RU2580410C1 - Device for measuring high currents - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: invention relates to electrical engineering and power engineering, namely to devices for measurement of currents and can be used for monitoring and determining the shape of current flowing in circuits of high-voltage transmission lines. Device for measurement of large currents contains current-collecting rod connected directly to the measuring circuit to support a contactless current transformer and measuring current shunt. Contactless current transformer is connected to the first analogue-to-digital converter, and the measuring current shunt is connected to the second analogue-to-digital converter. To the first analogue-to-digital converter first unit of fast Fourier transform is connected. To the second analogue-to-digital converter a comparator unit and second Fast Fourier transform unit are connected, the output of the latter comprises level detector connected to the first multiplying unit whose input is connected to the output of first fast Fourier transform unit. First multiplier output is connected to the inverse Fourier transformation, which is connected to the first input of the second multiplier unit which second input is connected to the output of comparator unit. Second multiplier is connected with comparator and with display.

EFFECT: technical result prevents sources of pulse interference, minimises parasitic spectral components, including high-frequency and expands the spectral range of measured currents.

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Description

The invention relates to electrical engineering and electric power, in particular to devices for measuring currents and can be used to control and determine the shape of the current flowing in the chains of high-voltage transmission lines.

A device for measuring high currents [RU 2229137 C2, IPC 7 G01R 19/00, publ. 05/20/2004], containing three current splitters, which are calibrated conductors connected through a transformer. The conductors are located in the ″ window ″ of the current transformer counter-parallel, forming the primary winding of the current transformer, and create the resulting magnetic flux proportional to the difference in magnetic flux induced by the currents of the branch branches. The conductors have the same cross section and are fixed inseparably by means of linear clamps, which excludes the influence of transition resistance during connections.

The disadvantages of this device are the significant weight and size parameters of the splitter required for measuring high currents, low temporal stability due to corrosion of the splitter contacts, and the need to use larger magnetic cores.

Closest to the proposed device is to compensate for the error of the current transformer [RU 2449296 C1, IPC G01R 19/00 (2006.01), publ. 04/27/2012], comprising a current transformer, a measuring shunt included in the secondary circuit of the current transformer, and an integrator, the first input of which is connected in parallel with the measuring shunt. The input of the bipolar relay body is connected to the output of the integrator, the first input of the detector of opposite polarity of the signals is connected in parallel with the measuring shunt, and the second input is connected to the output of the integrator. The first input of the AND gate which is connected to the output of the bipolar relay element, and the second input is connected to the output of the detector for multi-polarity signals. The input of the additional voltage block is connected to the output of the AND gate. The auxiliary voltage unit is connected in series with the measuring shunt and is connected to the terminal of the secondary winding of the current transformer. The integrator is implemented with an input multiplier-adder, and its second input is connected to the output of the secondary winding of the current transformer.

In this device, the auxiliary voltage unit operates in a pulsed mode, which leads to the appearance of spurious spectral components in the signal and limits the frequency range of the measured currents.

The objective of the invention is the expansion of the arsenal of funds for similar purposes.

The problem is solved due to the fact that the device for measuring high currents, as in the prototype, contains a current transformer and a measuring shunt.

According to the invention, the collector rod is connected directly to the measuring circuit, on which a contactless current transformer and a measuring current shunt are mounted. The non-contact current transformer is connected to the first analog-to-digital converter, and the measuring current shunt is connected to the second analog-to-digital converter. The first fast Fourier transform unit is connected to the first analog-to-digital converter. The comparison unit and the second fast Fourier transform unit are connected to the second analog-to-digital converter, the output of which is connected to a level detector connected to the first multiplication unit, the input of which is connected to the output of the first fast Fourier transform unit. The output of the first multiplication block is connected to the inverse Fourier transform block, which is connected to the first input of the second multiplication block, the second input of which is connected to the output of the comparison block. The second multiplication unit is connected to the comparison unit and to the display.

The proposed device allows you to measure large currents by digitizing the signals from the outputs of the contactless current transformer and the measuring current shunt (a) in FIG. 1) and applying the fast Fourier transform to these signals (b) in FIG. one). The subsequent comparison of the spectra minimizes the distortions introduced by the saturation of the core of the contactless current transformer. Next, the signal is restored from its spectrum, its large-scale conversion and visualization (c) in FIG. one). Thus, in comparison with the prototype, the sources of impulse noise are eliminated, spurious spectral components, including high-frequency ones, are minimized, and the spectral range of the measured currents is expanded.

The advantage of the proposed device during its implementation is the ability to use common models of contactless current transformers, non-linear distortions of the output signals of which are compensated by the use of linear measuring current shunts.

In FIG. Figure 1 shows the timing diagrams of the main signals, where a) is the nonlinearly distorted signal from the output of the current transformer and the linearly distorted signal from the output of the measuring current shunt; b) the spectrum of a nonlinearly distorted signal from the output of the current transformer and the spectrum of the linearly distorted signal from the output of the measuring current shunt; c) is the resulting adjusted output signal.

In FIG. 2 shows a structural diagram of a device for measuring high currents.

A device for measuring high currents contains a collector rod 1, which is connected directly to the measuring circuit, on which a contactless current transformer 2 and a measuring current shunt 3 are mounted. The signal recording and processing unit 4 (BROS) contains the first analog-to-digital converter 5 (ADC1), which is connected to the first fast Fourier transform unit 6 (BPF1), the second analog-to-digital converter 7 (ADC2), to which the second fast Fourier transform unit 8 (FFT2) and the comparison unit 9 (BS) are connected. The level detector 10 (UD) is connected to the output of the second block of fast Fourier transform 8 (BPF2), to the first block of multiplication 11 (BU1), the input of which is connected to the output of the first block of fast Fourier transform 6 (BPF1). The output of the first multiplication block 11 (BU1) is connected to the inverse Fourier transform block 12 (BOPF), which is connected to the first input of the second multiplication block 13 (BU2), the second input of which is connected to the output of the comparison unit 9 (BS). The second unit of multiplication 13 (BU2) is connected to the display 14 (D) and to the comparison unit 9 (BS). Contactless current transformer 2 is connected to the first analog-to-digital converter 5 (ADC1), and the measuring current shunt 3 is connected to the second analog-to-digital converter 7 (ADC2).

The first and second analog-to-digital converters 5 (ADC1) and 7 (ADC2) are made using analog-to-digital converters AD7693. Blocks of fast Fourier transform 6 (FFT1), 8 (FFT2), as well as inverse Fourier transform 12 (FFT) are made using digital signal processors ADSP-21991. The multiplication blocks 11 (BU1), 10 (BU2), comparisons 9 (BS) and level detector 13 (UD) are made using microcontrollers ADSP-TS201S. As a measuring shunt 3 used current shunt Fluke A40V. As current transformer 2, a Lilco 13 W0100 current transformer is used.

The measured current i flowing along the collector rod 1 is converted by a current transformer 2 to a voltage U _T , and a measuring shunt 3 to voltage U _W. The voltage U _T undergoes non-linear distortion caused by saturation of the magnetic core of the current transformer 2, and the voltage U _W can undergo linear distortion caused by the frequency dependence of the impedance of the shunt 3. Then the voltage U _T and U _W are digitized using analog-to-digital converters 5 (ADC1) and 7 (ADC2), respectively. The resulting current samples {U _Т , _i } and {U _{Ш, i} }, where i is the number of the number in the sample, using the fast Fourier transform blocks 6 (FFT1) and 8 (FFT2), respectively, is subjected to the Fourier transform procedure. As a result, arrays of spectral components of the signal of the current transformer 2 {S _T , _j } and measuring shunt 3 {S _{Ш, j} } are obtained, where j is the number of the spectral component in the sample. After that, the spectral components of the signal of the measuring current shunt are fed to the input of the level detector 10 (UD), where each nonzero component is brought to a unit level:

{S2 _{Ш, j} } = 0 if {S _{Ш, j} } = 0 and {S _{Ш, j} } = 1 if $$\left\{\left|S_{W,j}\right|\right\}>0.$$

The resulting arrays of numbers {S _{T, j} } and {S2 _{W, j} } are multiplied in the multiplication block 11 (BU1) and the result of this operation {S2 _{T, j} } is subjected to the inverse Fourier transform in the corresponding block 12 (BOPF). The restored signal from the output of the multiplication block 13 (BU2) is fed to the input of the comparison unit 9 (BS), the second input of which receives the signal from the output of the second analog-to-digital converter 7 (ADC2). When these signals are different, the comparison unit 9 (BS) generates a control action on the multiplication unit (BU2), which performs a large-scale signal conversion. When these signals coincide, the multiplication unit (BU2) stops the scale conversion of the signal and the restored signal is displayed on display 14 (D).

Thus, the nonlinear distortions introduced into the measured signal by saturation of the magnetic core of current transformer 2 are minimized.

By step-by-step approximations, the signal levels are linearly aligned from the output of the inverse Fourier transform block 12 (BFT) and analog-to-digital transform 7 (ADC2). To do this, use the comparison blocks 9 (BS) and multiplication 13 (BU).

As a result, a resulting output signal with minimized non-linear distortions is obtained, which is directly proportional to the measured current i.

Claims (1)

A device for measuring high currents, comprising a current transformer and a measuring shunt, characterized in that the collector rod is connected directly to the measuring circuit, on which a non-contact current transformer and a measuring current shunt are mounted, wherein the non-contact current transformer is connected to the first analog-to-digital converter, and the measuring the current shunt is connected to the second analog-to-digital converter, the first Fur fast block is connected to the first analog-to-digital converter ye, the comparison unit and the second fast Fourier transform unit are connected to the second analog-to-digital converter, the output of which is connected to a level detector connected to the first multiplication unit, the input of which is connected to the output of the first fast Fourier transform unit, and the output of the first multiplication unit is connected to the unit the inverse Fourier transform, which is connected to the first input of the second multiplication unit, the second input of which is connected to the output of the comparison unit, and the second multiplication unit is connected to the comparison unit and display.

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