CN201438211U - An electronic transformer calibration device - Google Patents

Abstract

The utility model relates to an electronic transformer calibration device, which comprises a standard transformer, an isolation circuit, an integrated operational amplifier circuit, an analog/digital converter, a photoelectric conversion module, a synchronous data acquisition circuit for collecting signals, and a circuit for processing A computer for collecting signals; the standard transformer is connected to an isolation circuit; the isolation circuit is sequentially connected to a synchronous data acquisition circuit through an integrated operational amplifier circuit and an analog/digital converter; the photoelectric conversion module is connected to a synchronous data acquisition circuit; The synchronous data acquisition circuit is connected to a computer. The device can calculate the frequency, ratio difference and angle difference in real time, and display parameters such as waveform and effective value, realize storage, summary and other functions, and can obtain more accurate and stable measurement values, and the calculation speed can fully meet the needs , and the device has the characteristics of small size, convenient portability and high precision.

Description

An electronic transformer calibration device

technical field

The utility model belongs to the technical field of high-voltage power metering and relay protection devices, in particular to an electronic transformer calibration device.

Background technique

At present, in the field of high-voltage measurement, due to the continuous improvement of grid capacity and voltage level, the electromagnetic and capacitive voltage transformers that have been used in large quantities are getting larger and larger, and the cost is getting higher and higher. Or SF6 gas insulation, with environmental and safety hazards, it is difficult to meet the signal output requirements of modern digital power stations.

In recent years, domestic and foreign manufacturers have invested a lot of manpower and material resources in the research and development of new electronic transformers. Modern electronic transformers cancel the power requirements for signal output, which makes it possible to develop miniaturized and low-power electronic transformers. The new electronic transformer has digital output and is transmitted by optical fiber, so there is no interference, but it brings new problems to the accuracy measurement. First, the standard transformer is an analog output, while the measured transformer is a digital output. If Reverting the digital signal to an analog signal and using the traditional method to calibrate, the accuracy of the digital signal will be greatly lost, which cannot meet the calibration accuracy requirements. Calibration of the electronic transformer is a prerequisite to ensure its successful application in the power system. The utility model digitizes the analog signal, and then uses the mathematical FFT method to calculate, and obtains the error of the standard transformer and the measured transformer. Practice has proved that this method is very effective, greatly reducing the transmission error in the calibration process, and fully meeting the user's calibration requirements for electronic transformers.

Utility model content

The utility model proposes an electronic transformer calibration device aiming at the problems existing in the calibration process of the current electronic transformer.

An electronic transformer calibration device, which is special in that the device includes a standard transformer, an isolation circuit, an integrated operational amplifier circuit, an analog/digital converter, a photoelectric conversion module, and a synchronous data acquisition circuit for collecting signals and a computer for processing the acquisition signal; the standard transformer is connected to the isolation circuit; the isolation circuit is sequentially connected to the synchronous data acquisition circuit through the integrated operational amplifier circuit and the analog/digital converter; the photoelectric conversion module is connected to the synchronous A data acquisition circuit; the synchronous data acquisition circuit is connected to a computer.

The above-mentioned synchronous data acquisition circuit is a programmable controller CPLD.

The above-mentioned standard transformer is a standard current transformer or a standard voltage transformer, and the isolation circuit is a zero-flux current transformer or a zero-flux voltage transformer.

The utility model can calculate the frequency, ratio difference and angle difference in real time, and display parameters such as waveforms and effective values, realize functions such as storage and summarization, and can obtain more accurate and stable measurement values, and the calculation speed can fully The requirement is met, and the device has the characteristics of small volume, convenient portability and high precision.

Description of drawings

Fig. 1 is a block diagram of the utility model;

Fig. 2 is the circuit schematic diagram of the present utility model;

Fig. 3 is the schematic diagram of the circuit when checking the electronic current transformer;

Fig. 4 is a schematic diagram of the circuit when calibrating the electronic voltage transformer.

Detailed ways

Referring to Figures 1 and 2, the electronic transformer calibration device described in the utility model includes a standard transformer, an isolation circuit, an integrated operational amplifier circuit, an analog/digital converter, a photoelectric conversion module, and synchronous data for collecting signals. acquisition circuit and a computer for processing the acquisition signal; the standard transformer is connected to the isolation circuit; the isolation circuit is connected to the synchronous data acquisition circuit through the integrated operational amplifier circuit and the analog/digital converter; the photoelectric conversion module is connected to the into a synchronous data acquisition circuit; the synchronous data acquisition circuit is connected to a computer.

Wherein, the standard transformer is a standard current transformer or a standard voltage transformer, and the isolation circuit is a zero-flux current transformer or a zero-flux voltage transformer; the electronic transformer calibration device also includes a To provide a signal generator for input signals, the signal generator is connected to a standard transformer; the signal generator is a current generator or a voltage generator; the synchronous data acquisition circuit uses the EPM1270 CPLD of ALTERA Company.

The standard transformer generates an output signal under the excitation of a signal generator (current generator or voltage generator). The output signal is an analog signal. The analog signal is sampled by an integrated operational amplifier to obtain a sampling signal; then the sampling signal is passed through The analog/digital conversion (A/D) chip is converted into a digital signal; and the digital signal is sent to the synchronous data acquisition circuit, and the synchronous data acquisition circuit synchronously samples the digital signal and the digital signal output by the electronic transformer under test , and then obtain the sampling signal, and finally transmit the sampling signal to the host computer through the USB module circuit and perform FFT calculation on the sampling signal to obtain the ratio difference (difference in amplitude between the measured transformer and the standard transformer when measuring the signal) and The calculation result of the angle difference (the phase difference between the measured transformer and the standard transformer when measuring the signal); generally, it is necessary to obtain multiple such calculation results, and take the average value of these multiple calculation results as the final calculation result (measurement result ), that is, it is necessary to repeat steps 1 to 5 multiple times, and generally repeat steps 1 to 5 at least three times.

The analog/digital conversion (A/D) chip adopts a 16-bit analog/digital conversion (A/D) chip with a maximum sampling frequency of 500KHZ.

Among them, the digital signal output by the electronic transformer under test is an optical signal, so it is necessary to convert the optical digital signal into an electrical signal through a photoelectric conversion module (circuit), and then send it to the synchronous data acquisition circuit; moreover, in order to prevent the standard mutual inductance The impact of the transformer on the electronic transformer under test, the analog output of the standard transformer is isolated through the isolation circuit, and the selection of the rated value of the transformer with zero magnetic flux shall not affect the electronic transformer under test. .

The synchronous data acquisition circuit here is a programmable controller CPLD.

Under asynchronous sampling, traditional FFT has leakage effect and fence effect, which makes the calculated frequency, amplitude and phase errors larger. In order to reduce the influence of asynchronous sampling on FFT and improve the calibration accuracy, we use the improved high-precision FFT algorithm.

According to the knowledge of digital information processing, the interpolation algorithm can eliminate the error caused by the fence effect, and the window processing can reduce the leakage effect. In order to improve the precision of FFT, the utility model adopts the interpolation algorithm based on Blackman2Harris window; the range of fundamental frequency variation of grid voltage is generally 49.15Hz-50.15Hz.

The windowing function in the algorithm of the present utility model is:

cyc=4n

Num=4k*cyc

pi=3.1415926536

For i＝0 To Num

win(i)＝0.35875-0.48829*Cos(2*pi*i/Num)+0.14128*Cos(4*pi*i/Num)-0.01168*Cos(6*pi*i/Num)

Next I

Wherein, cyc is the number of sampling cycles for each calculation, and the Num is the total sampling points for each calculation; the n≥1, k≥1, and both n and k are natural numbers.

N=2 in this implementation example, k=24, namely each measurement in the utility model, sampling 8 cycles (period) signal, 96 points per cycle (sampling 96 times in each period) (sampling frequency is 4.8KHZ) , so N(Num)=96*8=768, (actually need to collect more, remove the beginning and end in the program).

In order to further reduce the error caused by the random fluctuation of the grid voltage and obtain more stable measurement results, the system automatically and continuously samples and calculates 10 times (about 8 cycles each time) during each measurement, and takes the average value of the 10 calculation results as final result. Practice has proved that this method can obtain more accurate and stable measurement values, and the calculation speed can fully meet the needs.

Referring to Figures 3 and 4, the measurement accuracy of the standard transformer in the utility model is two grades higher than that of the electronic transformer to be tested. The measurement accuracy of the standard transformer is generally 0.1 or 0.01, and the standard Transformer refers to standard current transformer CT 1 or standard voltage transformer PT 2, and the electronic transformer to be tested is electronic current transformer CT 3 or electronic voltage transformer PT 4 with optical fiber digital output.

The rated output current of the standard current transformer here is 5A; the rated output voltage of the standard voltage transformer is 100V/√3V; at the same time, the rated output value of the corresponding current generator 5 or voltage generator 6 should meet the standard current mutual inductance The input current or input voltage requirements of transformer 1 or standard voltage transformer 2.

And in the utility model, the requirement for the current generator 5 or the voltage generator 6 is mainly to meet the requirements of the measured electronic current transformer CT 3 or the electronic voltage transformer PT 4, such as the rated current transformer CT 3 The current is 600A, then the maximum output of the current generator 5 must be greater than 600A.

The utility model adopts AC 220V±5% power supply for power supply.

Rated input to be calibrated: digital (optical fiber or wire) CT/metering: 2D41H (11585); CT/protection: 1CFH (463); PT/metering protection: 2D41H (11585); standard transformer input analog: CT: 5A ; PT: 100/√3V; Calibration accuracy level 3.0; Sampling accuracy is 16 bits, 80-500 points/cycle, using IEC-60044-8 standard communication protocol.

Claims (3)

1. checking electronic type transformers device is characterized in that: this device comprises standard mutual inductor, buffer circuit, integrated operational amplifier circuit, A/D converter, photoelectric conversion module, in order to the synchronous data collection circuit of acquired signal with in order to handle the computing machine of acquired signal; Described standard mutual inductor inserts buffer circuit; Described buffer circuit inserts the synchronous data collection circuit by integrated operational amplifier circuit, A/D converter successively; Described photoelectric conversion module inserts the synchronous data collection circuit; Described synchronous data collection circuit inserts computing machine.

2. checking electronic type transformers device according to claim 1 is characterized in that: described synchronous data collection circuit is Programmable Logic Controller CPLD.

3. checking electronic type transformers device according to claim 1 and 2 is characterized in that: described standard mutual inductor is standard current transformer or standard potential transformer, and described buffer circuit is the current transformer of zero magnetic flux or the voltage transformer (VT) of zero magnetic flux.

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