CN102195273A - Wire-breaking judgment method in voltage transformer loop - Google Patents

Abstract

The invention discloses a wire-breaking judgment method in a voltage transformer loop, which comprises the steps of: measuring a three-phase voltage of a voltage transformer (TV) by a protecting device, calculating a third harmonic amplitude of a zero sequence voltage produced by the TV and a positive sequence voltage amplitude; when the ratio of the third harmonic amplitude to the positive sequence voltage amplitude exceeds the set ratio constant value, judging that a neutral wire of the TV loop is broken, wherein whether the neutral wire of the TV loop is broken is judged according to the criteria as follows: in the formula I (described in the specification), 3U0_3w represents the third harmonic amplitude of the zero sequence voltage produced by the TV, U1 represents the TV positive sequence voltage amplitude, and kset represents the ratio constant value. The third harmonic amplitude of the zero sequence voltage produced by the TV is used for judging that the threshold is self-adaptively adjusted along with the positive sequence voltage, thus the wire-breaking judgment method can be used for really reflecting the characteristics of breaking of the neutral wire of the TV loop, has small computational load, and is easy for program realization.

Description

A kind of voltage transformer circuit center line broken string method of discrimination

Technical field

The present invention relates to field of power, relate more specifically to the method for discrimination that the center line broken string appears in voltage transformer circuit in the voltage measurement circuit, and relate to the protective device of using this method of discrimination.

Background technology

Extensive use voltage transformer (TV) in the electric power system, when TV loop center line broke, because the neutral point potential drifting, the phase voltage of protective device can change, thereby may cause protecting incorrect operation.

Patent application " CN200710176913.9 " has proposed a kind of method of utilizing triple-frequency harmonics to detect TV loop center line broken string, calculate the triple-frequency harmonics amplitude in TV three-phase voltage and the self-produced residual voltage, when the continuous 30s of triple-frequency harmonics amplitude of arbitrary voltage surpasses 4V, be judged to TV loop center line broken string.Test shows that during TV loop center line broken string, the triple-frequency harmonics in TV three-phase voltage and the self-produced residual voltage is relevant with the original edge voltage size, and being provided with fixedly, threshold can not react the electric characteristic that TV loop center line breaks comprehensively.

Summary of the invention

The objective of the invention is: the voltage transformer circuit center line broken string method of discrimination that a kind of energy actual response TV loop center line broken string feature is provided, differentiate threshold along with the positive sequence voltage self adaptation of TV is adjusted by the self-produced residual voltage triple-frequency harmonics of TV, the feature of actual response TV loop center line broken string.

During normal the operation, triple-frequency harmonics content is very little in the TV three-phase voltage, and self-produced residual voltage triple-frequency harmonics amplitude is also very little; And when broken string appears in the center line in TV loop, all contain triple-frequency harmonics in the detected three-phase voltage of protective device, and the direction of third harmonic voltage is identical, contain bigger triple-frequency harmonics in the self-produced residual voltage.

The technical scheme that the present invention takes is: voltage transformer circuit center line broken string method of discrimination; protective device is gathered the three-phase voltage of voltage transformer TV; and the triple-frequency harmonics amplitude of the self-produced residual voltage of calculating voltage instrument transformer TV and positive sequence voltage amplitude; when both ratio surpasses the ratio definite value; be judged to TV loop center line broken string, the 20s that generally delays time moves in warning.

TV loop center line broken string criterion is as follows:

$\frac{{3U}_{0\_3w}}{U_1}>k_{\mathrm{set}}$ Formula 1

In the formula 1: 3U _{0_3w}Be the self-produced residual voltage triple-frequency harmonics of TV amplitude, U ₁Be TV positive sequence voltage amplitude, k _SetBe the ratio definite value, claim the ratio brake coefficient definite value again, generally adjusting is 0.1-0.5.

The protective device definite value of adjusting is k _Set, it is K that self-produced residual voltage triple-frequency harmonics is differentiated threshold _Set* U ₁, along with U ₁Variation, this differentiation threshold carries out the self adaptation adjustment thereupon.

The invention has the beneficial effects as follows: compare with the method for discrimination that " CN200710176913.9 " proposes, the self-produced residual voltage triple-frequency harmonics of the present invention is differentiated threshold along with the positive sequence voltage self adaptation is adjusted, the feature of energy actual response TV loop center line broken string, and operand is little, and the program that is easy to realizes.

Description of drawings

Fig. 1 is voltage transformer circuit center line broken string schematic diagram

Wherein, U1a, U1b, U1c, U1n are the voltage output of voltage transformer secondary side.U2a, U2b, U2c, U2n are the secondary voltage output of little instrument transformer in the protective device, calculate for protective device.

Embodiment

As shown in Figure 1, protective device is gathered TV secondary side three-phase voltage U 1a, U1b; U1c;, the little TV in protective device is converted to small voltage signal U2a, U2b; calculate behind the U2c; calculate TV self-produced residual voltage triple-frequency harmonics amplitude and positive sequence voltage amplitude, under the situation that does not have protection component to start, when both ratio surpasses the ratio definite value; be judged to TV loop center line broken string, time-delay 20s moves in warning.

TV loop center line broken string criterion is as follows:

$\frac{{3U}_{0\_3w}}{U_1}>k_{\mathrm{set}}$ Formula 1

In the formula 1: 3U _{0_3w}Be the self-produced residual voltage triple-frequency harmonics of TV amplitude, U ₁Be TV positive sequence voltage amplitude, k _SetBe the ratio brake coefficient definite value, generally adjusting is 0.1-0.5.

Claims (2)

1. differentiate the method that the voltage transformer circuit center line breaks for one kind; it is characterized in that: protective device is gathered the three-phase voltage of voltage transformer TV; calculate the triple-frequency harmonics amplitude and the positive sequence voltage amplitude of the self-produced residual voltage of TV; when both ratio surpasses the certain ratio definite value, be judged to TV loop center line broken string:

TV loop center line broken string criterion is as follows:

$\frac{3U_{0\_3w}}{U_1}>k_{\mathrm{set}}$ Formula 1

In the formula 1: 3U _{0_3 ω}Be the self-produced residual voltage triple-frequency harmonics of TV amplitude, U ₁Be TV positive sequence voltage amplitude, k _SetBe the ratio definite value.

2. a kind of method of discrimination of differentiating voltage transformer circuit center line broken string as claimed in claim 1 is characterized in that: the coefficient of ratio k in the formula 1 _SetAdjust and be 0.1-0.5.

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