[0001] The present invention relates to a capacitive unit for local power factor correction and a system comprising multiple capacitive units.

[0002] Inductive loads are used widely in commercial and industrial settings, for example in the form of electric motors and transformers used in compressor and refrigeration systems, ventilation and air conditioning, motor drives of industrial machines and others. The cost and environmental impact of operating such inductive loads is directly correlated to their power consumption. It is thus desirable to improve the efficiency of power transmission and consumption of inductive loads. [0003] The power factor of an AC electric power system is generally considered a measure of efficiency of the system. The power factor is defined as the ratio of real or active power used by the load and apparent power transmitted to the load. An AC electric power system comprising an overall inductive load typically has apparent power greater than real power. This is due to energy that is stored in the inductive load, in the form of a magnetic field required to operate the inductive load, and returned to the source. The power factor of such a system is less than 1 or unity. The “wasted” or useless power lost to energising the magnetic field of the inductive load is also referred to as reactive power. The AC current waveform in such an inductive load is out of phase, and lags, the AC voltage waveform. The reactive power does not contribute to the useful power output of the inductive load, but adds to the power transmitted to the inductive load and thus increases the environmental impact and cost of operating the inductive load.

[0004] Power factor correction units may be used to improve the power factor and reduce the reactive power of an AC electric power system. Such power factor correction units compensate for the lagging current induced by the inductive load by creating a leading current, for example by using capacitive loads. A capacitive load gives rise to a negative reactive power, effectively cancelling the positive reactive power of an inductive load. However, conventional power factor correction units and systems do not provide the required flexibility and customizability to achieve optimized power factor correction over a range of inductive load conditions, and are not easy and convenient to operate. In practice, inductive loads may switch off, fail or break down, change in inductivity or be replaced by other loads. Furthermore, the configuration of inductive loads varies widely among existing electric power systems, such that an off-the-shelf unit may not optimally correct the power factor. Maintenance and monitoring of multiple capacitive units requires an operator to separately access each capacitive unit, making such tasks complicated and time- consuming. [0005] W02020/039207 A1 discloses a power factor correction unit that improves on such known systems.

[0006] There is a general need for further improvements to power factor correction units.

[0007] According to a first aspect of the invention there is provided a power factor correction system for locally applying power factor correction to a multi-phase inductive load, the power factor correction system comprising: a capacitive unit comprising one or more capacitive modules, wherein each capacitive module comprises a multi-phase capacitive load; one or more electronic switching modules, wherein each electronic switching module is arranged to connect a capacitive module in parallel to the multi -phase inductive load; and a control system configured to control the switching time of each electronic switching module in dependence on a voltage difference between at least one of the one or more capacitive modules and one or more power supply cables of the multi-phase inductive load.

[0008] According to a second aspect of the invention, there is provided a power factor correction method for locally applying power factor correction to a multi-phase inductive load, the power factor correction method comprising: measuring the voltage, current and/or power in one or more power supply cables of a multi-phase inductive load; determining to apply, in dependence on the voltage, current and/or power measurement, a power factor correction by electronically switching in, or electronically switching out, a capacitive load in parallel to the multi-phase inductive load; controlling the switching time of the capacitive load in dependence on a voltage difference between at least one of the one or more capacitive modules and the multi-phase inductive load.

[0009] The invention is described below, by way of example only, with reference to the drawings, in which:

[0010] Figure 1 is a schematic diagram showing an example of how the capacitive unit of the present invention may be connected to an AC electric power system;

[0011] Figure 2 schematically shows the capacitive unit with three capacitive modules;

[0012] Figure 3 shows a detailed schematic of an embodiment of the capacitive unit of Figure 2; [0013] Figure 4 shows a schematic diagram of a three-phase AC power supply, a three-phase inductive load, and a power factor correction system according to an embodiment;

[0014] Figure 5 shows a schematic diagram of detuned reactors of a detuned reactor system as well as a capacitive module of a capacitive unit according to an embodiment;

[0015] Figure 6 is a schematic diagram of a switching unit according to an embodiment;

[0016] Figure 7 is a schematic diagram of the configuration of thyristors in a thyristor module according to an embodiment; and [0017] Figure 8 shows the determination of a switching time in dependence on measured voltages according to an embodiment.

[0018] The following description is merely exemplary in nature and is not intended to limit the scope of the present invention, which is defined in the claims. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features.

[0019] Embodiments of the present invention may be used for power factor correction of an inductive load in an AC electric power system, in which electric power is supplied to the inductive load by an AC electric power source. Preferably, embodiments are used in a multi-phase AC electric power system, comprising a multi-phase inductive load and a multi-phase AC electric power supply. Further preferably, embodiments are used in a three-phase AC electric power system, comprising a three-phase inductive load and a three-phase AC electric power supply. The capacitive unit will in the following be described in terms of its preferable application in a three- phase AC electric power system. However, the capacitive unit described in the following could be readily adapted for application in other multi-phase AC electric power systems, such as two-phase, four-phase or higher-phase AC electric power systems, or in a single-phase AC electric power system.

[0020] Embodiments may improve on the power factor correction unit that is disclosed in W02020/039207 Al. The entire contents of W02020/039207 A1 are incorporated herein by reference. An overview of the disclosure in W02020/039207 Al is provided below before embodiments of the invention are described.

[0021] Figures 1 to 3 of the present document correspond to Figures 1 to 3 of W02020/039207 Al. [0022] Figure 1 shows an AC electric power system comprising a power supply 300 and an inductive load 200. The inductive load 200 is connected to the power supply 300 via phase cables 201a, b, c. Specifically, Figure 1 shows a three-phase AC electric power system, comprising a three-phase AC electric power supply 300 and a three-phase inductive load 200 connected thereto via three phase cables 201a, b, c. A capacitive unit 100, specifically shown as a three-phase capacitive unit 100 in Figure 1, is connectable in parallel to the inductive load 200. This ensures that the capacitive unit 100 can be easily installed in existing electric power systems without the need to disconnect the inductive load 200 from the power supply 300. The capacitive unit 100 is connected in parallel to the inductive load 200 via connection lines 101a, b, c. All components of the capacitive unit 100 may be connected to the phase cables 201a, b, c at the same location. Alternatively, the components of the capacitive unit (such as capacitive modules 105, 105’, 105”) may separately be connected to the phase cables 201a, b, c. The capacitive unit 100 may be connected to the inductive load 200 either locally or at the distribution side of an inductive load 200 that, for example, comprises several smaller inductive loads. This allows the capacitive unit 100 to be installed by the consumer of electric power, or the user of the inductive load 200, to allow for local power factor correction and reduce the cost and environmental impact of the inductive load 200.

[0023] The capacitive unit 100 may be located in a housing, such as a glass reinforced plastic (GRP) housing. All components of the capacitive unit 100 may be enclosed by the housing. The capacitive unit 100 may be a stand-alone unit. The capacitive unit 100 thus can be delivered and installed as a single unit.

[0024] Figure 2 shows an implementation of the capacitive unit 100 comprising three capacitive modules 105, 105’, 105”. The three capacitive modules 105, 105’, 105” are connected in parallel. Each of the capacitive modules 105, 105’, 105” comprises a capacitive load 110, 110’, 110” and a contactor 120, 120’, 120”. The capacitive unit 100 further comprises a central control unit 130.

The central control unit 130 controls the contactors 120, 120’, 120”, so as to open and close the contactors 120, 120’, 120”. Although three capacitive modules 105, 105’, 105” are shown in Figure 2, the capacitive unit 100 may include fewer or more capacitive modules. For example, the capacitive unit 100 may include only one capacitive module 105, or the capacitive unit 100 may include only capacitive modules 105 and 105’. Alternatively, one or more additional capacitive modules maybe connected in parallel to the three capacitive modules 105, 105’, 105” in the capacitive unit 100.

[0025] Each of the capacitive modules 105, 105’, 105” maybe identical. Alternatively, different capacitive modules 105, 105’, 105”, for example including capacitive loads 110, 110’, 110” with different capacitances, may be used. Each of the capacitive modules 105, 105’, 105” may be chosen from a set of standard capacitive modules. It may also be possible to customize each of the set of standard capacitive modules. This allows the capacitive unit 100 to be highly customizable to match the inductive load 200. Changes to the inductive load 200 may be matched easily by adding further capacitive modules to the capacitive unit 100, exchanging one of the capacitive modules 105, 105’, 105”, or changing the capacitive load 110, 110’, 110” of one or more of the capacitive modules 105, 105’, 105”. This makes the capacitive unit 100 highly flexible to hardware changes in the inductive load 200. Using three capacitive modules 105, 105’, 105” ensures a high flexibility of the capacitive unit 100, while maintaining a simple construction. Using more than three capacitive modules 105, 105’, 105” may further improve the customizability and flexibility of the capacitive unit 100. Using less than three capacitive modules 105, 105’, 105” may make the construction of the capacitive unit 100 simpler. Using three capacitive modules 105, 105’ 105” to be an effective trade-off between simplicity and flexibility of the capacitive unit 100. [0026] A detailed schematic diagram of the capacitive unit 100 of Figure 2 is shown in Figure 3. The capacitive unit 100 comprises three capacitive modules 105, 105’, 105”. Each of the three capacitive modules 105, 105’, 105” comprises the capacitive load 110, 110’, 110”, the contactor 120, 120’, 120”, a charge indicator 160, 160’, 160”, and a module over-current protection element 170, 170’, 170”. The capacitive unit 100 further comprises a central control unit 130, a power supply unit 140, a varistor bank 150, and a thermal conditioning system comprising a thermostat 180 and a fan 182. The central control unit 130 comprises a plurality of ports, for example four ports as shown in Figure 3. Each of the plurality of ports is connected to a respective one of a plurality of functional modules 134, 134’, 136, 138, such as relay modules 134, 134’, a modem 136 and a connection module 138. The central control unit 130 comprises a display 132, the relay modules 134, 134’, a time delay element 135, the modem 136, an input device 137, and the connection module 138 for connecting to one or more other capacitive units 100’. The one or more other capacitive units 100’ may be identical to the capacitive unit 100, except for the functional modules of the central control unit 130. The capacitive unit 100 may be a master capacitive unit 100, including a master control unit 130, and the one or more capacitive units 100’ may be one or more slave capacitive units 100’, including slave control units. The slave control units may not include a modem 136. A plurality of probes comprising current measurement devices 133, 133’, 133” maybe connected to the central control unit and measure the voltage and current of each phase of the multi-phase inductive load 200. The central control unit 130 receives current measurements of the current flowing through phase cables 201a, b, c from current measurement devices 133, 133’, 133” and further receives voltage measurements of the voltage at the phase cables 201a, b, c.

[0027] The capacitive module 105 will be described in the following. Each of the three capacitive modules 105, 105’, 105” may correspond to the capacitive module 105 described below, and comprise identical or similar components to the capacitive module 105 described below, unless stated otherwise.

[0028] The contactor 120 is for switching capacitive loads, such as capacitive load 110. The contactor 120 may comprise two switching terminals. A holding voltage, or control voltage, may be applied to the switching terminals. The contactor 120 is closed, so as to connect the capacitive load 110 to the inductive load 200, when the holding voltage applied to the switching terminals of the contactor 120 exceeds a pre-set minimum voltage. The contactor 120 is open, so as to disconnect the capacitive load 110 from the inductive load 200, when the holding voltage applied to the switching terminals is below the pre-set minimum voltage.

[0029] The contactor 120 may be of a type that achieves minimal arcing on the coil contacts. For example, the contactor 120 may be an AF30-30-30 by ABB ®. The holding voltage that is applied to the switching terminals of the contactor 120 may be in the range from 20 to 500V, preferably in the range from 20 to 30V, for example about 24V. The contactor 120 may support an AC electric voltage with a frequency in the range from 25 to 400 Hz, preferably in the range from 40 to 70 Hz. The contactor 120 may support a peak voltage of up to 690V, preferable in the range from 100 V to 300V. The contactor 120 may be switchable, between an open and closed state, at a frequency in the range from 0.01 to 1 Hz, preferably from 0.04 to 0.4 Hz.

[0030] The holding voltage across the switching terminals of the contactor 120 is provided by the power supply unit 140 and controlled by the central control unit 130. The central control unit 130 is connected to current measurement devices 133, 133’, 133” and includes a relay module 134 comprising one or more switches. The current measurement devices 133, 133’, 133” maybe placed around respective phase cables 201a, b, c. The phase cables 201a, b, c provide electric power to the inductive load 200. The current measurement devices 133, 133’, 133” may measure the current (such as a reactive current) in the phase cables 201a, b, c. Each of the current measurement devices 133, 133’, 133” may be a current transformer. The central control unit 130 may receive current measurements from the current measurement devices 133, 133’, 133”.

[0031] The relay modules 134, 134’ comprise one or more switches, for example two switches. Each relay module 134, 134’ may be used to control a fixed maximum number of capacitive modules 105, 105’, 105”, for example up to two capacitive modules as in the embodiment of Figure 3. The one or more switches of each relay module 134, 134’ are individually controllable or switchable by the central control unit 130. Each switch of the relay modules 134, 134”, when closed, may create a closed electric circuit including an output side of the power supply unit 140 and the switching terminals of a respective contactor 120, 120’, 120”. Each switch of the relay modules 134, 134’, when closed, applies the holding voltage to the contactor 120, thereby closing the contactor 120. The central control unit 130 may thus control the multi-phase capacitive load applied to the multi-phase inductive load, for example by selectively opening and closing the switches of the relay modules 134, 134’. Such control may be in dependence on the current, the voltage or the power in at least one phase cable 201a, preferably all (three) phase cables 201a, b, c, providing electric power to the multi-phase inductive load. The dependence on the current, the voltage or the power herein includes any dependence on measurable characteristics of the current, voltage or power, such as the magnitude of the current, voltage or power or the phase difference in current, voltage or power between two or more of the phase cables 201a, b, c. Dependence on the power may be dependence on the real, reactive or apparent power.

[0032] For example, when the current measurements received by the central control module 130 from the current measurement devices 133, 133’, 133” fall below the pre-determined threshold, or when voltage measurements received by the central control module 130 fall below a corresponding threshold, or when the power (for example the reactive power) in at least one phase cable, preferably all (three) phase cables, falls below a corresponding threshold, the central control module 130 may open the switches of the relay modules 134, 134’. This interrupts the electric circuit including the output side of the power supply unit 140 and the switching terminals of the contactors 120, 120’, 120”, breaking the holding voltage applied at the switching terminals of the contactors 120, 120’, 120”. The contactors 120, 120’, 120” may thus disconnect the capacitive loads 110, 110’, 110” of the respective capacitive modules 105, 105’, 105” from the inductive load 200.

[0033] The threshold, for example the pre-determined threshold, is stored or pre-set in the central control unit 130. The (pre-determined) threshold may, for example, be input into the central control unit 130 by a user using the input device 137. Alternatively, the threshold may be communicated to the central control unit 130 from an external device. The (pre-determined threshold) may be freely adjustable by a user. The (pre-determined) threshold may be determined, for example, based on the reactive current output of the capacitive load 110 of the capacitive module 105. The (pre determined) threshold may correspond to a current in the range from 0.2 times to 1.5 times, preferably from 0.9 times to 1.1 times, the reactive current output of the capacitive load 110. For example, if the reactive current output of the capacitive load 110 is 90 A, the value of the pre determined threshold may be 90 A (provided the inductive load 200 consumes only a reactive current component), such that the capacitive load 110 is disconnected from the inductive load 200 when the current in a phase cable 201 a, b, c to the inductive load 200 falls below 90 A. Alternatively, the (pre-determined) threshold may also correspond to a voltage or power value in the range from 0.2 times to 1.5 times, preferably from 0.9 times to 1.1 times, the voltage or power output of the capacitive load 110. The power value may be calculated by the central control unit 130 based on the current and voltage measurements.

[0034] The central control unit 130 may individually open the switches of the relay module so as to break the holding voltage applied to the switching terminals of the respective contactor 120, and open the contactor 120. The central control unit 130 may open an electric circuit formed between the power supply unit 140 and the switching terminals of the contactor 120. This disconnects the capacitive load 110 from the inductive load 200. It can be avoided that the capacitive load 110 acts as a reactive power generator when the reactive power consumed by the inductive load 200 falls below the reactive power generated by the capacitive load 110. This improves the power factor of the AC electric power system, thereby reducing the power consumption and the environmental impact.

[0035] The time delay element 135 may delay, by a time delay, controlling the contactor 120 to connect the multi-phase capacitive load 110 in parallel with the multi-phase inductive load 200 after disconnecting the multi -phase capacitive load 110 from the multi-phase inductive load 200. Put another way, the time delay element 135 implements a delay period after disconnecting the capacitive load 110 in which the central control unit 130 is prevented from closing the contactor 120. The time delay may be pre-determined and pre-set in the time delay element 135. The time delay may be input into the central control unit 130 by a user using the input device 137. Alternatively, the time delay may be communicated to the central control unit 130 from an external device. The time delay may be freely adjustable by a user. The time delay ensures that residual charges, or latent energy, may be dissipated from the capacitive load 110 before re-connecting the capacitive load 110 to the AC electric power system. Connecting the capacitive load 110 before residual charges are dissipated may damage the capacitive unit 100. Implementing the time delay reduces the risk of damage to the capacitive unit 100.

[0036] The time delay element 135 may, for example, be a implemented in software running on the central control unit 130. The time delay may be set such that residual charges are allowed to dissipate from the capacitive load 110 after opening the contactor 120 and disconnecting the capacitive load 110. For example, the time delay may be set such that at least more than 90%, or preferably more than 99%, of residual charges are dissipated. The time delay may be calculated based on the RC time constant of the capacitive load 110, or each capacitor resistor pair of the capacitive load 110. For example, the time delay may be larger than twice, and preferably larger than three times, the RC time constant of the capacitive load 110 or each capacitor resistor pair of the capacitive load 110. For example, if the RC time constant of the capacitive load 110 is in the range from Is to 60s, the time delay may be in the range from 2s to 120s, preferably from 3s to 180s.

[0037] A problem with the power factor correction unit disclosed in W02020/039207 A1 is that, due to the time required to discharge the capacitors, the response time of the power factor correction unit to a change of load conditions may be longer than 60 seconds. This is acceptable for substantially static, or relatively slow changing, load conditions where few switching operation occur each hour. The power factor correction unit disclosed in W02020/039207 A1 may therefore be suitable for applications such as large machine tools and drives with high duty ratios. [0038] Embodiments provide a power factor correction system that may have a faster response time to a change in load conditions than the power factor correction unit disclosed in W02020/039207 A1. The response time to change of load conditions may only be a few milliseconds. The power factor correction system according to embodiments may therefore be used with rapidly fluctuating loads, such as elevator systems, injection moulding systems and many other applications. The power factor correction system according to embodiments may therefore be more dynamic than the power factor correction unit disclosed in W02020/039207 Al.

[0039] The power factor correction unit disclosed in W02020/039207 Al comprises electro mechanical contactors for switching in, and switching out, capacitances for applying a power factor adjustment to a load. The power factor correction system of embodiments differs by alternatively using thyristor modules 601 to electronically switch in, and switch out, capacitances for applying a power factor adjustment to a load. As will be explained in more detail later, the use of thyristor modules 601 avoids the problem of time delays being incurred due to the need for residual charges in the capacitors to be dissipated.

[0040] The power factor correction system of embodiments may also differ from the disclosure in W02020/039207 Al by comprising detuned reactors for reducing the harmonics in the system. [0041] The power factor correction system of embodiments may also have a modular structure that differs from the disclosure in W02020/039207 Al.

[0042] Figure 4 schematically shows a three-phase AC power supply 300, a three-phase inductive load 200, and a power factor correction system according to an embodiment. The three-phase AC electric power supply 300 and three-phase inductive load 200 may be connected to each other by three phase cables 201a, b, c. The power factor correction system may comprise a control system 401, a detuned reactor system 402 and a capacitive unit 403. The control system 401, the detuned reactor system 402 and the capacitive unit 403 may all be provided as separate modules.

[0043] The capacitive unit 403 may be similar to, or the same as, as any of the capacitive units 100 disclosed in W02020/039207 Al. The capacitive unit 403 may comprise a plurality of capacitive modules 407. Each capacitive module 407 may be similar to, or the same as, any of the capacitive modules 105, 105’, 105” disclosed in W02020/039207 Al. The capacitive unit 403, and/or any of the capacitive modules 407, may be configured according to any of the arrangements shown in Figures 4a to 4c of W02020/039207 Al. The outputs of the capacitive unit 403 may all be connected to one or more of the cables 201a, b, c of the AC electric power system via the detuned reactor system 402 and the control system 401.

[0044] Each capacitive module 407 may comprises a multi-phase capacitive load. The capacitive modules 407 of the capacitive unit 403 may all have the same total capacitive loads, i.e. kVar capability. Alternatively, two or more of the capacitive modules 407 of the capacitive unit 403 may all have different total capacitive loads, i.e. different kVar capabilities. Advantageously, a larger range and/or granularity capacitances may be applied by the capacitive unit 403 if the capacitive modules 407 of the capacitive unit 403 have different total capacitive loads. The capacitive unit 403 may be able to provide up to 24kVar, which may be sufficient for most applications. The capacitive unit 403 may be configured to provide more than 24kVar, such as 48kVar, as may be required in some large applications.

[0045] The detuned reactor system 402 may be configured to reduce the magnitude of any harmonics that may be present and help to prevent any resonances occurring.

[0046] The control system 401 may comprise a switching unit 405, a sensor unit 404 and a control unit 406. The switching unit 405 may be configured to connect one or more capacitive modules 407 in the capacitive unit 403 to one or more of the cables 201a, b, c of the AC electric power system. The sensor unit 404 may be configured to measure one or more of the voltages, currents and/or relative phases of the cables 201a, b, c of the AC electric power system. The sensor unit 404 may comprise any of the features disclosed in W02020/039207 A1 for measuring one or more of the voltages, currents and/or relative phases of the cables 201a, b, c of the AC electric power system.

[0047] The control unit 406 may be configured to control the switching unit 405, as well as any other part of the power factor correction system. The control unit 406 may receive, for example in real-time, current and voltage measurements, obtained by the sensor unit 404, of each of the phase cables 201a, b, c connected to the multi-phase inductive load 200. The control unit 406 may use the received data to control the power factor correction system. The control unit 406 may also output data to a user interface and/or an external device. For example, it may output data on the operation of the power factor correction system.

[0048] An advantage of the power factor correction system of embodiments is its modular design. The control system 401, detuned reactor system 402 and capacitive unit 403 may all be provided as separate units that may be in different locations. This aids the implementation of the power factor correction system in sites where there are space restrictions. For example, the control unit 406, detuned reactor system 402 and capacitive unit 403 may each be located on different walls of the same room of a building. In addition, the components of the modular system can be easily replaced and this aids the upgrading and maintenance of the system.

[0049] Figure 5 shows detuned reactors 501 of the detuned reactor system 402 as well as a capacitive module 407 of a capacitive unit 403 according to an embodiment. [0050] The detuned reactor system 402 may comprise a plurality of detuned reactors 501. The number of detuned reactors 501 may be the same as the number of cables received by the detuned reactor system 402 from the capacitive unit 403. As shown in Figure 5, each detuned reactor 501 may be a reactor that is provided on a cable between the capacitive unit and the control unit 406. Each detuned reactor 501 may comprise an inductor. The reactance of an inductor increases with frequency so inductors have a large impedance with high frequency signals. The detuned reactor system 402 may therefore substantially block high frequency signals, in particular harmonics, in the cables between the capacitive unit 403 and the control system 401.

[0051] The inductance value of each reactor may be selected such that the resonant frequency is less than 90% of dominant harmonic in the spectrum. For example, if the 5 ^th harmonic is dominant in the spectrum of a 50Hz system, the reactor may form part of a series LC circuit having resonant frequency at 90% of 250Hz. If the resonant frequency of the LC circuit is less than 225Hz, the reactor may be categorised as a detuned reactor 501.

[0052] Detuned reactors 501 are commercially available components. Detuned reactors 501 may be purchased from, for example, Schneider Electric™. A product range may comprise detuned reactors 501 with properties from, for example, 6 to 100 kvar. The detuned reactors 501 maybe available in the most common tunings, such as 135, 190 and 210 Hz for network voltage of 400/415V@50Hz. Each detuned reactor 501 of the detuned reactor system 402 may be selected according to the capacitor(s) in the capacitive module 407 that it is associated with.

[0053] The advantages of using a detuned reactor system 402 may include one or more of: the substantial elimination of harmonic amplification; the increased life of capacitors due to the reduced voltage and thermal stress from harmonics; the prevention of the unnecessary fuse blowing and/or circuit breaker tripping; the reduction of overheating of any transformer(s), busbar(s) 603, cables, switchgear etc. caused due to harmonic amplification; the reduction of the harmonic current in the electrical supply system; the harmonic problems created by non-linear loads being reduced; and the power factor may be improved. In particular, the use of detuned reactors 501 may prevent harmonic amplification, which may be caused by resonance, and thereby reduce, or substantially avoid, the risk of overloading the capacitive modules 407 of the capacitive unit 403. The use of detuned reactors 501 may significantly reduce the magnitude of voltage and current harmonic distortion that may occur and thereby reduce voltage fluctuations that may result in equipment malfunction or failure. The detuned reactor system 402 may also help to protect all of the components of the capacitive unit 403 against switching inrush, which may otherwise damage the components of the capacitive unit 403 (such as capacitors, circuit breakers and contactors). [0054] Although there are a number of advantages of using a detuned reactor system 402, embodiments also include a power factor correction system that comprises the capacitive unit 403 and control system 401 of embodiments, but no detuned reactor system 402. That is to say, there may be no detuned reactors 501 provided in the cables between the capacitive unit 403 and the control system 401. The use of a detuned reactor system 402 is therefore optional.

[0055] The switching unit 405 of the control system 401 is described in more detail below. Figure 6 is a schematic diagram of the switching unit 405 according to an embodiment. The switching unit 405 comprises a plurality of thyristor modules 601, a plurality of connection units 602 and a busbar 603.

[0056] The number of thyristor modules 601 may be the same as the number of capacitive modules 407 in the capacitive unit 403. Each thyristor module 601 may be connected to a different respective one of the capacitive modules 407 in the capacitive unit 403.

[0057] As shown in Figure 6, the inputs to each thyristor module 601 may comprise three cables that extend between the thyristor module 601 and the detuned reactor system 402. The outputs from each thyristor module 601 may comprise three cables that extend between the thyristor module 601 and a connection unit 602. The connection unit 602 may connect each of the cables to a cable of a busbar 603. The busbar 603 may comprise three cables that are connected to each of the connection units 602 as well as the cables 201a, b, c of the AC electric power system. Each connection unit 602 may be configured to directly connect each cable from a thyristor module 601 to a cable of the busbar 603. Each connection unit 602 may comprise one or more fuses or switches that may break the direct connection of each cable from a thyristor module 601 to a cable of the busbar 603, as may be required for safety or other purposes.

[0058] Figure 7 is a schematic diagram of the configuration of thyristors in a thyristor module 601 according to an embodiment. Each thyristor module 601 may comprise one or more thyristors for electronically switching a capacitive module 407 in, and out, to thereby vary the applied capacitance by the power factor correction system. The number of thyristors comprised by each thyristor module 601 may be the same as the number of cables that the thyristor module 601 receives from the detuned reactor system 402. Alternatively, the number of thyristors in the thyristor module 601 may be less than the number of cables that the thyristor module 601 receives from the detuned reactor system 402. For example, there may be one less thyristor than the number of cables. As shown in Figure 7, there may be three cable that pass through the thyristor module 601. Thyristors may be provided in the path of two of the cables and one of the cables may not have a thyristor provided in its path. Accordingly, for each thyristor module 601, one of the cables from the detuned reactor system 402 may always be electrically connected to the busbar 603 and therefore at the voltage of one of the cables 201a, b, c of the AC electric power system. The thyristors of each thyristor module 601 may be provided by a silicon controlled rectifier (SCR) circuit.

[0059] Each thyristor module 601 may comprise a communication module 604. The communication module 604 may allow data to be communicated between each of the thyristor modules 601 and the control unit 406 of the control system 401. The communicated data may be, for example, control data, performance data and/or sensor data. The control data may be, for example, data for controlling when each thyristor is switched on and off. The performance data may, for example, comprise information on any errors that may be detected in the operation of a thyristor module 601, or any other component of the power factor correction system. The sensor data may comprise, for example, voltage, current and/or temperature measurements. The communication between the thyristor modules 601 by the communication modules 604 may be over a serial communication system, such as an RS485 bus. Each thyristor module 601 may also may also have a further communications interface, such as an optical IR port, for direct programming and diagnostics of the thyristor module 601 by external devices.

[0060] The operation of the thyristor modules 601 is described below with reference to Figure 8. [0061] The voltage on each of the cables output from the capacitive system may be measured. The voltage may be measured by one or more of voltage sensors in one or more of the capacitive system, the switching unit 405, the thyristor modules 601 and the detuned reactor system 402. The measured voltage on each of the cables output from the capacitive system may be communicated to the control unit 406 of the control system 401. The voltage on a cable output from the capacitive unit 403 may be substantially the same as the voltage on the same cable at a port of a thyristor module 601. When the thyristor switch is open, the voltage on the cable output from the capacitive unit 403 may be falling relatively slowly, at a rate that is dependent on the time constant of the capacitive module 407.

[0062] The voltage on each of the cables 201a, b, c of the AC electric power system may also be measured and communicated to the control unit 406 of the control system 401. The voltage on a cable 201a, b, c of the AC electric power system may be substantially the same as the voltage at a port of a thyristor module 601. The voltage on one of the cables 201a, b, c of the AC electric power system may be a relatively fast changing voltage. In a typical mains power supply the voltage will have a frequency of 50Hz.

[0063] When a decision is made to switch in, or out, an electrical connection between one of the capacitive modules 407 and the cables 201a, b, c of the AC electric power system, the time at which the switching is performed may be dependent on the measured voltages. [0064] Figure 8 shows the voltage 802 on one of the cables output from a capacitive module 407 as well as the voltage 801 on the corresponding cable 201a, b, c of the AC electric power system.

Prior to time T, the thyristors of a thyristor mode 601 in the electrical connection path is open and the capacitive module 407 is not electrically connected to the corresponding cable 201a, b, c of the AC electric power system. The voltage on the cable 201a, b, c of the AC electric power system is changing much faster than that of the cable output from the capacitive module. Embodiments include the control unit 406 being configured to control the thyristor to close, and thereby electrically connect the capacitive module 407 to the cable 201a, b, c of the AC electric power system, when there is substantially no difference between the measured voltages 801, 802. The thyristors of the thyristor module 601 may therefore closed at time T. Advantageously, the capacitive module 407 may be switched in without waiting for its charge to dissipate. The switching in of a capacitive module 407 can therefore be performed faster than known techniques. Switching in the capacitive module 407 when there is substantially no potential difference between the cable output from a capacitive module 407 and the cable 201a, b, c of the AC electric power system also reduces the stress that is applied to the capacitive module 407.

[0065] Accordingly, the control unit 406 may be configured to receive a voltage 802 measurement of one of the cables output from a capacitive module 407, that may be substantially the same as the voltage at a port of an open thyristor. The control unit 406 may also be configured to receive a voltage 801 measurement of a cable 201a, b, c of the AC electric power system, that may be substantially the same as the voltage at another port of the open thyristor. The control unit 406 may be configured to determine a time T for closing the thyristor when the differences between the measured voltages 801, 802 is less than a predetermined threshold. The predetermined threshold may be, for example, 0.1V. All of the thyristors may therefore be switched without generating a substantial amount of stress on the capacitive modules 407 of the capacitive unit 403. The switching time of each thyristor in a thyristor module 601 may be the same for all of the thyristors in the thyristor module 601. Alternatively, each of the thyristors in the thyristor module 601 may be individually switched in dependence on the measured voltages at its ports.

[0066] The current on each of the cables output from the capacitive unit 403 may also be measured. The current may be measured by one or more of current sensors in one or more of the capacitive unit 403, the switching unit 405, the thyristor modules 601 and the detuned reactor system 402. For example, each thyristor module 601 may comprise a current transformer and/or current sensor on at least one, and preferably all, of the cables that pass through it. These may help to protect the capacitive modules 407 in the event of any overcurrents, such as if there is a distortion of the voltage waveform. The current monitoring may also be used for advanced diagnostics of the thyristor modules 601 and/or the capacitive unit 403. The incorporation of a current transformer and/or current sensor in each thyristor module 601 also allows the determination and monitoring of properties such as the residual power of the capacitive unit 403, voltages, currents, heatsink temperatures, capacitor temperatures, THDI, operating hours and maximum values for any signalling of anomalies on the system (e.g. blown fuse) on the capacitive unit 403 or on a thyristor module 601.

[0067] Each thyristor module 601 may also be configured with protection thresholds. For example, there may be a protection threshold for one or more of: a maximum current, a maximum voltage, a maximum heatsink temperature, a maximum capacitor temperature, a maximum total harmonic distortion (THDI), a maximum current asymmetry and a minimum residual capacitor power. If a protection threshold is exceeded, then a critical alarm may be triggered that may, for example, prevent the operation of a thyristor module 601.

[0068] Each thyristor module 601 may also have a built-in fan, or fans, and the thyristor module 601 may comprise sensors for measuring and reporting the status of the fan(s). For example, the fan(s) temperature and supply current may be monitored so that a failure of the fan may be quickly detected.

[0069] Each thyristor module 601 may be, for example, the DCTLA4800090 as made by Lovato electric (see https://www.lovatoelectric. com/ -THYRISTOR-MODULE, -9KVAR-AT-480VAC,- RATED-OPERATING-VOLT AGE-400.. 480V AC, -WITH-CURRENT- CONTROL/DCTLA4800090/snp, as viewed on 12 ^th February 2021).

[0070] Any of the capacitive unit 403, the switching unit 405, the thyristor modules 601 and the detuned reactor system 402 may also comprise additional sensors to voltage and current sensors.

For example, there may be thermometers for measuring temperatures.

[0071] The control unit 406 may be configured to communicate with all of the components of the power factor correction system. In particular, the control unit 406 may be in communication with all of the thyristor modules 601 and receive data from all of the sensors. The control unit 406 may control the switching of all of the thyristors in the thyristor modules 601. The control unit 406 may also be in communication with a user interface of the control system 401. The control unit 406 may also be in communication with one or more communication ports of the control system 401 for communicating with external devices. The communication with external devices may be over a wireless interface. The control unit 406 may have substantially the same, or similar, properties to the central control unit 130 as disclosed in W02020/039207 Al.

[0072] An external device that the control unit 406 may be configured to communicate with may be, for example, a computer desktop or a mobile device, such as a mobile phone, a tablet or a laptop computer. The external device may be located remotely from the control unit 406, for example in a different room or building than the control unit 406. The control unit 406 may send operating data, such as real-time operating data or historic operating data, of the multi-phase inductive load 200 to the external device, such that the operating data can be manipulated and/or displayed on the external device. Similarly, the operating data of all capacitive modules 407 may be provided to the external device. The external device may store or display the operating data received from the control unit 406. A user or operator may monitor the operating data of the multi-phase inductive loads 200 and/or capacitive unit 403 from a remote location using the external device. The user may control any aspect of the power factor correction system from the external device.

[0073] There may be a number of advantages of using thyristor modules 601 as switches according to embodiments. For example, the switching time may be faster than if electro-mechanical switches are used, and this allows the power factor correction to be applied quickly. The switches may have a longer lifetime than electro-mechanical switches. The switching may be performed without transients. That is to say, the use of thyristor modules 601 may reduce the peaks of current (inrush currents from capacitors) or voltage due to the zero-crossing switching capability of the thyristor modules 601, and this may improve the power quality of the entire system. There may be a reduction of reactive power and this provides saving costs in the form of less reactive current costs, less energy losses, etc. There may be a reduction of flickering and voltage drops on the line supply, and this improves the voltage stabilization. The absence of moving mechanical components also allows the thyristor modules 601 to operate silently. This makes them particularly suitable for installation in environments which may require substantially silent operation (e.g., hotels, banks, cinemas, hospitals...). There may be an improved utilization of the energy distribution throughout the system due to the reduction of power peaks. There may be a reduction in the cost of distribution and transmission systems, i.e., cable cross-sections, etc., due to the avoidance of peaks of current. The power factor correction system may have a longer service life, due to the contactless switching at both the switching element and the capacitors. The safety of power factor correction system may be improved because the use of highly stressed mechanical contactors is avoided.

[0074] The control system 401 is configured to support dynamic, i.e. fast, power factor correction as is appropriate in systems with a rapidly varying reactive load. The control system 401 may comprise a user interface. The user interface may comprise, for example, a backlit graphic LCD display, arrange to display text in a number of different languages. The control system 401 may also comprise a wireless communication port, such as an optical IR communication port. This may improve the electrical safety of the power factor correction system because there is no need to disconnect the a user interface panel power supply to connect with the control system 401. The control system 401 may be configured to communicate with external devices such as PCs, smartphones and tablets through either USB or Wi-Fi. This may be used for programming the power factor correction system, diagnosing any faults in the power factor correction system, and data transfer between an external device and the control system 401.

[0075] The control system 401 may be configured to communicate with and control a large number of thyristor modules 601 via the RS485 bus. For example, the control system 401 may communicate with, and control, over thirty thyristor modules 601. The control system 401 may monitor the status of each of the thyristors in each of the thyristor modules 601. The control system 401 may receive measurement data from within each thyristor module 601, such as measurements of temperatures, currents, voltages, residual powers, THDI, operating hours, and other properties. The received data from the thyristor modules 601 may be displayed, or communicated to an external device, by the control system 401.

[0076] Embodiments therefore provide a number of advantages over power factor correction systems that use electro-mechanical switches for controlling the switching in and out of the capacitive unit 403.

[0077] The power factor correction system of embodiments may include any of the techniques as disclosed in W02020/039207 Al. For example, the capacitive unit 403 may comprise a modem and a thermal conditioning system. The thermal conditioning system may comprise a thermostat and a fan. The modem may be a 3G, 4G, 5G or higher generation modem, for example. The modem may be a wireless communication device.

[0078] The control system 401 may receive, for example in real-time, current and voltage measurements of each of the phase cables 201a, b, c connected to the multi -phase inductive load 200. The control system 401 may calculate operating data, such as real-time operating data and historic operating data, of the multi-phase inductive load 200 based on the voltage and current measurements. Such operating data may include some or all of real power data, reactive power data, apparent power data, power factor data, harmonic frequency data, voltage data and current data. The control system 401 may also compile historic operating data and display, and/or output, historic operating data. This allows a user to observe operation of any component of the power factor correction system over an extended period of time. The control system 401 may be powered by a connection to phase cables 201a, b, c. The connection may include suitable fuses to protect the control system 401 from surge currents.

[0079] A problem with known power factor correction systems is that their operation is substantially fixed from when they are installed on a site. The efficiency of the power factor correction system therefore decreases when changes occur in the power factor correction system or the load.

[0080] According to known techniques, during the planning of the installation of the power factor correction system on a site, a power quality analysis may be performed to determine the requirements of the power factor correction system. The power quality analysis may determine requirements such as KVar. The results of the power quality analysis are then used to determine the configuration and capability of the power factor correction system that is installed on the site. The power factor correction system may consist of multiple capacitor banks, with each capacitor bank consisting of a single capacitor and control gear.

[0081] The power quality analysis is performed by a power quality analyser. The power quality analyser is not part of the power factor correction system and is removed before, or soon after, the installation of the power factor correction system. Over time, the capacitors of the power factor correction system will degrade and the loads may change. If a clearly apparent fault occurs that results in the power factor correction system being substantially replaced, then a further power quality analysis may be performed. However, fault conditions are not always apparent. Accordingly, no further power quality analysis may performed after the initial installation of the power factor correction system. The installed power factor correction system may therefore no longer be appropriate given the changes that have occurred over time. In particular, harmonics may occur that are not detected. The harmonics may reduce the efficiency of the system and cause damage.

[0082] Embodiments may differ from known power factor correction systems both in their capability and in how, and when, a power quality analysis is performed.

[0083] In the power factor correction system according to embodiments there may be, for example, nine or more capacitive loads 110, 110’, 100” in the capacitive unit 100. The power factor correction system therefore has substantial capability to change the applied capacitive load and to correct for any changes to the system that occur over time.

[0084] The power factor correction system according to embodiments may also perform a power quality analysis, that determines power quality parameters, without requiring a separate power quality analyser. Furthermore, embodiments include the power quality analysis automatically being repeatedly preformed. The power quality analysis may be performed continuously or periodically. The power quality analysis may be automatically performed by the control system 401 and/or control unit 406. All of the data required for performing the power quality analysis may be automatically transmitted to the control system 401 and/or control unit 406. In particular, the control system 401 and/or control unit 406 may receive real-time operating data of the multi -phase inductive load 200 and all of the capacitive modules 407. The control system 401 and/or control unit 406 may also receive temperature data for components within the power factor correction system and/or components in the load, such as motors.

[0085] The power quality analysis may determine the current KVar requirements and, in particular, may include performing a harmonic analysis. A harmonic analysis is able to detect abnormal harmonic conditions. For example, a harmonic analysis may determine that the THDi is about 35- 42%, whereas the guideline level of THDi is about 5-8%. Such an excessive THDi level both decreases efficiency, by increasing power consumption, and may also cause an overheating risk of a cable and this could cause a fire. The power quality analysis may also determine an abnormal condition based on received temperatures. In particular, a high level of harmonics may cause components to overheat. This is a particular problem for motors because a 10°C over temperature may reduce the operating life of a motor by up to 50%. Overheating in components that is caused by high harmonic levels is also dangerous because it is a fire risk.

[0086] Embodiments include the operation of the power factor correction system being automatically controlled, by the control system 401 and/or control unit 406, in dependence on the determinations made by the power quality analysis. The KVar output of the power factor correction system may be constantly monitored and changes to the operation of the capacitive unit 100 made to maintain it at an appropriate level. This improves the effectiveness of the power factor correction system.

[0087] Embodiments include the control system 401, and/or control unit 406, automatically generating alerts and/or alarms whenever an abnormal condition is detected by the power quality analysis. The alerts and/or alarms may also be generated in dependence on general reporting requirements that may be set. For example, alerts and/or alarms may be generated in dependence on one or more of a maximum allowed THDi being exceeded, the power factor being below a predetermined threshold, the power factor being above a predetermined threshold, the voltages and/or currents being above/below predetermined thresholds, a temperature of a component of the system being above a predetermined threshold, and the date for a routine maintenance approaching. [0088] The alerts and/or alarms may be displayed on a user interface of the power factor correction system, and/or provided by a warning sound. As described earlier, control system 401 and/or control unit 406 may be configured to communicate with a remote external device. The external device may be, for example, a computer desktop or a mobile device, such as a mobile phone, a tablet or a laptop computer.

[0089] Embodiments include the alerts and/or alarms, that are automatically generated when an abnormal condition is detected by the power quality analysis, being communicated to the external device. For example, an email or text message may be automatically generated and sent to report a fault condition, a measured parameter being outside of its expected range and/or other type of notification. The email or text message may be sent to a remotely located person who is responsible for supervising the power factor system. The external device may therefore remotely control the power factor correction system, remotely monitor the power factor correction system, and/or receive alerts/alarms from the power factor correction system. The external device may be located anywhere in the world that has a mobile telephone reception and/or an Internet connection. [0090] As described earlier, an advantage of the power factor correction system of embodiments is its modular design. The control system 401, detuned reactor system 402 and capacitive unit 403 may all be provided as separate units that may be in different locations. The power factor analysis may automatically determine and report components of the modular system that need to be replaced, or upgraded, for the efficient operation of the power factor correction system. Improvements to the power factor correction system may therefore be easily made.

[0091] Embodiments alternatively include the external device automatically and repeatedly, continuously or periodically, performing the power quality analysis instead of, or in addition to, the control system 401 and/or control unit 406. The control system 401 and/or control unit 406 may be configured to obtain all of the data required for the power quality analysis and communicate this to the external device. The external device may generate commands for controlling the power factor correction system based on the power quality analysis and send the commands to the control system 401 and/or control unit 406 to thereby automatically control the power factor correction system. [0092] Embodiments also include a number of modifications and variations to the techniques described above.

[0093] In particular, in the above-described embodiments, the thyristor modules 601 are comprised by the control system 401. Embodiments also include an alternative implementation in which the thyristor modules are comprised by the capacitive unit 403 or the detuned reactor system 402. For example, one or more of the thyristor modules 601 and/or capacitive modules 407 may comprise a wireless modem, or other communications device, for communication with the control unit 406.

The communication may be according to the techniques disclosed in W02020/039207 Al.

[0094] Although the use of thyristors in thyristor modules 601 has been described throughout the present application, embodiments more generally include the use of any electronic switch instead of thyristors. The thyristor modules 601 may therefore more generally be referred to as electronic switching modules 601.

[0095] Throughout embodiments, the power factor correction system has been described in relation to a three-phase AC electric power system, with a three-phase power supply 300 and a three-phase inductive load 200. However, embodiments include the power factor correction system also being used in single-phase, two-phase, four-phase or higher phase AC electric power systems.

[0096] Embodiments include the following numbered clauses.

[0097] Clause 1 : A power factor correction system for locally applying power factor correction to a multi-phase inductive load, the power factor correction system comprising: a capacitive unit comprising one or more capacitive modules, wherein each capacitive module comprises a multi phase capacitive load; one or more electronic switching modules, wherein each electronic switching module is arranged to connect a capacitive module in parallel to the multi-phase inductive load; and a control system configured to control the switching time of each electronic switching module in dependence on a voltage difference between at least one of the one or more capacitive modules and one or more power supply cables of the multi-phase inductive load.

[0098] Clause 2: The power factor correction system according to clause 1, wherein each electronic switching module is a thyristor module.

[0099] Clause 3: The power factor correction system according to clause 2, wherein each thyristor module comprises one or more thyristors.

[00100] Clause 4: The power factor correction system according to clause 3, wherein: each thyristor module comprises three cables configured to connect a three-phase capacitive load with a three-phase inductive load; each thyristor module comprises two thyristors, each of which is arranged on a different one of the three cables; and a thyristor is not arranged on one of the three cables.

[00101] Clause 5: The power factor correction system according to any of clauses 2 to 4, wherein each thyristor module comprises a communications module for communication with the control system.

[00102] Clause 6: The power factor correction system according to clause 5, wherein: there are a plurality of thyristor modules; and each communications module of a thyristor module is configured to communicate with a communications module of another thyristor module.

[00103] Clause 7: The power factor correction system according to any preceding clause, wherein: the capacitive unit comprises a plurality of capacitive modules; and at least two of the capacitive modules have different capacitive loads.

[00104] Clause 8: The power factor correction system according to clause 7, wherein the number of capacitive modules is between 2 and 12, preferably 4 to 6.

[00105] Clause 9: The power factor correction system according to any preceding clause, wherein the control system comprises: a switching unit that comprises the one or more electronic switching modules; a control unit configured to communicate with the switching unit and to control each electronic switching module; and a sensor unit configured to measure, and transmit to the control unit, the voltages, currents and/or powers on one or more power supply cables to the multi phase inductive load.

[00106] Clause 10: The power factor correction system according to clause 9, wherein the switching unit comprises: a connection unit; and a busbar comprising a plurality of cables; wherein: the connection unit is configured to electrically connect each cable from an electronic switching module to a cable of the busbar; and each cable of the busbar is connected to a power supply cable of the multi-phase inductive load.

[00107] Clause 11: The power factor correction system according to clause 9 or 10, wherein the control unit is configured to control the multi-phase capacitive load applied to the multi-phase inductive load by the capacitive unit in dependence on the current, the voltage and/or the power in at least one power supply cable to the multi-phase inductive load.

[00108] Clause 12: The power factor correction system according to any of clauses 9 to 11, wherein the control unit is configured to: receive a first voltage measurement of a power supply cable of the multiphase inductive load; receive a second voltage measurement of a capacitive module; determine a voltage difference between the first and second voltage measurements; and determine the switching time of an electronic switching module in dependence on the voltage difference being less than a threshold value.

[00109] Clause 13: The power factor correction system according to clause 12, when dependent on clause 3, wherein the control unit is configured to control all of the thyrisors in a thyristor module to switch at the same time.

[00110] Clause 14: The power factor correction system according to clause 12, when dependent on clause 3, wherein the control unit is configured to individually control the switching time of each of the thyrisors in a thyristor module.

[00111] Clause 15: The power factor correction system according to any of clauses 9 to 14, wherein the control unit is configured to control the switching of one or more electronic switching modules such that the switching of an electronic module, in response to a change in inductive load being detected, occurs within less than 20ms, preferably less than 10ms, and more preferably less that 5ms, of the change in inductive load being detected.

[00112] Clause 16: The power factor correction system according to any of clauses 9 to 15, wherein the control unit is configured to wirelessly communicate operating data to an external device of the control system; wherein the operating data comprises one or more of real power data, reactive power data, apparent power data, power factor data, harmonic frequency data, voltage data and current data. [00113] Clause 17: The power factor correction system according to clause 16, wherein the external device is a computer desktop or a mobile device, such as a mobile phone, a tablet or a laptop computer.

[00114] Clause 18: The power factor correction system according to clause 16 or 17, wherein the control unit is configured to receive instructions from the external device, wherein the instructions include: switching one or more capacitive modules of the capacitive unit on or off; and/or controlling one or more electronic switching modules; and/or changing the current, the voltage and/or the power in at least one power supply cable to the multi-phase inductive load by changing the one or more capacitive modules electrically connected to the multi-phase inductive load.

[00115] Clause 19: The power factor correction system according to any preceding clause, wherein the multi-phase inductive load is a three-phase inductive load and the multi-phase capacitive load is a three-phase capacitive load.

[00116] Clause 20: The power factor correction system according to any preceding clause, wherein the power factor correction system is a modular system; and the control system and capacitive unit are separate modules of the modular system.

[00117] Clause 21 : The power factor correction system according to any preceding clause, further comprising a detuned reactor system; wherein the detuned reactor system comprises a plurality of reactors; and each of the reactors are arranged on a cable between a capacitive module and the control system.

[00118] Clause 22: The power factor correction system according to clause 21, when dependent on clause 20, wherein the detuned reactor system is a separate module of the modular system than the control system and capacitive unit.

[00119] Clause 23: A power factor correction method for locally applying power factor correction to a multi-phase inductive load, the power factor correction method comprising: measuring the voltage, current and/or power in one or more power supply cables of a multi -phase inductive load; determining to apply, in dependence on the voltage, current and/or power measurement, a power factor correction by electronically switching in, or electronically switching out, a capacitive load in parallel to the multi -phase inductive load; controlling the switching time of the capacitive load in dependence on a voltage difference between at least one of the one or more capacitive modules and the multi-phase inductive load.

[00120] Clause 24: The power factor correction method according to clause 23, wherein the method is performed in a power factor correction system according to any of clauses 1 to 22. [00121] The foregoing description of the preferred embodiments has been provided for the purposes of illustration and description. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but where applicable may be interchangeably used in combination with other features to define another embodiment, even if not specifically shown or described. The description is therefore not intended to limit the scope of the present invention, which is defined in the claims.