RU2096789C1 - Device which measures characteristics of electric power supply line - Google Patents

Abstract

FIELD: electric instruments, in particular, electric power supply line registers. SUBSTANCE: device has first and second access units which have inputs respectively for connection to transducers of phase current and phase voltage in line. In addition device has analog-to-digital converter, processing unit and communication line from output of analog-to- digital converter to input of processing unit. Output of input current transducer in first access unit and output of transducer of input voltage from second access unit are connected to first and second inputs of analog-to-digital converter respectively. Input voltage transducer is introduced to first access unit, input current transducer is introduced to second access unit, third and fourth inputs are introduced to analog-to-digital converter, processing unit takes into account errors of transducers to accomplish the goal of invention. Third input of analog-to-digital converter is connected to output of input voltage transducer from first access unit. Fourth input of analog-to-digital converter is connected to output of input current transducer of second access unit. This results in possibility to correct input data of device depending on real error which is caused by current and voltage transformers. EFFECT: increased precision of measurement. 2 cl, 3 dwg

Description

 The invention relates to electrical engineering and can be used, for example, in the construction of energy meters of the power grid.

 The best electromechanical network energy meters have a measurement accuracy limited to 0.5.

 The development of electronic analog and then digital electricity meters has opened up new possibilities in increasing the measurement accuracy by about an order of magnitude.

 The improvement of electronic electricity meters of the network, which continues to this day, goes in the direction of compensating for hardware errors or errors that occur in special modes of operation of the electric network.

 It is known, for example, an electronic device for measuring electrical energy [1] in which, to increase the accuracy of the measurement, the sampling of voltages and currents in all phases is tightly synchronized with the voltage period of the first phase.

 Known digital meter of electrical energy [2] in which the compensation of non-linear components of the errors that occur when measuring the energy of the grid with rapidly changing loads.

 Known taken as a prototype electronic meter of power and energy [3] in which to improve the accuracy of the conversion of bipolar input signals to unipolar. The prototype device [3] contains two sampling units, a signal conversion unit, a communication line, a control and processing unit.

 A common drawback of the known solutions, including the prototype [3], is their inability to take into account the real error introduced by the measuring transformers (transformers) of the current and voltage of the power supply network (CT and VT), from the secondary circuits of which the input signals for the electronic meter are removed. The indicated error, as shown by studies of CTs and VTs in operation, can significantly differ from those recorded in the passport, and depends on the electrical mode of operation of the CTs and VTs, as well as on the ambient temperature. The real deviations of the errors of the CTs and VTs in operation from those recorded in the passport are so significant that their neglect negates the advantages of the accuracy of the electronic measuring system over the electromechanical.

 The objective of the invention is to create a meter that takes into account changes in the error of current and voltage transformers during their operation and, thus, is able to actually provide increased accuracy of measuring the parameters of the power supply mode.

 The subject of the invention is a power network mode meter, comprising at least two sampling units, an analog-to-digital conversion unit, a processing unit and a communication line of the output of the analog-to-digital conversion unit with an input of the processing unit, the group of outputs of which form the information outputs of the meter, the data input the first sampling unit is designed to connect to the measuring transformer of the phase current of the mains, the data input of the second sampling unit is designed to connect to measure To the first phase sample voltage converter, the input current sensor output of the first sample unit and the input voltage sensor output of the second sample unit are connected to the first and second inputs of the analog-to-digital conversion unit, respectively, different according to the invention, in that an input current sensor is introduced into the first sample unit, and the analog-to-digital conversion unit is equipped with third and fourth inputs, to which the outputs of the input voltage sensor of the first sampling unit and the input current sensor of the second are connected sampling unit, respectively, the processing unit is configured to calculate the errors of the transducers and take them into account when determining the parameters of the power supply mode.

 A device characterized by the indicated combination of features takes into account changes in the error of current and voltage measuring transducers in operation, depending on the electric mode of the network and, thus, can really ensure a measurement accuracy corresponding to class 0.1.

 The invention has a development in that the processing unit is provided with an additional input for connecting to an ambient temperature sensor. This allows you to take into account temperature changes in the error of the measuring transducers and to further increase the measurement accuracy.

The invention is illustrated by drawings.
In FIG. 1 shows a block diagram of a meter with the disclosure of the implementation of the sample blocks in relation to one phase of the mains; in FIG. 2 diagram of the internal implementation of the conversion unit; in FIG. 3 is a functional diagram corresponding to the algorithm of the processing unit.

 The device of FIG. 1 contains the first and second blocks 1 and 2 of the sample, block 3 of the analog-to-digital signal conversion, communication line 4 of the output of block 3 with the input of processing block 5, the group of outputs 6 of which forms the information outputs of the meter.

 Block 1 has an input 7 of data and outputs 8.9, and block 2 an input 10 of data and output 11, 12. Output 8 is the output of the sensor 13 of the input current of block 1 and is connected to the first input 14 of block 3, and the output 11 is the output of the sensor 15 the input voltage of block 2 and is connected to the second input 16 of block 3.

 An input voltage sensor 17 is introduced into the unit, and an input current sensor 18 is introduced into the unit 2. In this case, the unit 3 is equipped with a third input 19, to which the output 9, which is the output of the sensor 17, is connected, and a fourth input 20, to which the output 12, which is the output of the sensor 18, is connected.

 Inputs 7 and 10 of blocks 1 and 2 are designed to connect to the measuring transducers 21 and 22, respectively, of the phase current and phase voltage of the mains.

 The processing unit 5 may be provided with an input 23 for connecting to an ambient temperature sensor 24.

 Measuring transducers 21 and 22 (transformers of phase current and phase voltage, respectively), as well as sensor 24 (see the dotted line in FIG. 1) are not included in the claimed object and are shown in FIG. 1 to explain the operation of the device.

 Block 3 in relation to one phase of the power supply can be made in the form (Fig. 2) of analog-to-digital converters 25, 26, 27, 28 at the inputs and a multi-channel switch 29 at the output.

 As line 4, a wired or fiber-optic communication line can be used with the output of the serial to parallel converter.

 Block 5 can be performed on the basis of a microcomputer that performs calculations in accordance with the functional diagram of figure 3.

 The meter works as follows.

 The inputs 7 and 10 receive the instantaneous values of the signals from the secondary circuits of the current transformer 21 and voltage transformer 22 of the mains phase voltage.

 With the output 8 and 9 of block 1, the instantaneous values of the current and voltage of the phase current transformer 21 are taken, and from the outputs 11 and 12 of block 2 are the instantaneous values of the voltage and current of the phase voltage transformer 22.

 The indicated signals are converted in block 3 into a serial digital code and, having passed the communication line 4, are sent to block 5 for processing.

Block 5, according to the functional diagram of FIG. 3, according to the instantaneous values of the current i _I and voltage u _{I of the} secondary circuit of the current transformer 21, as well as the current i _U and voltage u _{U of the} secondary circuit of the voltage transformer 22, it calculates the rms values I _I , D _I , I _U , U _U for the period T AC mains.

In addition, block 5 determines the angle Φ between the current i _{I of the} current transformer 21 and the voltage u _{U of the} voltage transformer 22, the active power P, the apparent power S and the reactive power Q.

The values I _I , U _I , I _I , U _u , v and additionally temperature (input 23) are the initial data for calculating the amplitude (ΔI and ΔU) and angular (ΔΦ _I and ΔΦ _U ) errors of current and voltage transformers 21 and 22. The calculated errors ΔI, ΔU, ΔΦ _I , ΔΦ _U are used in block 5 to determine (see Fig. 3) the refined (index "y" in Fig. 3) the values of current I _y , voltage U _y , active power P _y , seeming power S _y and reactive power Q _y .

Electricity A _{y is} calculated by continuously summing the products P _y T.

 Thus, the proposed solution allows you to select and use as initial data for the calculation of the desired parameters not only the instantaneous current values of current transformers (CT) and instantaneous voltage values of voltage transformers (VT), but also the instantaneous voltage values of CTs, as well as instantaneous current values of VTs and additionally the temperature of the medium.

 That is, in the claimed device, the initial calculations are data that continuously monitors changes in the operating points of the volt ampere characteristics of the current transformers and current transformers, and additionally the temperature that affects the position of these operating points.

 Therefore, the claimed solution allows the correction of the measurement output parameters depending on the actual error introduced by the current and voltage transformers in operation, and, accordingly, to improve the accuracy of the measuring system as a whole.

 According to the circuit of FIG. 1, taking into account the implementation of block 3 according to the scheme of FIG. 2 and execution according to the algorithm corresponding to FIG. 3, a layout of the proposed device was assembled. In this case, block 3 was performed using the integrated circuit K1108PV2 and provided a conversion time and write to the memory of the calculator 5, equal to 3 μs per channel. The sampling frequency of the analog-to-digital conversion was 50 kHz. calculations according to the algorithm corresponding to the functional diagram of FIG. 3, were carried out on an IBM PC AT computer after inputting initial data for 10 periods of mains voltage.

 Comparative tests provided for measurements of the same energy parameter of the mains when the load changed from 0.8 to 1.0, using first current transformers and voltage of accuracy class 0.2, and then another accuracy class of 0.5.

 The measurement results, as expected, did not match. However, when performing measurements using an exemplary counter type CE6802, changes in the result, i.e., measurement errors, amounted to 0.58, and when using the layout assembled in accordance with the invention, only 0.17

Claims (2)

 1. The meter mode parameters of the electric network, containing at least the first and second sampling units with sensors of the output current and input voltage, respectively, the analog-to-digital conversion unit, the processing unit and the communication line of the output of the analog-to-digital conversion unit with the input of the processing unit, group of outputs which forms the information outputs of the meter, and the data input of the first sampling unit is designed to be connected to the measuring transformer of the phase current of the mains, the data input of the second The gate is designed to be connected to the measuring transducer of the mains phase voltage, the input current sensor output of the first sampling unit and the input voltage sensor output of the second sampling unit are connected to the first and second inputs of the analog-to-digital conversion unit, respectively, characterized in that an input sensor is introduced into the first sampling unit voltage, an input current sensor is introduced into the second sampling unit, and the analog-to-digital conversion unit is equipped with third and fourth inputs, to which the outputs are connected the input voltage sensor of the first sampling unit and the input current sensor of the second sampling unit, respectively, while the processing unit is configured to calculate the errors of the measuring transducers of the phase current and phase voltage and take these errors into account to determine the updated values of the parameters of the power supply mode, received at the group of information outputs of the meter.  2. The meter according to claim 1, characterized in that the processing unit is equipped with an additional input for connecting to an ambient temperature sensor.

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