micro-light source up to the read-out module, and a current source for powering the micro-light source. The micro-light source is electrically connected to the conducting plate 352c and electrically connectable to the bundle conductor 336. Each conducting plate 352a, 352b, and 352d is individually and directly connectable to the bundle conductor 336 via any adequate electrical connector. [00128] In one embodiment, the sensing sub-assembly 354 comprises a current supply and a battery for powering the current supply. In an embodiment in which the battery is rechargeable, the sensing sub-assembly 354 may further comprise an electromagnetic induction power generator as described above. Alternatively, the sensing sub-assembly 354 may further comprise a transformer for charging the rechargeable battery, as described above.

[00129] While the voltage sensors 338, 340 and 342 each comprise four electrically- conducting plates 344a-344d, 346a-346d, and 352a-352d, respectively, it should be understood that the number of electrically-conducting plates may vary. For example, each voltage sensor 338, 340, 342 may comprise a single tubular electrically-conducting plate that surrounds a respective bundle conductor 332, 334, 336. In another example, each voltage sensor 338, 340 and 342 may comprise two hemi-tubular electrically-conducting plates which, when connected together, surround a respective bundle conductor 332, 334, 336. It should also be understood that the shape of the electrically-conducting plate(s) may vary. For example, the electrically-conducting plates may be flat or planar, curved, hemi- tubular, or the like.

[00130] By dividing the electrically-conducting device into several conducting parts, e.g. into four conducting plates 344a-344d as in the illustrated embodiment, it is possible to choose to which electric field the sensor will be the most sensitive. Each conducting piece or conducting plate 344a-344d is more sensitive to electrical sources located substantially perpendicular to its surface and less sensitive to electrical sources positioned on a side thereof. The same applies to the conducting plates 346a-346d and 352a-352d.

[00131] Therefore, the conducting plate 346c is mainly sensitive to the phase 1 conductor, i.e. the bundle conductor 332, and the light source of the sensing subassembly 348 which is connected to the conducting plate 346c will provide information about the difference of electric potential between the bundle conductors 332 and 334, i.e. between phases 1 and 2. The conducting plate 346a is mainly sensitive to the phase 3 conductor, i.e. the bundle conductor 336, and the light source of the sensing subassembly 350 which is connected to the conducting plate 346a will provide information about the difference of electric potential between the bundle conductors 334 and 336, i.e. between phases 2 and 3. The conducting plate 344a of the voltage sensor 338 is mainly sensitive to the phase 2 conductor, i.e. the bundle conductor 334 but is also sensitive to the phase 3 conductor, i.e. the bundle conductor 336. The conducting plate 352c of the voltage sensor 342 is mainly sensitive to the phase 2 conductor, i.e. the bundle conductor 334 but also sensitive to the phase 1 conductor, i.e. the bundle conductor 332. In this case, the readout module is adapted to determine the voltage of the three bundle conductors 332, 334, 336 using the measured light amplitudes, intensities or powers coming from the four micro- light sources.

[00132] Figure 7 illustrates another embodiment of a voltage sensing system 358 for measuring the voltage in three bundle conductors 359, 360, and 361. In this embodiment, the voltage sensing system 178 comprises three voltage sensors 362, 364, and 366 each connectable to a respective bundle conductor 359, 360, and 361. Each voltage sensor 362, 364, 366 comprises a casing in which at least one micro-light source is enclosed and an optical waveguide for collecting the light emitted by the micro-light source. Each casing comprises four elongated plates which are disposed so as to enclose a respective bundle conductor 359, 360, 361.

[00133] The voltage sensor 362 comprises a casing formed of a curved top plate 368a, two side plates 368b and 368c, and a bottom plate 368d. The voltage sensor 362 further comprises a sensing sub-assembly 370 which includes a micro-light source and a current source for powering the micro-light source. The side plate 368b is made of a conducting material and is electrically connected to the micro-light source of the sensing sub-assembly 370 which is electrically connectable to the bundle conductor 359. The plates 368a, 368c, and 368d are each made of a conducting material and each connectable to the bundle conductor 359. The plates 368a-368d are shaped and sized so that the casing protects at least the microlight source from precipitation such as rain, snow, and/or the like. The curved plate 368a is provided with rounded ends which are each adjacent to a respective side plate 368b, 368c. The rounded ends are each inwardly curved so that any precipitation received by the top plate 368a flows away from the side plates 368b and 368c and no electrical contact be created between the top plate 368a and the side plates 368b and 368c. The bottom plate 368d is also provided with rounded or curved ends to protect the interior of the casing.

[00134] The side plate 368b which is electrically connected to the micro-light source of the sensing sub-assembly 370 is oriented so as to be substantially orthogonal to the axis that passes by the bundle conductors 360 and 361 in order to be sensitive to these two bundle conductors. The plates 368a-368d are connected together using a non-conducting or electrically insulating material to ensure that the light signal emitted by the micro-light source comes only from the movement of surface charges between the bundle conductor 359 and the plate 368b. Furthermore, electrically connecting all of the plates 368a-368d to the bundle conductor 359 ensures that substantially no electric discharge will occur between the plates 368a-368d.

[00135] In one embodiment, the sensing sub-assembly 362 comprises a current supply and a battery for powering the current supply. In an embodiment in which the battery is rechargeable, the sensing sub-assembly 362 may further comprise an electromagnetic induction power generator as described above. Alternatively, the sensing sub-assembly 362 may further comprise a transformer for charging the rechargeable battery, as described above.

[00136] The voltage sensor 364 comprises a casing formed of a curved top plate 372a, two side plates 372b and 372c, and a bottom plate 372d. The voltage sensor 364 further comprises a first sensing sub-assembly 374 and a second sensing sub-assembly 376. The first sensing sub-assembly 374 includes a first micro-light source and a first current source for powering the first micro-light source. The second sensing sub-assembly 376 includes a second micro-light source and a second current source for powering the second micro-light source. The side plate 372b is made of a conducting material and is electrically connected to the micro-light source of the first sensing sub-assembly 374, which is electrically connectable to the bundle conductor 360. The side plate 372c is made of a conducting material and is electrically connected to the micro-light source of the second sensing sub-assembly 376, which is electrically connectable to the bundle conductor 360. The plates 372a and 372d are each made of a conducting material and each connectable to the bundle conductor 360. The plates 372a-372d are shaped and sized so that the casing protects at least the microlight source from precipitation such as rain, snow, and/or the like. The curved plate 372a is provided with rounded ends which are each adjacent to a respective side plate 372b, 372c. The rounded ends are each inwardly curved so that any precipitation received by the top plate 372a flows away from the side plates 372b and 372c and no electrical contact be created between the top plate 372a and the side plates 372b and 372c. The bottom plate 372d is also provided with rounded or curved ends to protect the interior of the casing.

[00137] It should be understood that the voltage sensor 364 may comprise a single current source for powering both the micro-light source of the first sensing subassembly 374 and the micro-light source of the second sensing sub-assembly 376. The single current source comprises two independent outputs which are each connected to a respective micro-light source.

[00138] The side plate 372b which is electrically connected to the micro-light source of the first sensing sub-assembly 374 is oriented so as to be substantially orthogonal to the bundle conductor 361 in order to be sensitive to this bundle conductor. The side plate 372c which is electrically connected to the micro-light source of the second sensing subassembly 376 is oriented so as to be substantially orthogonal to the bundle conductor 359 in order to be sensitive to this bundle conductor. The plates 372a-372d are connected together using a non-conducting or electrically insulating material to ensure that the light signal emitted by the micro-light source of the first sensing sub-assembly 374 comes only from the movement of surface charges between the bundle conductor 360 and the plate 372b and the light signal emitted by the micro-light source of the second sensing sub-assembly 376 comes only from the movement of surface charges between the bundle conductor 360 and the plate 372c. Furthermore, electrically connecting all of the plates 372a-372d to the bundle conductor 360 ensures that substantially no electric discharge will occur between the plates 372a-372d. [00139] In one embodiment, the sensing sub-assembly 364 comprises at least one current supply and at least one battery for powering the current supply(ies). In an embodiment in which the at least one battery is rechargeable, the sensing sub-assembly 364 may further comprise at least one electromagnetic induction power generator as described above. Alternatively, the sensing sub-assembly 364 may further comprise a transformer for charging the rechargeable battery(ies), as described above.

[00140] The voltage sensor 366 comprises a casing formed of a curved top plate 378a, two side plates 378b and 378c, and a bottom plate 378d. The voltage sensor 366 further comprises a sensing sub-assembly 379 which includes a micro-light source and a current source for powering the micro-light source. The side plate 378c is made of a conducting material and is electrically connected to the micro-light source of the sensing sub-assembly 379 which is electrically connectable to the bundle conductor 361. The plates 378a, 378b, and 378d are each made of a conducting material and each connectable to the bundle conductor 361. The plates 378a-378d are shaped and sized so that the casing protects at least the microlight source from precipitation such as rain, snow, and/or the like. The curved plate 378a is provided with rounded ends which are each adjacent to a respective side plate 378b, 378c. The rounded ends are each inwardly curved so that any precipitation received by the top plate 378a flows away from the side plates 378b and 378c and no electrical contact be created between the top plate 378a and the side plates 378b and 378c. The bottom plate 378d is also provided with rounded or curved ends to protect the interior of the casing.

[00141] The side plate 378c which is electrically connected to the micro-light source of the sensing sub-assembly 379 is oriented so as to be substantially orthogonal to the axis that passes by the bundle conductors 359 and 360 in order to be sensitive to these two bundle conductors. The plates 378a-378d are connected together using a non-conducting or electrically insulating material to ensure that the light signal emitted by the micro-light source of the sensing sub-assembly 379 comes only from the movement of surface charges between the bundle conductor 361 and the plate 378c. Furthermore, electrically connecting all of the plates 378a-378d to the bundle conductor 361 ensures that substantially no electric discharge will occur between the plates 378a-378d.

[00142] In one embodiment, the sensing sub-assembly 366 comprises a current supply and a battery for powering the current supply. In an embodiment in which the battery is rechargeable, the sensing sub-assembly 366 may further comprise an electromagnetic induction power generator as described above. Alternatively, the sensing sub-assembly 366 may further comprise a transformer for charging the rechargeable battery, as described above.

[00143] The micro-light sources of the sensing sub-assemblies 370, 374, 376, and 379 are each optically connected to a read-out module via at least one optical fiber. The read-out module is adapted to determine the voltage of the bundle conductors 359, 360, and 361 using the light signals received from the micro-light sources of the sensing subassemblies 370, 374, 376, and 379 using the same method as described above with respect to the read-out module described in connection with Figure 6.

[00144] While the voltage sensing systems 330 and 358 are installed on the bundle conductors of a power line, Figure 8 illustrates one embodiment of a voltage sensing system 380 to be installed on two ground conductors 381 and 382 of a power line in order to determine the voltage in the three bundle conductors 383, 384, 385 of the power line. It should be understood that the ground conductors 381 and 382 correspond to electrical conductors which are connected to the ground. While they are positioned on top of the three bundle conductors 383, 384, and 385, it should be understood that the two ground conductors 381 and 382 may be positioned below the three bundle conductors 383, 384, and 385. The ground conductor 381 is located between the bundle conductors 383 and 384 while the ground conductor 382 is located between the bundle conductors 384 and 385.

[00145] The voltage sensing system 380 comprises two voltage sensors 386 and 387.

Each voltage sensor 386, 387 comprises a casing in which two micro-light sources are enclosed and at least one optical waveguide for collecting and guiding the light emitted by the micro-light sources. Each casing comprises four elongated plates which are disposed so as to enclose a respective ground conductor 381, 382.

[00146] The voltage sensor 386 comprises a casing formed of a curved top plate 388a, two side plates 388b and 388c, and a bottom rounded plate 388d. The voltage sensor 386 further comprises a first sensing sub-assembly 389 and a second sensing subassembly 390. The first sensing sub-assembly 389 includes a first micro-light source and a first current source for powering the first micro-light source. The second sensing subassembly 390 includes a second micro-light source and a second current source for powering the first micro-light source. The side plate 388b is made of a conducting material and is electrically connected to the micro-light source of the first sensing sub-assembly 389, which is electrically connectable to the bundle conductor 381. The side plate 388c is made of a conducting material and is electrically connected to the micro-light source of the second sensing sub-assembly 390, which is electrically connectable to the ground conductor 381. The plates 388a and 388d are each made of a conducting material and each connectable to the ground conductor 381. The plates 388a-388d are shaped and sized so that the casing protects at least the microlight sources of the first and sensing subassemblies 389 and 390 from precipitation such as rain, snow, and/or the like. The curved plate 388a is provided with rounded ends which are each adjacent to a respective side plate 388b, 388c. The rounded ends are each inwardly curved so that any precipitation received by the top plate 388a flows away from the side plates 388b and 388c and no electrical contact be created between the top plate 388a and the side plates 388b and 388c.

[00147] The side plate 388b which is electrically connected to the micro-light source of the first sensing sub-assembly 389 is oriented so as to be more sensitive to the electric fields generated by the bundle conductors 384 and 385. The side plate 388c which is electrically connected to the micro-light source of the second sensing sub-assembly 390 is oriented so as to be more sensitive to the electromagnetic field generated by the bundle conductor 383. The plates 388a-388d are connected together using a non-conducting or electrically insulating material to ensure that the light signal emitted by the micro-light source of the first sensing sub-assembly 389 comes only from the movement of surface charges between the ground conductor 381 and the plate 388b and the light signal emitted by the micro-light source of the second sensing sub-assembly 390 comes only from the movement of surface charges between the ground conductor 381 and the plate 388c. Furthermore, electrically connecting all of the plates 388a-388d to the ground conductor 381 ensures that substantially no electric discharge will occur between the plates 388a-388d. It should be understood that the voltages in the conductors 383, 384 and 385 may be determined from the optical signals emitted from the micro-light sources of the sensing sub-assemblies 389, 390, 392, and 393 since the surface charges present at the surface of the ground conductors 381 and 382 depend on the surface charges present at the surface of the bundle conductors 383, 384, and 385, and the surface charges present at the surface of the bundle conductors 383, 384, and 385 depend on the voltages in the bundle conductors 383, 384, and 385.

[00148] It should be understood that the voltage sensor 386 may comprise a single current source for powering both the first micro-light source of the first sensing subassembly 389 and the second micro-light source of the second sensing sub-assembly 390. The single current source comprises two independent outputs which are each connected to a respective micro-light source.

[00149] In one embodiment, the voltage sensor 386 further comprises at least one current supply and at least one battery for powering the current supply(ies). In one embodiment, the battery may be a rechargeable battery. In this case, the voltage sensor 386 may further comprise, for each sensing sub-assembly 389, 390, an electromagnetic induction power generator as described above. Alternatively, the voltage sensor 386 may further comprise, for each sensing sub-assembly 389, 390, a transformer for charging the rechargeable battery, as described above. In this case, the voltage sensor 386 further comprises a conducting element to which the transformer is electrically connected and the transformer is further connected to the ground conductor 381.

[00150] The voltage sensor 387 comprises a casing formed of a curved top plate 391a, two side plates 391b and 391c, and a bottom rounded plate 391d. The voltage sensor 387 further comprises a first sensing sub-assembly 392 and a second sensing sub- assembly 393. The first sensing sub-assembly 392 includes a first micro-light source and a first current source for powering the first micro-light source. The second sensing subassembly 393 includes a second micro-light source and a second current source for powering the first micro-light source. The side plate 391b is made of a conducting material and is electrically connected to the micro-light source of the first sensing sub-assembly 392, which is electrically connectable to the bundle conductor 382. The side plate 391c is made of a conducting material and is electrically connected to the micro-light source of the first sensing sub-assembly 393, which is electrically connectable to the ground conductor 382. The plates 391a and 39 Id are each made of a conducting material and each connectable to the ground conductor 382. The plates 391a-391d are shaped and sized so that the casing protects at least the microlight sources of the sensing sub-assemblies 392 and 393 from precipitation such as rain, snow, and/or the like. The curved plate 391a is provided with rounded ends which are each adjacent to a respective side plate 391b, 391c. The rounded ends are each inwardly curved so that any precipitation received by the top plate 391a flows away from the side plates 391b and 391c and no electrical contact be created between the top plate 391a and the side plates 391b and 391c.

[00151] The side plate 391b which is electrically connected to the micro-light source of the first sensing sub-assembly 392 is oriented so as to be sensitive to the electric field generated by the bundle conductor 385. The side plate 391c which is electrically connected to the micro-light source of the second sensing sub-assembly 393 is oriented so as to be sensitive to the electric fields generated by the bundle conductors 383 and 384. The plates 391a-391d are connected together using a non-conducting or electrically insulating material to ensure that the light signal emitted by the micro-light source of the first sensing sub-assembly 392 comes only from the movement of surface charges between the ground conductor 382 and the plate 391b and the light signal emitted by the micro-light source of the second sensing sub-assembly 393 comes only from the movement of surface charges between the ground conductor 382 and the plate 391c. Furthermore, electrically connecting all of the plates 391a-391d to the ground conductor 382 ensures that substantially no electric discharge will occur between the plates 391a-391d. [00152] It should be understood that the voltage sensor 387 may comprise a single current source for powering both the first micro-light source of the first sensing subassembly 392 and the second micro-light source of the second sensing sub-assembly 393. The single current source comprises two independent outputs which are each connected to a respective micro-light source.

[00153] In one embodiment, the voltage sensor 387 further comprises at least one current supply and at least one battery for powering the current supply(ies). In one embodiment, the battery may be a rechargeable battery. In this case, the voltage sensor 387 may further comprise, for each sensing sub-assembly 392, 393, an electromagnetic induction power generator as described above. Alternatively, the voltage sensor 387 may further comprise, for each sensing sub-assembly 392, 393, a transformer for charging the rechargeable battery, as described above. In this case, the voltage sensor 387 further comprises a conducting element to which the transformer is electrically connected and the transformer is further connected to the ground conductor 382.

[00154] In one embodiment, the voltage sensing system 380 may be used when the electric fields generated by the bundle conductors 383, 384, and 385 are strong, e.g. for voltages in the range of hundreds of kV.

[00155] In an embodiment in which a power line comprises more than two ground conductors, the voltage sensing system 380 may be preferably installed on the ground conductors that are closest to the bundle conductors.

[00156] While in the above description it is secured to a ground conductor such as the ground conductor 381, it should be understood that the voltage sensing system 380 may be secured to any other adequate conducting and grounded structure having an electrical charge generated by a separate conductor in which an electrical current flows, such as conductor 383. For example, the voltage sensing system 380 could be secured to the transmission tower on which the conductors are mounted. [00157] It should be understood that the voltage sensing system may comprise a single sensing sub-assembly when the voltage of a single powered conductor is to be determined.

[00158] While Figures 2 to 7 illustrate exemplary embodiments of a voltage sensor assembly which comprises an LED electrically connectable to an electrical conductor of which the AC voltage is to be sensed, the following presents contactless voltage sensor assemblies, i.e., voltage sensors assemblies which are not electrically connected to the electrical conductor to sense its voltage.

[00159] Figure 9 schematically illustrates one embodiment of a contactless voltage sensor assembly 400 for sensing the AC voltage of a powered electrical conductor 102. The voltage sensor assembly 400 comprises a DC current source 402, an LED 404, an electrically conducting device 406 and an optical waveguide 408. The optical waveguide 408 has one end that is optically connected to the LED 404 so that at least some of the light emitted by the LED 404 be coupled into the optical waveguide 408. The other end of the optical waveguide 408 is optically coupled to a read-out unit which is adapted to detect the light transmitted over the optical waveguide 404.

[00160] The LED 404 has a first terminal electrically connected to the conducting device 406 and a second terminal electrically connectable to the ground. The conducting device 406 is positioned within in the electromagnetic field generated by the powered electrical conductor 102 so that when the LED 404 is connected to the ground, a movement of charges occurs between the conducting device 406 and the ground. The movement of charges between the conducting device 406 and the ground generates an AC current that powers the LED 404.

[00161] The current source 402 is electrically connected in parallel to the LED 404 so as to deliver a DC current to the LED 404. As a result, the current powering the LED 404 comprises a first component being the DC current delivered by the current source 402 and a second component corresponding to the AC current generated by the movement of charges between the powered conductor 102 and the conducting device 406 when the LED 404 is connected to the ground. As describe above, the light emitted by the LED 404 comprises a first component resulting from the DC current generated by the current source 402 and a second component resulting from the AC current generated by the movement of charges. The read-out unit 410 is adapted to detect the incoming light comprising both the first and second components and extract the second component from the detected light and determine the AC voltage of the powered conductor 102.

[00162] In one embodiment, the ground reference can be obtained from the support wire on which powered conductors are often provided. If this ground reference is not available near the conducting device, the ground reference can be obtained elsewhere. A conductive coating could be provided on the optical waveguide. The thin conductive coating would then be connected to a ground reference. A small conducting wire could be added to the cable of the optical waveguide and also be connected to the ground reference. This small conducting wire would not create a short circuit since it would have a low current carrying capacity. One should however avoid creating stray currents. Design of the casing of the voltage sensor may help in limiting stray currents.

[00163] As described above, the current source 402 may comprise a battery. In one embodiment, the battery may be rechargeable. An electromagnetic induction power generator as described above may be used for charging the rechargeable battery. In another embodiment, a transformer may be used for charging the battery. In this case, the current source 402 further comprises a conducting element to which the transformer is electrically connected and the transformer is further connected to the ground.

[00164] Figure 10 illustrates one embodiment of a voltage sensor assembly 430 which comprises two floating conductors 432 and 434 for sensing the AC voltage of a powered conductor 102. In addition to the two floating conductors 432 and 434, the voltage sensor assembly 430 further comprises a current source 436, an LED 438 and an optical fiber 440. The current source 436 is used for powering the LED 438, i.e. for applying an AC or a DC current to the LED 438. [00165] The first floating conductor 432 is located at a first distance LI from the powered conductor 102 while the second floating conductor 434 is located a second and different distance L2 from the powered conductor 102. In the illustrated embodiment, the first distance LI is shorter than the second distance L2. The distances LI and L2 are chosen so that the first and second floating conductors 432 and 434 are located within the electric field of the powered conductor 102. Since the distances LI and L2 are different and the two floating conductors 432 and 434 are located within the electric filed of the powered conductor 102, the first and second floating conductors 432 and 434 are at different electric potentials.

[00166] By electrically connecting the first terminal of the LED 438 to the first floating conductor 432 and the second terminal of the LED 438 to the second floating conductor 434, a movement of charges occurs between the first and second floating conductors 432 and 434. The movement of charges generates an AC current representative of the AC voltage of the powered conductor 102 and the generated AC current is used for powering the LED 438. At least part of the light generated by the LED 438 is collected by the optical fiber 440 and detected by a read-out unit 442.

[00167] As described above, the current source 436 may comprise a battery. In one embodiment, the battery may be rechargeable. An electromagnetic induction power generator as described above may be used for charging the rechargeable battery. In another embodiment, a transformer may be used for charging the battery. In this case, the current source 436 further comprises two floating conducting elements to which the transformer is electrically connected.

[00168] In the following there is presented several examples of contactless voltage sensor assemblies, i.e. sensor voltage assemblies comprising two floating conductors such as the voltage sensor assembly 430, or sensor voltage assemblies comprising a single floating conductor and a ground connection such as voltage sensor assembly 400. In these examples, the powered conductor has an AC voltage causing the charge at the powered conductor to alternate between a -Q and +Q charge. [00169 ] First example embodiment

[00170] In a first Faraday cage example embodiment 450 shown in Figures 11A and

11B, an interior hollow conductive cylinder 452 surrounds an elongated section of the powered conductor 102. An exterior hollow conductive cylinder 454 surrounds the interior conductive cylinder 452. The cylinders 452, 454 are held in relative configuration with each other and with the powered conductor 102 using insulating caps at both ends (not shown). Since the cylinders 452, 454 are longer than their respective diameter, the impact of the insulating caps is negligible. The cylinders 452, 454 are operatively connected by the sensing sub-system including the light source 456 and a DC current source 458. In one example embodiment, the cylinders 452, 454 can have a length of about 20 to about 50 cm. If the powered conductor 102 is unsheathed, the sensor includes an interior insulating layer 460. An intermediate insulating layer such as a layer of air is also provided between the cylinders 452 and 454. The interior insulating layer 460 and the intermediate insulating layer can be filled with air or with a dielectric material such as polymers or ceramics. The cylinders 452 and 454 can be made of any conductive material, such as aluminum, for example.

[00171] It should be understood that when the voltage sensor assembly 450 is secured tot eh powered conductor 102, the conductive cylinders 452 and 454 are located at different distances form the powered conductor 102. As result, the conductive cylinders 452 and 454 are at different electric potentials.

[00172] Considering that exterior electrical fields are negligible and that the conducting device has a null charge at the beginning, when the powered conductor 102 has a +Q charge, the interior cylinder 452 has a -Q charge to cancel out the field. The exterior cylinder 454 has a charge of + Q. When the AC voltage forces the charge at the electrical wire to change from +Q to -Q, a charge of a magnitude 2Q will travel in the sensing subsystem.

[00173] This first example embodiment 450 gives a direct measurement of the charge Q. It varies with the electrical field. It does not provide a measurement of the voltage in the electrical wire. However, knowing the electrical conditions of the installation of the wire and sensor or via calibration, the voltage in the electrical wire can be extrapolated from the charge Q.

[00174] The housing of the sensor 462 has a clamp type configuration to allow clamping of the sensor on the powered conductor 102. In Figure 11 A, the housing is open for installation or removal of the sensor. In Figure 11B, the housing is closed for live measurement of the AC voltage in the powered conductor 102.

[00175] The voltage sensor and the optical fiber 464 are shown schematically at a longitudinal end of the cylinders. As will be readily understood, the packaging and configuration of these components will be optimized by one skilled in the art.

[00176] While in the illustrated embodiment, the current source 458 comprises an electromagnetic induction power generator 466, a rechargeable battery 468 and a current supply 470, it should be understood that any adequate current source adapted to deliver an AC current and/or a DC current to the light source 456 may be used.

[00177] Second example embodiment

[00178] In this third example embodiment 550 shown in Figure 12, the exterior hollow conductive cylinder is omitted. The remaining cylinder 552, a hollow conductive cylinder is grounded via ground link 554.

[00179] When the AC voltage forces the charge to change from +Q to -Q in the powered conductor, a charge of a magnitude 2Q will travel in the ground link. This third example embodiment 550 also gives a direct measurement of the charge Q.

[00180] Third example embodiment

[00181] In this fourth example embodiment 600 shown in Figure 13, a layer of dielectric material 630 is present between the powered conductor and the conductive cylinder 602. The remaining cylinder is still grounded via ground link 620. [00182] The dielectric material gets polarized and a +q charge becomes present near the powered conductor while a -q charge becomes present near the remaining cylinder. If the electrical wire still has a charge of +Q, we know that +Q = +Q'-q and -Q = -Q'+q. The Q' charge measured when a dielectric layer is present will therefore be greater than Q measured when there is no dielectric layer. Indeed, Q7Q=sr, where sr is the relative permittivity of the dielectric material. The charge travelling in the electrical conductor will be 2Q'.

[00183] Fourth example embodiment

[00184] In this fourth example embodiment 700 shown in Figure 14, the conducting device is a single conductive plate 702, optionally provided with an insulation layer 703. It is brought in close proximity to the powered conductor without clamping on it. The shape of the casing 704 helps the user to position the conductive plate 702 in appropriate relative configuration to the powered conductor.

[00185] In one embodiment, the optical waveguide used to propagate the light emitted by the light source up to the read-out unit is an optical fiber or any light guide which does not require power and does not need to carry electricity.. The optical signal emitted by the light source has an intensity value related to the voltage present in the powered conductor. The optical signal is strong enough to ensure readability of the optical signal at a location away from the light source, for example at a location meters or tens of meters away from the location of the voltage sensor, even when using plastic optical fibers. This optical signal is unaffected by electromagnetic perturbations in the environment of the optical fiber. It can also act as an electrical insulator between the voltage sensor and the read-out unit.

[00186] In one embodiment, the read-out unit comprises a detector sub-system adapted to transform the intensity and phase reading of the optical signal into an electrical output signal. This can be done using a detector such as a photodiode. This electrical signal represents the intensity and phase of the light over time. [00187] The detector sub-system is in communications with a data analysis subsystem which could include printed circuit boards with data processing capabilities, such as a processor to allow analysis of the electrical signal. For example, instantaneous voltage and phase readings could be extracted, averages could be calculated, time-stamping and event recordal could be performed, historical data could be cumulated, harmonic content analysis could be performed. The data could be further transmitted to other modules, such as anomaly-detection algorithms to allow an in-depth analysis of the grid. As will be readily understood, the electrical signal could be converted to a digital signal.

[00188] In one embodiment, the light source is a micro-LED and a characterization of micro-LED temperature behavior and development of a signal compensation approach may be required as will be understood by one skilled in the art. It may be sufficient to simply calibrate the micro-LED at different temperatures. If the behavior of the micro-LED as a function of temperature and time is reproducible, the calibration approach may be appropriate.

[00189] Calibration tests can be carried out to determine the impact of other parameters such as temperature, presence of other electrical fields in the area, electromagnetic noise, magnetic fields, etc., on the reading obtained by the voltage sensor. A calibration adjustment can then be done on the measured voltage to increase accuracy of the reading.

[00190] In one embodiment, the present voltage sensor may be used for residential installations which use voltages as low as 100 V. It could also be used for power line measurements for voltages as high as hundreds of kV.

[00191] In one embodiment, the voltage sensing assembly may further comprise a return-path circuit that is connected in parallel to the light source. The return-path circuit can be provided to allow the current to travel and to protect the light source from accidental peak currents. For example, the return-path circuit comprises a diode such as a transient voltage diode. It should be understood that the return-path circuit may comprise a component other than a diode or comprise components in addition to a diode. [00192] While in the above description, it is referred to a current source generating a

DC current for powering a light source, it should be understood that the current source may generate an AC current. Since the AC or DC current generated by the current source is predefined and the response of the light source to the AC or DC current generated by the current source is known (i.e., the amplitude of light in time generated by the light source in response to the AC or DC current generated by the current source is known), it is possible to determine the amount of light generated by the light source that is caused by the AC current resulting from the movement of charges.

[00193] In comparison to prior art optical voltage sensors which only comprise a floating conductor and a light source, the present voltage sensor assembly provides at least some of the following advantages.

[00194] In one embodiment, the present voltage sensor assembly provides a better precision and has an internal reference signal to maintain the calibration.

[00195] In one embodiment, the bandwidth the voltage sensor is improved. In one embodiment, an optical sensor comprising no current source presents a bandwidth of about 20kHz. By adding a current source to the optical voltage sensor, the bandwidth may be increased to up to 200kHz.

[00196] In one embodiment, the optical signal emitted by the voltage sensor is substantially linear for any point of the waveform. In this case, the raw signal is close to correspond to a perfect derivative and it is easier to treat the raw signal to obtain the waveform of the voltage.

[00197] In an embodiment in which an LED is used, a single optical fiber may be used. Therefore, the read-out unit only needs a single canal of detection.

[00198] With respect to an optical voltage sensor comprising no source of current, the present sensor may have reduced dimensions. [00199] The embodiments of the invention described above are intended to be exemplary only. The scope of the invention is therefore intended to be limited solely by the scope of the appended claims.