CN205594091U - Error measurement device for current transformer - Google Patents

Abstract

The utility model provides a current transformer error measuring device, which comprises a power generator (1), a reference standard device (2) and an error tester (3), and the power generator (1) generates a large current AC/DC composite signal or half-sine-wave signal, and the generated signal is respectively applied to the measured current transformer (4) and the reference standard (2); The composition is accurately converted into a small current or small voltage signal, and the small current or small voltage signal is input to the error tester (3) as a reference signal; the error tester (3) compares the reference signal output by the reference standard (2) with the measured The measured signal output by the current transformer (4) is synchronously sampled, converted and calculated to obtain a measurement result.

Description

A current transformer error measuring device

technical field

The utility model relates to the field of electrical measurement, in particular to a current transformer error measuring device.

Background technique

Current transformer is the key equipment for electric power production, electric energy measurement and protection. In the process of power production, a large number of current transformers are used in power generation, power transformation and other links to measure and protect high-voltage and high-current electric energy. If there is a DC component in the primary current in the power grid, the iron core of the current transformer in the electric energy metering device will be magnetized, and the greater the magnetizing current, the greater the residual magnetism. In the case of no demagnetization, the residual magnetism can be kept until the next magnetization process. The influence of residual magnetism on the error of current transformer can be reflected in the magnetization curve of magnetization current. For standard silicon steel sheets and iron-nickel alloy samples, weak remanence mostly causes the transformer error to change in the positive direction, and strong remanence will inevitably cause the transformer error to change in the negative direction.

Due to the following reasons, the power grid produces a DC component: (1) The geomagnetic current caused by the solar storm. The change of the earth's magnetic field will induce a potential gradient on the earth's surface. In areas with low ground conductivity, when a low-frequency electric field that lasts for a period of time acts on a power transformer whose neutral point is grounded in the transmission system, the potential gradient on the earth's surface will be induced at the frequency of its winding. Compared with the 50Hz AC system, the geomagnetic induction current (GIC) of 0.0001Hz～0.01Hz can be regarded as an approximate DC. (2) Underground direct current generated by the operation of the single pole ground circuit of DC power transmission. my country has put into operation a number of 500kV, 800kV HVDC transmission lines. In the single-stage earth loop operation mode or the bipolar unbalanced operation mode, the current flowing through the earth as the DC transmission circuit is the operating current of the DC transmission system, and the ground surface potential will be generated in a certain area around the converter station, making the surrounding neutral A point-grounded transformer produces a DC component at the neutral point. (3) DC component generated by unsymmetrical load. There are loads with asymmetrical voltage-current relationship curves in the AC network. For example, phase-controlled AC loads, phase-controlled rectifiers, single-wave rectifiers, and line-commutated inverters all generate DC components. In addition, in DC transmission systems with controlled asymmetry and in some frequency converter systems, transformer windings contain DC components.

Generally, the transformer calibrator is used to measure the error of the current transformer. The general transformer calibrator adopts the principle of differential balance comparison. The advantage of this kind of calibrator is its high accuracy, and its resolution can reach 1×10-8. It can be used to calibrate transformers of 0.0001 level and below. The disadvantage is that this kind of calibrator needs manual adjustment, it is difficult to check zero balance, and it is inconvenient to use. Another commonly used transformer calibrator adopts microcomputer technology and unbalanced differential principle to measure the differential signal of the secondary circuit of the transformer and the secondary circuit of the standard transformer and the working signal of the secondary circuit of the standard transformer, and according to the error Define the formula to calculate the error of the transformer. Although the working efficiency of the latter is higher than that of the traditional electrical calibrator, the circuit is complex and difficult to debug. When the differential signal is small, the measurement accuracy and stability are not good, and the repeatability is poor, and it is generally only suitable for testing 0.01 Transformers below the level.

The existing transformer calibrator can only be calibrated and traced at 50/60Hz. Due to the limitations of its components and working principle, none of them can work under the conditions of high harmonics or high DC components, and cannot be used to measure current transformers. The error characteristics when DC and harmonics are affected, so it is necessary to provide a new type of measurement device and measurement method.

Utility model content

Aiming at the deficiencies of the prior art, the utility model proposes a current transformer error measurement device, which uses data acquisition technology and digital signal processing technology to directly measure the secondary signal of the current transformer, and calculates its effective value error and fundamental wave amplitude error , Fundamental wave phase error, as the evaluation basis for evaluating the harmonic and anti-DC performance of the current transformer.

A current transformer error measurement device, comprising a power generator (1), a reference standard (2) and an error tester (3); the power generator (1) is connected to the reference standard (2) and the measured Transformer (4) is connected, and described error tester (3) is connected with reference standard device (2), and is provided with the connecting end that is connected with tested transformer (4), and described reference standard device (2) is provided with The connection end connected with the measured transformer (4), the measuring device adopts two modes of AC and DC composite signal or half-sine wave signal.

When the device adopts the AC-DC synthesis signal mode, the power generator (1) includes an AC current source (5) and a DC current source (6), and the AC current source (5) includes a voltage regulator and a current booster , one end of the current booster is connected to the capacitor C, the other end of the capacitor C is connected to the inductor L, the other end of the inductor L is connected to one end of the DC current source (6), and the other end of the current booster is connected to the The other end of the direct current source (6) is connected.

When the device adopts the half-sine wave signal mode, the power generator (1) includes an AC current source (5) and a rectifier diode, the AC current source (5) includes a voltage regulator and a current booster, and the booster One end of the current booster is connected to the resistor R, the other end of the resistor R is respectively connected to the anode of the first diode and the cathode of the second diode, and the other end of the current booster is connected to one end of the resistor _RB , so The other end of the resistor _RB is connected to the anode of the second diode.

The reference standard (2) adopts AC and DC universal measuring equipment such as precision shunts and zero-flux sensors, and its DC and AC amplitude errors are less than 0.05%, and the power frequency AC phase error is less than 2 minutes.

The error tester (3) includes a sampling resistor, a dual-channel data acquisition card and a data processing module.

The rated current of the sampling resistor is 1A or 5A, the error is less than 0.01%, and the current signal is converted into a voltage signal.

The resolution of the dual-channel data acquisition card is not lower than 24bit, and the reference signal and the signal under test are sampled synchronously.

Compared with the closest prior art, the technical solution provided by the utility model has the following excellent effects

(1) The DC content in the primary large current loop can be adjusted arbitrarily, and AC half-wave can be generated, which can simulate a variety of different on-site operating conditions;

(2) Using a shunt or a zero-flux sensor that can simultaneously measure AC and DC signals as a reference standard can accurately monitor the DC content in the primary current and improve the consistency of test results;

(3) The error tester adopts digital direct measurement technology, which overcomes the shortcomings of the traditional calibrator that cannot work under the influence of harmonics and DC, and requires the same transformation ratio of the standard device and the measured transformer, and can test the effective value as needed , amplitude, and phase other parameters, while its high degree of automation improves measurement efficiency.

Description of drawings

Fig. 1 is a structural block diagram of a current transformer DC and harmonic influence measuring device of the present invention;

Fig. 2 is the schematic diagram when the power supply generator in the utility model produces the AC-DC synthesis signal;

Fig. 3 is a principle diagram when the power generator in the utility model generates a sine half-wave signal.

detailed description

Below in conjunction with accompanying drawing and specific embodiment, the utility model is described in further detail.

As shown in accompanying drawing 1, it is the structural block diagram of a kind of current transformer DC and harmonic influence measuring device of the present invention, is made up of power generator 1, reference standard device 2 and error tester 3, described power generator 1 They are respectively connected to the reference standard 2 and the tested transformer 4, and the reference standard 2 is connected to the tested transformer 4 and respectively connected to the error tester 3.

The power generator 1 can generate a high-current AC-DC composite signal or a half-sine wave signal, and apply the produced signal to the measured current transformer 4 and the reference standard 2;

The reference standard device 2 can accurately convert the AC and DC components in the measured large current signal into a small current or small voltage signal, and input it to the error tester 3 as a reference signal;

The error tester 3 samples the reference signal output by the reference standard 2 and the measured signal output by the measured current transformer 4 synchronously, converts them into two sets of digital signals, and uses digital signal processing technology to calculate and obtain the final measurement results.

The above-mentioned current transformer DC and even harmonics affect the measurement device. When the power generator generates an AC-DC composite signal, its principle is shown in Figure 2, including an AC current generator for outputting a large AC current. The source 5 and a DC current source 6 for outputting DC current form an AC-DC composite signal on a branch circuit where the two are connected together. In Fig. 2, the capacitor C has the characteristics of blocking DC and AC, which can prevent the saturation of the current booster and reduce the distortion of the primary current. The function of the inductance L is to increase the impedance of the branch circuit of the DC source by using the characteristics of the inductor through the DC and resisting the AC, thereby achieving the purpose of preventing the DC source from being burned.

The above-mentioned current transformer DC and even harmonics affect the measuring device. When the power generator produces a half-sine wave signal, its principle is as shown in accompanying drawing 3, including an alternating current source 5, a diode, a resistor, etc., and the alternating current After the current is half-wave rectified, a half-wave sinusoidal signal containing only DC and even harmonics is formed. The type of the two rectifier diodes in attached drawing 3 should be the same, R is the ballast resistor, its function is to reduce the influence of the voltage drop of the rectifier diode on the loop current, R _B is the balance resistor, and its resistance value is approximately equal to the reference standard and the measured The sum of the primary impedances of the transformers.

The reference standard adopts AC and DC general-purpose measuring equipment such as precision shunts and zero-flux sensors. The accuracy of the measured current transformer is up to 0.2S level, so the reference standard needs to meet the requirements that the amplitude error of DC and AC is less than 0.05%, and the phase error of power frequency AC is less than 2 points. By comparing the existing current measurement principles, there are two kinds of precision shunts and zero-flux current sensors with AC and DC general functions and high accuracy. In this case, FLUKE A40B type precision shunt and LEM ITZ type zero magnetic flux sensor are selected as reference standards. The current range of the A40B type shunt is from 0.1mA to 100A, the bandwidth is from DC to 100kHz, the rated output voltage is 0.8V, and the accuracy can reach 0.001 class. The rated current of the ITZ zero-flux sensor can reach up to 24000A, the DC measurement accuracy is 2×10‐6, and the AC measurement accuracy is 0.02%.

The error tester includes a sampling resistor, a dual-channel data acquisition card and a data processing module. In this case, A40B shunts with rated currents of 1A and 5A are used as sampling resistors to convert the current signals output by the measured current transformer and the reference standard (when the zero magnetic flux sensor is selected as the reference standard) into voltage signals. In this case, the NI 5922 digitizer is used as a dual-channel synchronous data acquisition card with a resolution of 24bit and a sampling rate of 500k/s, which can simultaneously sample the reference signal and the signal under test. In this case, the LabView program is used as the software, which initializes the NI 5922, and applies the FFT function to the collected data for Fourier transformation to obtain information such as effective value, DC content, fundamental wave amplitude, and fundamental wave phase. By comparing the difference between the measured values of the reference standard channel and the measured transformer channel, the required effective value error, fundamental wave amplitude error, fundamental wave phase error and other information can be obtained.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present utility model rather than to limit the scope of protection thereof. Although the application has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: After reading this application, those skilled in the art can still make various changes, modifications or equivalent replacements to the specific implementation of the application, but these changes, modifications or equivalent replacements are all within the protection scope of the pending claims of the application.

Claims (7)

1. a current transformer error measurement apparatus, it is characterised in that: described device includes power source generator (1), reference standard (2) and error testing instrument (3)；Described power source generator (1) is marked with reference respectively Quasi-device (2) and tested transformer (4) connect, and described error testing instrument (3) is with reference standard (2) even Connecing, and be provided with the connection end being connected with tested transformer (4), described reference standard (2) is provided with tested The connection end that transformer (4) connects, described measurement apparatus uses alternating current-direct current composite signal or half-sinusoid signal Both of which.

Measurement apparatus the most according to claim 1, it is characterised in that described device uses alternating current-direct current synthesis During signal mode, described power source generator (1) includes ac current source (5) and DC current source (6), institute State ac current source (5) and include that pressure regulator and current lifting device, one end of described current lifting device are connected with electric capacity C, institute The other end stating electric capacity C is connected with inductance L, the other end of described inductance L and one end of DC current source (6) Connecting, the other end of described current lifting device is connected with the other end of described DC current source (6).

Measurement apparatus the most according to claim 1, it is characterised in that described device uses half-sinusoid letter During number pattern, described power source generator (1) includes ac current source (5) and commutation diode, described exchange Current source (5) includes that pressure regulator and current lifting device, one end of described current lifting device are connected with resistance R, described resistance R The other end be connected with the anode of the first diode and the negative electrode of the second diode respectively, another of described current lifting device End and resistance R_BOne end connect, described resistance R_BThe other end and the second diode anode connect.

Measurement apparatus the most according to claim 1, it is characterised in that described reference standard (2) is straight Stream, the amplitude error of exchange are less than 0.05%, and industrial frequency AC phase error is less than 2 points.

Measurement apparatus the most according to claim 1, it is characterised in that described error testing instrument (3) is wrapped Include sampling resistor, double channel data acquisition card and data processing module.

Measurement apparatus the most according to claim 5, it is characterised in that described sampling resistor rated current is 1A or 5A, error is less than 0.01%.

Measurement apparatus the most according to claim 5, it is characterised in that described double channel data acquisition card Resolution is not less than 24bit.