CHECKING SYSTEM FOR CONTROL MEASUREMENT OF ENERGY MEASURING SYSTEMS

Abstract: The invention relates to a checking system for control measurement of an energy measuring system connected in a high-voltage network. Such an energy measuring system (2) is used to measure the energy consumed in a plant, for instance a distribution plant, connected to the high-voltage network. The energy measuring system comprises an energy meter (23), a normal current (21) connected to the energy meter and a normal voltage (22) connected to the energy meter. The checking system (1) is mobile and comprises a high-voltage transformer to be connected to the normal voltage of the energy measuring system, a heavy-current transformer to be connected to the normal current of the energy measuring system, a normal-current-generating means connected to the heavy-current transformer, a normal-voltage-generating means connected to the high-voltage transformer and adapted to generate a normal voltage, and a comparator unit (8), which is connected to the normal-current-generating means and the normal-voltage-generating means and which is adapted to be connected to the energy meter. The comparator unit is adapted to determine a normal value of the consumed energy and to compare the normal value with the measured value of the energy meter and determine the difference therebetween. The difference is a measure of the total error of measurement of the energy measuring system.

Description: CHECKING SYSTEM FOR CONTROL MEASUREMENT OF ENERGY MEASURING SYSTEMS Field of the Invention The present invention relates to checking systems for control measurement of energy measuring systems, more specifically to checking systems for control measurement, carried out in the field, of energy measuring systems operating in high-voltage environment. Background of the Invention Energy measuring systems operating in high-voltage environments are installed by a power distributor in distribution plants or with customers connected to the high-voltage network of the power distributor (network owner) . The energy measuring system measures the energy taken from the high-voltage network. To enable the power distributor (network owner) and the supplier to charge the correct fee, it is important that the energy measur¬ ing system makes a correct measurement of the consump¬ tion. Therefore there is a need of checking, in a very accurate fashion, the actual energy measuring system and its individual components. Today there is no technique for checking the entire energy measuring system at the same time, i.e. the entire coupling of all the components included, such as the energy meter, measuring transformers, measuring lines and connections. The available methods of checking are instead directed to the individual components, or more specifically the individual measuring transformers which transform the high currents and voltages of the high-vol¬ tage system to low levels such that they can be handled by an energy meter (Wh meter). The usual procedure is to go to the energy measuring system, disconnect the high-voltage network, dismount the measuring transformer, take it to a checking laboratory and there connect it to a high-voltage-generating plant in the same manner as it is connected in the field. A laboratory measuring transformer that is used for check¬ ing voltage and current is very exact. On the secondary side of the current or voltage measuring transformer, absolute values are measured, and a correction number, or error of measurement, is determined. This way of checking is associated with a number of drawbacks. It gives but a picture of the errors of the individual measuring transformers and not of the total errors of the entire energy measuring system. It is a time-consuming procedure to dismount the measuring trans¬ formers, transport them to and from the laboratory and mount them again. During dismounting and mounting, the high-voltage network must be disconnected. A further prior-art measuring system is based on a very accurate normal measuring transformer, which is arranged on a trailer and thus is mobile. The normal mea¬ suring transformer is connected to the high-voltage net¬ work parallel to the measuring transformer that is to be checked. Also this measuring system does not cope with the checking of anything else than the individual measur¬ ing transformers. The normal measuring transformer should be able to handle the high-voltages in the high-voltage network with very great accuracy, which means that it must be made very large and heavy. In order to illustrate its size, it may be mentioned that it has a length of 5 m and weighs 1.5 tonnes. It is also disadvantageous that the checking system is dependent on the high-voltage net¬ work. One more drawback of this checking system is that it is only designed for checking of one voltage transfor¬ mer at a time. Thus, there is no prior-art checking system avail¬ able, by which the total errors of an energy measuring system can be determined. A basic requirement placed on such a checking system is that it must be mobile. Not even this basic requirement can be satisfied by using the prior-art technique. Objects of the Invention One object of the present invention is to provide a mobile checking system, by which the total errors of an energy measuring system can be determined. A further object of the present invention is to provide a checking system which is not dependent on the high-voltage network. Summary of the Invention These and other objects of the invention are achiev- ed by a checking system according to the accompanying claim 1. The high-voltage- and heavy-current-generating means contribute to the mobility of the checking system by mak¬ ing the system independent of the high-voltage network, which permits, among other things, normal-current- and normal-voltage-generating means which are considerably smaller than the above-mentioned prior-art normal trans¬ former which is actually mobile. This is due to the fact that it is not necessary to consider the strict operating requirements that are placed on equipment that is to ope¬ rate in the network. A preferred embodiment of the checking system which has the features stated in claim 2 confers the advantage that currents and voltages in the system can be generated at selectable levels. As a result, the energy measuring system can be tested under various operative conditions that may occur in the network, which is not possible by using prior-art technique. Brief Description of the Drawings Fig. 1 shows in a block diagram a checking system according to an embodiment of the present invention. Fig. 2 shows the system in Fig. 1 in more detail. Detailed Description of the Preferred Embodiment Fig. 1 is a block diagram of a checking system according to a preferred embodiment of the present inven¬ tion. The checking system comprises the units which have the reference numeral 1 and are framed by a dash-dotted line. The checking system 1 is shown connected to an energy measuring system 2. The energy measuring system comprises the units having the reference numeral 2 and being framed by a dash-dotted line. The checking system comprises a power supply unit 3, a current combining means 6, a voltage combining means 7, a comparator unit or normal comparator 8, and a control¬ ling and regulating unit 9. The energy measuring system 2 comprises a current detecting unit 21, a voltage detect- ing unit 22 and an energy measuring unit 23. The current detecting and voltage detecting units 21, 22 are con¬ nected to a high-voltage network, from which they can be separated by means of a separator 24. A plant, such as a distribution plant, is, at 26, connected to the end of the lines 25 of the high-voltage network. According to the invention, the checking system 1 is mobile and is preferably arranged in a vehicle, such as a bus, with a trailer. It will be explained in more detail below how this mobility is achieved. The checking system 1 is sup- plied via some external supply other than the high-vol¬ tage network, such as a portable power plant or an AC distribution box. This external supply is connected at 10. The power supply unit 3 is connected to the current combining means 6, which in turn is connected to the nor- mal comparator 8 and an outlet 11. The current detecting unit 21 of the energy measuring system 2 is connected to the outlet 11. The power supply unit 3 is further connected to the voltage combining means 7, which in turn is connect- ed to the normal comparator 8 and an outlet 12. The vol¬ tage detecting unit 22 of the energy measuring system 2 is connected to the outlet 12. The checking system 1 has one more interface towards the energy measuring system, viz. between the normal com- parator 8 and the energy measuring unit 23. The energy measuring unit 23 has an optical outlet 27 and/or a con¬ tact outlet 28. This/these emits/emit pulses at a fre- quency which is proportional to the energy consumption measured by the energy measuring unit 23. The outlet/out¬ lets 27 and/or 28 of the energy measuring unit 23 thus is/are connected to the normal comparator 8. The control- ling and regulating unit 9 is connected to the normal comparator 8 for collecting measured values from this, and to the power supply unit 3 for determining the fre¬ quency of the current and the voltage leaving the power supply unit. The controlling and regulating unit thus regulates the current and the voltage leaving the power supply unit 3, the feedback consisting of the measured values from the normal comparator. In the embodiment illustrated, the checking system 1 operates in 3-phase (three currents and three voltages). This should be seen as an example only. Other system variants, e.g. three currents and two voltages are, of course, possible within the scope of the invention. The checking system 1 briefly functions as follows. The power supply unit 3 generates current in three phases and supplies this to the current combining means 6. The current combining means 6 generates heavy current (in three phases) , of the same magnitude as the current in the high-voltage network, at very low voltage and sup¬ plies this heavy current to the current detecting unit 21. The current combining means 6 also generates a refe¬ rence or normal current and supplies this to the normal comparator 8. The current is stepped down in the current detecting unit 21 and supplied to the energy measuring unit 23. The power supply unit 3 also generates voltage in three phases and supplies this voltage to the voltage combining means 7. The voltage combining means 7 gene¬ rates high voltage (in three phases) of the same magni¬ tude as the voltage in the high-voltage network, at very low current, and supplies this high voltage to the vol¬ tage detecting unit 22. The voltage combining means 7 also generates a reference or normal voltage and supplies this to the normal comparator 8. The voltage detecting unit 22 steps the voltage down and supplies the stepped- down voltage to the energy measuring unit 23. The energy measuring unit 23 measures the power flow. The normal comparator 8 determines a reference or normal power flow and compares this with the correspond¬ ing value collected from the optical outlet 27 of the energy measuring unit 23. The difference then detected by the normal comparator is a measure of the total error of measurement in the energy measuring system 2. The controlling and regulating unit 9, which here is a PC, is used to control and regulate the checking system, which comprises the step of controlling, via the power supply unit 3, the phase relation, frequency and amplitude of the currents and voltages. The checking system 1 according to the invention will now be described in more detail with reference to Fig. 2. The power supply unit 3 comprises a current gene¬ rator 4, a voltage generator 5, a power pack 41, which is connected to the external power source and to the current and voltage generators and which supplies direct voltages to each generator 4, 5, and a first 42 and second 43 function generator which generates and supplies to the current generator 4 and the voltage generator 5, respec- tively, signals for controlling frequency and amplitude of the currents and voltages generated by the generators 4, 5 and for controlling the mutual phases between the currents and between the voltages. The current combining means 6 has three inlets, one for each phase. To each inlet are connected two conduc¬ tors 44, 45; 46, 47; 48, 49 from the generator 4. The conductors 44, 45; 46, 47; 48, 49 are connected to the primary side of transformers 50-52 for stepping up the currents supplied from the current generator 4. The secondary side of each transformer 50-52 has two connec¬ tions 53, 54; 55, 56; 57, 58 which are connected to the primary side of a measuring transformer 59, 60, 61 in the current detecting unit 21. Between one connection 54, 56, 58 of each transformer and the measuring transformer 59-61, a normal transformer 62, 63, 64 is connected. Consequently, the same current flows through the normal transformer 62-64 and the measuring transformer 59-61. Each measuring transformer 59-61 steps down the current and supplies it to the energy meter or Wh meter 23, to which the secondary side of the measuring transformer 59, 60, 61 is connected. The normal transformers 62-64 step down the currents by essentially the same transformation factor and then supply them to a normal meter 65 in the comparator unit 8. The current transformers 50-52 for stepping up are designed in such manner that they generate in their secondary windings great currents, for instance 600 A or 1200 A, while the voltage drop across the secondary wind¬ ings is extremely low, a few volts. This results in the power development in the transformers 50-52 being very low and thus the possibility of making the transformers 50-52 relatively small. This is necessary for the mobi¬ lity and the requirement that the connection cables for the great currents be short (about a meter) . The voltage combining means 7 comprises three trans¬ formers 66-68 for stepping up the voltages supplied by the voltage generator to high-voltage levels, such as 20 kV or 130 kV, and three normal transformers 69-71. Each of the transformers 66-68 is connected to a measur¬ ing transformer 72-74 for voltage detection. Each measur¬ ing transformer 72-74 steps down the voltage and supplies it to the energy meter 23. Each normal transformer 69, 70 or 71 is connected to the secondary side of one of the transformers 66, 67 or 68 and steps down the voltage by essentially the same transformation factor as the measur¬ ing transformers so as then to supply the voltage to the normal meter 65. The transformers 66-68 are designed such that they generate the high voltage at low current, for instance some twenty or thirty milliamperes. They are of a relatively seen small size, which is possible owing to the low power they need to cope with and owing to the fact that they need not be designed in the same manner as the operating transformers. In the normal meter, a value is determined, which in the following is called normal value, of the inlet ener¬ gy. The normal value is supplied to a comparator circuit 75 in the comparator unit 8. The energy meter 23 deter¬ mines a corresponding value, below called measured value, that applies to the energy measuring system 2. The mea¬ sured value is supplied to the comparator circuit 75 via the optical outlet 27 and is there compared with the nor¬ mal value. The difference constitutes the total error of measurement in the entire energy measuring system 2. This total error cannot be determined by conventional measur¬ ing methods. As indicated by dashed lines, the system 1 may also be used for checking each of the measuring transformers 59-61, 72-74, the comparator unit 8 having inlets arrang- ed for the purpose. The inventive checking system is mobile. More spe¬ cifically, it is arranged in a vehicle, preferably a bus with a trailer. The high-voltage transformers are arrang¬ ed on the trailer, and the rest of the system 1 is ar- ranged in the bus, which means that only short cables between the trailer and the bus are required for trans¬ mitting the low voltages and currents. Furthermore, the distances between the transformers 50-52; 66-68 and the normal transformers 62-64; 69-71 are short. The new ways of thinking according to the invention and the unique design of the system as described above have yielded com¬ ponents of such a small size that the entire system can be accommodated in a bus with trailer. Consequently the entire system will be extremely mobile. This results in great cost savings since no mounting and dismounting of components in the energy measuring system takes place. An advantage of the inventive checking is that it involves an immediate comparison and is not based on the necessity of determining an absolute value. It is there¬ fore not critical if the currents and voltages supplied to the measuring transformers 59-61; 72-74 vary somewhat in time since the variations are reflected both in the energy measuring system 2 and in the checking system 1. A further important advantage is that the stepping-up transformers included in the checking system need not be of the same size in terms of power as the stepping-up transformers used in prior art when checking individual measuring transformers in the laboratory, which means that they can be made considerably smaller. Finally, it is an advantage that the checking sys- tern 1 does not require access to the high-voltage net¬ work, but is supplied by another source, preferably a fuel-powered, portable power plant. Consequently, the load ratio on the network is not interfered with by the checking and vice versa. Moreover, a difficult connection to the high-voltage network is avoided (short-circuit effects etc. ). Further the normal transformers operate under controlled conditions in each measurement, which means that one is well acquainted with the any ratio er¬ rors of the normal transformers and other values that vary with the supplied current/voltage and the environ¬ ment. The connection to another power source than the high-voltage network also confers the advantage that the dimensions of the normal transformers can be sig- nificantly reduced in relation to the above-mentioned prior-art mobile normal transformer. The reason for this is that the requirements for insulation properties as well as other properties to make the transformer cope with the operation conditions and the safety in the high- voltage network do not exist. The PC is an important utensil to make the measure¬ ment rational and to rapidly perform any correction cal¬ culations and account for the measurement result.

Claims: CLAIMS 1. A checking system for control measurement of an energy measuring system which is connected in a high- voltage network and which is used to measure the energy consumed in a plant, e.g. a distribution plant, connected to the high-voltage network, and comprises an energy mea¬ suring unit (23), a current detecting unit (21) connected to the energy measuring unit and adapted to detect the current consumed, and a voltage detecting unit (22) con¬ nected to the energy measuring unit and adapted to detect the corresponding voltage, c h a r a c t e r i s e d in that the checking system (1) is mobile, and that the checking system comprises a high-voltage-generating means (66-68) to be connected to the voltage detecting unit of the energy measuring system, a heavy-current-generating means (50-52) to be connected to the current detecting unit of the energy measuring system, a normal-current- generating means (62-64) connected to the heavy-current- generating means and adapted to generate a normal cur¬ rent, a normal-voltage-generating means (69-71) connected to the high-voltage generating means and adapted to generate a normal voltage, and a comparator unit (8), which is connected to the normal-current-generating means for receiving the normal current and to the normal- voltage-generating means for receiving the normal voltage and which is adapted to be connected to the energy measuring unit for receiving a measured value, determined by the energy measuring unit, of the consumed energy, the comparator unit being adapted to determine a normal value of the consumed energy and to compare the normal value with the measured value and determine the difference therebetween, said difference being a measure of the total error of measurement of the energy measuring system. 2. The checking system as claimed in claim 1, c h a r a c t e r i s e d in that it comprises a power supply unit (3) which is connected to an external power source and which is adapted to generate currents and vol- tages, respectively, to the heavy-current-generating means and the high-voltage generating means, respective¬ ly, said currents and voltages having a predetermined frequency, amplitude and phase. 3. The checking system as claimed in claim 2, c h a r a c t e r i s e d in that it comprises a control¬ ling and regulating unit (9), which is connected to the power supply unit for regulating said frequency, ampli¬ tude and phase. 4. The checking system as claimed in claim 2 or 3, c h a r a c t e r i s e d in that the power supply unit comprises a current generator (4), which is connected to the heavy-current-generating means, a voltage generator ( 5), which is connected to the high-voltage generating means, a first function generator (42), which is connect- ed to the current generator, and a second function gene¬ rator (43), which is connected to the voltage generator. 5. The checking system as claimed in any one of the preceding claims, the current detecting unit of the ener¬ gy measuring system comprising at least one current mea- suring transformer and its voltage detecting unit com¬ prising at least one voltage measuring transformer, c h a r a c t e r i s e d in that the high-voltage gene¬ rating means comprises at least one voltage transformer (66-68), which generates the high voltage at extremely low current, whose amplitude is below 0.1 A, that the heavy-current-generating means comprises at least one current transformer which generates the heavy current at extremely low voltage, whose amplitude is below 10 V, that the normal-voltage-generating means comprises at least one voltage normal transformer, and that the nor¬ mal-current-generating means comprises at least one cur¬ rent normal transformer, the voltage transformer being connected to the voltage normal transformer and adapted to be connected to the voltage measuring transformer to make this connected in parallel with the voltage normal transformer, and the current transformer being connected to the current normal transformer and adapted to be con¬ nected to the current measuring transformer to make this connected in series with the current normal transformer. 6. The checking system as claimed in any one of the preceding claims, c h a r a c t e r i s e d in that the comparator unit is adapted to be connected to at least one current and/or voltage measuring transformer.

Inventors: JOENSSON KJELL, JOENSSON, KJELL
Applicants: JOENSSON KJELL, SYDKRAFT AB, JOENSSON, KJELL
Application year: 1996
Main classification: G01D21
IPC codes: G01R35