Method and apparatus for monitoring generation and transmission of electrical power

This invention concerns a procedure for monitoring the transmission of electrical power being transmitted via one or more electrical high voltage lines, where the magnetic field from at least one of the conductors in the high voltage line is measured with the aid of at least one sensor coil device as a function of the current that is being conducted by the high voltage line(s). Furthermore, the invention concerns a device for measuring the magnetic field in connection with a high voltage transmission conductor for electricity in order to measure and monitor the generation and transmission of electricity with a single sensor coil device placed in the magnetic field for the induction of a sine-like current in the coil.

Today, there are many types of apparatus and methods which enable the measurement and monitoring of the amount of power that is being generated by a power station that is connected to the high voltage transmission network.

The best known methods for the implementation of such measurement require access to the physical installation that is connected to the power station or the transmission conductor. The owner, or operator, of these installations can control and/or prevent access to the installations, and is therefore able to prevent any external player from using available technology to directly measure and monitor the amount of current that is being transmitted via a given transmission conductor or the amount of electrical power that is being generated by a given power station. Information on electricity transmission, generation, etc. is of relevance for players that are involved in the commercial purchasing and sale of electricity on the open market. Today, some of the information relating to electricity generation is published, but often on an aggregated basis and at a national level.

In addition to the better known methods for the direct measurement of current as referred to above, Genscape, Inc., a company which has its head office in the USA, has developed a technology that enables the amount of current that is being transmitted via a given high voltage transmission conductor and the path that the current is following to be determined. Inductive equipment is used for this purpose, i.e. equipment with no direct connection to the transmission conductor. The solution that is used, which is described in more detail in EP patent application 01 927 053.7, enables the measurement and monitoring of a power station in a way which was not previously possible.

Genscape's technology is based on measurement of the magnetic field around a given power conductor via one or more measuring stations located close to, but not in physical contact with, the power conductor. Through this technology, it has been made possible to calibrate the equipment according to the amount of current that is being transmitted via the abovementioned conductor. In addition, the electrical field on the conductor is measured for use in combination with the magnetic field in complex algorithms in order to determine the path that the current is following. The equipment that is used receives its power supply from a solar cell panel and there is wireless communication with a central unit which performs data- based calculations. The distribution of calibrated data takes place via an internet-based, password-protected payment service to third parties. Genscape's technology is complicated, and the solution depends on being able to see the relationship between the magnetic fields and the electrical field in order to determine the path that the current is following in the transmission conductor being measured, and a complicated calculation algorithm must be used for this purpose. The power supply from the solar cell panel is not particularly well suited to Nordic conditions, as some of the power generation takes place in areas which during the winter can be without sun for extended periods of time and in which snow can completely or partially cover the panel.

The CHK Engineering PTY LTD, which has its head office in the USA, has developed a technology for the purpose of identifying faults in a measured high voltage conductor by using an air coil which surrounds the high voltage conductor and a condenser to measure the electrical field. The solution that is used, which is described in more detail in PCT patent application WO Al 00/62084, enables the detection of large changes in the amount of current that is being transmitted through the high voltage conductor.

CHK Engineering's technology requires considerable dynamics in the system, and uses an amplifier which has AGC (Automatic Gain Control). They also use a coreless measuring coil in order to achieve the large dynamics. Physical access to the high voltage network is also required. The technology cannot detect the path along which the current is being transmitted, or when the current direction reverses.

The purpose of the invention is to measure and monitor transmission conductors and power generation without any direct connection to the transmission conductors or the power station's

own meters. More precisely, the invention is intended to determine the magnitude and any change in the direction of the electrical current that is being transmitted on a particular high voltage electric transmission conductor, and thus also make it possible to determine the amount of electrical power that is being generated by a particular power station which is connected to the high voltage transmission network. A further aim is to overcome a number of the deficiencies of known solutions.

The information concerning power supply that the invention facilitates will be of relevance for all the players in a deregulated power market, which exists throughout most of Europe today. This will lead to greater transparency, which is essential if a market is to function as intended, and will be of both commercial and socio-economic interest.

Unlike known technology, the invention does not use solar cell technology, but instead uses technology which provides a power supply to a measuring station which can be left unmanned for at least one year at a time, independent of the weather conditions in relation to the known solutions.

The technology is also based on only measuring the magnetic field, and uses standard technology. This makes the measuring equipment cheaper and also makes the calculation of current quantity and determination of the current path considerably simpler.

The procedure in accordance with the invention is not limited to the collection of information as referred to above, as it is also suitable for the transmission and further processing of the information that is collected. The invention also enables the transmission of collected data from the remote measuring units to a central database, with each individual measuring unit monitoring a particular transmission conductor or conductors. The data that is collected is processed further in the central database in order to calculate both the amount and direction of current flow in each individual monitored transmission conductor. The processed data can be further analysed and collected to determine the net electricity generation, i.e. the power being generated, by one or more power generation plants that are connected to the high voltage transmission network.

The apparatus in accordance with this invention primarily covers a measuring unit which collects the necessary information in order to determine the amount of electrical current that is

flowing in a particular transmission conductor that is being monitored. More specifically, a measuring station in accordance with the invention will be installed as a fixed installation close to a high voltage electrical transmission conductor, but still at an appropriate physical distance from it. The measuring unit primarily consists of a measuring instrument which measures the density of the magnetic field in connection with the transmission line, on either a periodic or a permanent basis.

In accordance with the invention, the procedure is characterised by measuring the magnetic field generated by the current in the high voltage line and determining the current direction in the high voltage line through the same measured value supplied by a sensor coil device placed in the magnetic field, letting a 180-degree phase change in the measured value at a particular time as a function of reversed current direction in relation to an anticipated phase for the measured value at the abovementioned time of measurement cause a reversed current direction in the high voltage line to be signalled, and transferring information concerning the magnetic field and current direction in the high voltage line to an external central data processing unit.

In accordance with the invention, the apparatus is characterised by a processor which receives the induced current as a readable measured value and as a function of the actual magnetic field for the transmission conductor in question and the current being transmitted by the transmission conductor, together with a device in the processor which also detects and warns of any 180-degree phase change in the measured value at a particular time as a function of a reversal of the current direction in the transmission conductor in relation to an anticipated phase for the measured value at the abovementioned time.

In accordance with additional design forms of the apparatus, the process is equipped to continually monitor the sine curve of the magnetic field related to the alternating current being transmitted, and in the event of a 180-degree phase change in the sine curve to signal a reversed current direction in the high voltage transmission conductor that is being measured. Furthermore, the apparatus has an amplifier for the stepped increase of measured data to a representative numerical value, and an internal memory for the storage of the abovementioned numerical values. In addition, the apparatus contains a transmitter/receiver to transfer the representative numerical values from the internal memory to a dedicated central processing unit.

These and additional design forms of the procedure and the apparatus in accordance with the invention are described in the description below with reference to the enclosed drawings, where a non-exhaustive design example is presented in more detail.

Figure 1 shows a perspective sketch of the preferred design for the unit for measuring and monitoring electrical power generation and transmission lines in accordance with the invention.

Figure 2 shows a schematic overview of the content of the unit which is shown in Figure 1, and equipment that is necessary to perform the necessary functions for the invention.

Figure 3 is a block diagram which illustrates the preferred procedure for information handling in connection with a measured magnetic field in accordance with the invention.

Figure 4 shows a circuit diagram for a preferred amplification and filtration circuit for the magnetic field measurement in connection with the measuring unit as shown in Figure 1.

Figure 5 schematically shows an overview of the service which will be made possible through the invention.

Figure 6a shows the principle of the sine curve that is derived from the magnetic field, while Figure 6b shows the phase displacement that occurs when the current changes direction.

Figure 7 shows a plot of a measured magnetic field, in addition to publicly available statistics, for a 42OkV transmission line between Halden in Norway and Skogsseter in Sweden.

This invention is based on the measurement and monitoring of electrical power generation, and the transmission of detected information concerning the electricity transmission in connection with one or more power generation units. This is achieved by measuring and collecting data that is related to the amount of electricity that is being transmitted via one or more transmission lines which are connected to a particular electrical transmission network and to one or more electricity generating units. Data-based analysis of this data with the aid of simple algorithms enables the calculation of the amount of electricity that is being generated

by the abovementioned generating units which are connected to the high voltage transmission network.

Electrical power is distributed over the majority of the high voltage transmission network in a three-phase form, where each of the phases is transmitted via a separate conductor. In this description, "transmission conductor" will be used to refer to the three separate conductors. Each of these separate phases (the conductors) generates its own time-varying magnetic field. The three phases are out of phase hi relation to each other by one third of a cycle, so that the sum of the magnetic fields will to all intents and purposes be zero if all three phases are collected closely together in a transmission conductor. The conductors in the overhead cable network are separated from each other an adequate distance, partly because of the large voltage differences between the conductors that occur at all times and partly to reduce mutual magnetic field effects between the conductors. According to established theory, including the Biot-Savart Law concerning magnetic fields, any point in the air around these three phases will contain a magnetic field which is determined by a particular set of factors. These factors include the number of kilovolts for which the transmission conductor is designed, the amount of current that is being transmitted in the conductor, the distance between the phases in relation to the measurement point and the Earth's magnetism at the measurement point in question.

The apparatus in accordance with the invention covers an individual sensor to measure both the a) magnetic field as a separate factor, and b) variations in the alternating current which can be derived from measurement of the magnetic field as another factor.

Equipment that is located close to, but at a safe physical distance from, the transmission conductor will be referred to as the "measuring unit".

As Figure 1 shows, measuring unit 1 will first and foremost consist of a locking, water-tight casing 1', made from non-magnetic material, e.g. hard plastic. The casing contains a magnetic field meter, a processing unit, communication components and batteries, including a power supply and data transmission components, as explained in more detailed in connection with Figures 2 and 3. Furthermore, casing V will be attached to post 1" which ensures that the casing is at all times located above the maximum statistical snow depth. The post is secured to

the ground either via a base that has been drilled into the ground or via a concrete base embedded in the ground.

Figure 2 schematically shows an overview of the components inside the measuring unit's casing 1. The magnetic field from the transmission conductor will be monitored by coil 2 which consists of a large number of coil windings, e.g. coil 2, with wound copper wire with 27,000 windings, which is located around an "I" core of transformer plates, 3. The magnetic field induces a current in the measuring coil and the current is filtered and a resistance is applied. The voltage across this resistance is a function of the magnetic field and is for example measured in millivolts (mV). In this description, the term "magnetic field measurement" is used with regard to the abovementioned measurement. As for our purposes we do not need to measure more than one magnetic field, this single coil is sufficient. It is however extremely important that the necessary magnetic field sensitivity is achieved. This is largely determined by the physical location of the measuring unit. In order to facilitate calibration and installation and to optimise the magnitude of the signals that are received if the measuring unit has to be located at a relatively large distance from the transmission conductor, the magnetic field meter has therefore been placed in the building on rotating disc 4, which is supported by supporting disc 5, which enables changes to be made to the angle settings of the magnetic field meter when the measuring unit is out in the field. Data from magnetic field meter 2 will be transmitted to data processing unit 6, which filters 9 and amplifies 10 the data and stores it in internal memory 6'. The filtration and amplification will be considered in a separate section below in relation to Figure 3. Furthermore, data processing unit 6 also contains logic 15, transmission unit 12, GPS positioning system 16 and power supply system 7. If required, GPS unit 16 can be omitted if GPS coordinates are programmed into unit 6 when the unit is installed in situ. Power supply system 7 distributes the necessary power supply to the various units from batteries which are included in the system.

The location of measuring unit 1 will normally be most favourable immediately below one of the outermost conductors in the transmission line, and ideally where the nearest conductor is located at a relatively short distance from measuring unit 1. However, many factors will in practice determine where the unit is installed. In any case, the unit must be located sufficiently close to the transmission line to enable the measuring unit to be sufficiently sensitive to measure the magnetic field with sufficient sensitivity. In order to assure the quality of the data that is measured, several measuring units can be installed which measure

the same transmission conductor. This could for example be appropriate if the conductors are arranged in a large span, or where the conductors frequently physically swing as a result of the weather conditions.

Figure 3 shows a block diagram of the external field-installed unit 1, in accordance with the invention. The measuring unit generally consists of magnetic field meter 2, as explained above in relation to Figure 2, and filter 9, which filters out background noise. The measurements are fed via amplification module 10 to achieve the required sensitivity level, so that the signals are suitable for conversion from analogue to digital signals via separate A/D converter 11. The amplification is reviewed in more detail in relation to Figure 4. Furthermore, battery connection 7 is specified with a battery pack, e.g. of the Lithium D-CeIIs type, real-time clock 14, logic on a dedicated circuit board in microprocessor 15, GSM modem 16, with integrated GPS unit and communication antenna 17. As mentioned previously, the GPS unit component may be omitted if the GPS co-ordinates for unit 1 or another identifier are programmed into data processing unit 6.

Figure 4 shows the basic construction of the amplification model 10. The signal Ul which is received is the induced current from magnetic meter 2, and is amplified in stages, e.g. eight stages. If the signal measures less than 0.5Vpp on the input, the first amplification stage is connected in. This represents an amplification of 2x with feedback resistance R3 and generator resistance R4. If the signal is still below 0.5Vpp, the next stage is connected in, which gives 4x amplification. This is done by connecting R5 in parallel with R4 via Ql. The process can continue in this way until the maximum amplification of 128x is achieved. The precise amplification factor for each amplification stage is calculated because the signal strength must be multiplied by the chosen factor before it is presented. As the amplification factor is increased, generator resistances R5 to RlO are added gradually in parallel. This is done to reduce the effect of the varying accuracy of the resistances.

If we return to Figure 3, at this point central microprocessor 15 will receive the amplified signals in analogue form. The first thing that happens is that the signals are converted to digital form via A/D converter 11. The digital signals are then tested to check whether the latest measured values which are stored in the microprocessor's memory 6' correspond to the measured values which were transmitted to the central unit on the previous occasion. If there is a discrepancy between the latest measured values and the stored measured values, the logic

will generate a data string which contains, among other things, the latest measured values and the precise time of measurement received from real-time clock 14. The latest measured values will be stored in the processor and forwarded to central unit 22 (see Figure 5), as a GPRS message via GSM modem 16 and antenna 17. Microprocessor 15 will await confirmation that the message has been received by the central unit. K confirmation is not received, the processor can generate a new message based on the last data that was sent, and send it as an SMS message to central unit 22 via unit 16 and antenna 17. Processor 15 includes a phase detector 15' for the respective measurements from the transmission lines and is equipped to detect and warn of any 180-degree phase change in the measured value at a particular time as a function of a change in the current direction in the transmission line in relation to the expected phase for the measured value at the abovementioned time.

Figure 5 schematically shows how the service is constructed and dependent on many sub- processes. In data processing unit 22, data-based analysis of information from unit 1 will be carried out. This is described in more detail below. Thereafter, provided that all, or at least most, of the transmission lines 19 of a power station 18 are measured and analysed in accordance with this invention, the net electricity generation of the power station concerned can be determined via a simple summation of the current in the connected transmission lines. Furthermore, this information, whether it concerns one or more power stations or power lines, can be communicated wirelessly 21 from unit 1 via antenna 20 to receiver and processor 23 in data processing unit 22, and from there to third parties 28-1....28n. Unit 22 contains database 24 for unprocessed data, a calibration unit with quality control 25, a database with the fully processed data set 26, and internet application 27. The distribution to third parties can primarily take place via a password-protected internet site 27, which can also contain a link to database 26 with physical and electrical parameters for different transmission lines and generating plants. The data relating to power generation and distribution which is of interest to third parties can thus be made available via a standard web browser, such as Netscape Navigator or Microsoft Internet Explorer. Alternatively, distribution can take place via SMS, a permanently dialled line or similar.

As a secondary element, it will be possible to update and re-program microprocessor 15 in measuring unit 1 from central unit 22 via the two-way communication 21, which can be located between unit 1 and centre 22.

In order to return to the data-based analysis in data processing unit 22, the data that is received will be automatically converted to the amount of electricity (and therefore power) which is being transmitted, and whether the current flow has reversed on the transmission line in question. More specifically, a number of factors which determine the amount of current which is passing through a particular transmission line will be constant, or almost constant, depending on the amount of current that is actually flowing through the line. For each transmission line, it is possible to determine the magnitude, expressed in kilovolts (kV), either through observation or through publicly available information. The previously mentioned Earth's magnetism will be a constant which does not affect the measurement because it represents a static level which does not induce current in the measuring coil. Other relative constant factors are fluctuations in the transmission conductors due to wind and weather conditions in general, and small changes in the relationship between the measured magnetic field and the actual current flow due to temperature changes and general weather conditions. These factors will have some effect on the accuracy of the fully processed data, but the error percentage will be small and can be eliminated from the data through calibration when the necessary empirical data has been obtained. The only variables that are not constant, independent of the time and weather, will be the amount of current that is being transmitted through the transmission line and the direction of the abovementioned current flow. Data that is received from the measuring unit enables these variables to be calculated.

Following a calibration period, it will be possible to have a computer program calculate both the amount of current, and the power that is therefore being transmitted, and the direction of the current flow.

The method for performing this calculation has two components. Both components are ultimately calculated in the central data processing unit 22 on the basis of data received from measuring unit 1.

The first component calculates the amount of current that is being transmitted in the transmission line 19 that is being measured. Microprocessor 15 uses the input signal from measuring coil 2 and filters it at a frequency of 50Hz through the coil forming part of an oscillatory circuit. If there is a frequency deviation of 50Hz, e.g. by +/- 3%, it must be assumed that the oscillatory circuit nevertheless enables satisfactory detection, even though in such a situation it could be signalled to the central data processing unit that there is a

frequency deviation in the transmission, which could occur in the event of high current loads. In this way, the amplification of the signal increases considerably, and the curve shape becomes smooth. The smoothed value is transmitted to central unit 22 for further processing. By using empirical data, together with information concerning the transmission conductor and- the power station that is connected to it, it is possible by plotting measured values against calculated actual flow via the transmission line to find the linear relationship between the two data sets. This linear relationship can then be used in an algorithm which automatically recalibrates the data that is received to the actual amount of transmitted power, expressed in Megawatts (MW), which will then be used to calculate actual power generation of the power station in question. In connection with this., reference is made to the enclosed Figure 7, which shows a plot of a measured magnetic field of 42OkV on a transmission line between Halden in Norway and Skogseter in Sweden. The measurements were taken over a period of 24 hours on 28 February 2007. The left-hand axis shows the power in Megawatts (MW) and is related to plotted data 29 from Statnett. The right-hand axis shows amplified measured values from measuring unit 1, which are related to plotted 30 data marked "Ell measured value". Statnett's data is published with an hourly resolution, which explains the distinct shifts every hour. In this case, the relationship between EiI measured values and the amount of MWs being transmitted via the power line varies little as a result of Statnett's coarse data resolution.

Figure 6a schematically shows a modified sine curve 31 related to the magnetic Field in the respective phase of power line 19 in the normal situation and in a situation in accordance with Figure 6b where the current flow, represented by curve 32, has reversed, with dashed curve 31 shown for comparative purposes. The first component in the calculation related to the current quantity was referred to previously in the description. The second component determines whether the direction of the αmtni Sow has changed since the previous measurement. Ih order to determine this, the sine curve in the alternating current is monitored. This can be monitored as it is proportional to the current flow in the transmission conductor. The curve is stable during normal operation and can be subject to marginal fluctuations over time. 50.0Hz is the standard frequency. The normal maximum permitted fluctuation deviation is +/-0.1Hz before the central network operators) intervenes to stabilise the frequency. The trend in the sine curve during normal operation is schematically illustrated in Figure 6a through curve 31. If the current flow in the transmission conductor reverses, the frequency will remain the same in the electrical field. However, the magnetic field will be different. The magnetic field will change direction, i.e. it will experience a phase displacement of 180° if the transmission

direction in the transmission cable reverses. This means that, as we have a permanently installed measuring unit, a 180° change would be apparent from the phases of the sine curve that we are monitoring. This is illustrated in Figure 6b through curve 32. As each measurement is taken, microprocessor 15 will therefore compare the sine curve with previously stored and expected curves in the process in relation to a time axis. If the processor sees a change in time from one curve to the next of 10ms, it will indicate that the phase has turned 180°. The processor synchronises itself with the signal and is able to filter the signal through the use of software so that interruptions and noise can be permitted at the instant the current reverses.

If such a change takes place, a message will be generated which will be sent to central unit 22. The message concerning a change in current direction will not state the direction in which the current is actually flowing, simply that it has changed direction. This means that in order to specify the path that the power transmission is following, the direction in which the current was flowing at a particular time must be known. This status is altered each time a message is received indicating that the current direction has reversed. In order to then determine the direction that the current is flowing in, the measured direction is synchronised with available public data, experience and observation. After this, the system will follow the same pattern, i.e. it will synchronously follow each change in power transmission.

In order to determine how much current a power station 18 is generating, it will be necessary to monitor most, and preferably all, of the transmission lines 19 that are connected to the power station concerned. Provided that the measurements have already been calibrated, so that the amount of current flowing through the transmission conductor and the direction in which the current is being transmitted are known, the function of the measured transmission conductors will give an indication of the current being generated by the power station concerned. In certain cases, some power stations may be a net importer of current due to the pumping of water into reservoirs during the summer.

Instantaneous net generation can be expressed as follows:

AP=JE-J I where P= generation, JE?= export from the power station and /=import to the power station.

Example: the Sima power stations in the municipality of Eidfjord in Norway. This power station is connected to the national grid via two three-phase 42OkV cables, with one cable going to Aurland and one to Dagali in Norway.

Practical example 1: after calibration, measurements of the Sima- Aurland transmission line indicate an export of 800MW, while measurements of the Sima-Dagali line indicate an import of 300MW, i.e. the net generation at the moment of measurement is 500MW (800-300=500)

Practical example 2: Sima- Aurland indicates an export of 200MW ₅ while Sima-Dagali indicates an export of 400MW, i.e. a net generation of 600MW (600-0=600)

Practical example 3: Sima- Aurland indicates an import of 750MW, while Sima-Dagali indicates an export of 650MW, i.e. the power station is a net importer/user of IOOMW for the pumping of water (750-650=100).

As is apparent from the above, the invention will result in a much clearer solution compared with previous known solutions, in that the invention is based on measuring the magnetic field only and is based on empirical measurements, known parameters and operating patterns for the power station concerned, thereby finding simple relationships between the magnetic field and the actual generated current, which can be used to improve the information used in decision-making by players that are involved in commercial buying and selling on the open market, and resulting in a general improvement in transparency in the abovementioned market.