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Method for detecting breakage of PT neutral line

A neutral line disconnection and sub-harmonic technology, applied in the field of power system, can solve problems such as voltage component malfunction, phase voltage change of protection device, component malfunction, etc., to improve accuracy and prevent false blocking protection function. Effect

Inactive Publication Date: 2018-12-07
NR ELECTRIC CO LTD +1
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

When the PT neutral line is disconnected, the phase voltage of the protection device will change due to the potential drift of the neutral point, which may lead to misoperation of the zero sequence directional element and voltage element, and there are many similar accidents on site.
Chinese patent CN201110187854.1 discloses a method for detecting PT neutral line disconnection by using the third harmonic of the zero-sequence voltage to be greater than the floating threshold calculated based on the positive-sequence fundamental voltage. This method considers the PT neutral line disconnection The characteristic that the third harmonic content of the voltage is relatively large, but it does not consider that other working conditions may also lead to a large third harmonic content, so in some non-PT neutral line disconnection conditions, misjudgment of the line may occur
In this case, if only relying on the third harmonic content and the fundamental wave content to determine whether the PT neutral line is disconnected, it may be misjudged as a disconnection, and the relevant functions of the protection device are blocked, so that the protection device refuses to operate. increased risk

Method used

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  • Method for detecting breakage of PT neutral line

Examples

Experimental program
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Effect test

Embodiment 1

[0020] like figure 1 As shown, U1a, U1b, U1c, and U1n are the voltage outputs of the secondary side of the PT, and U2a, U2b, U2c, and U2n are the secondary voltage outputs of the small PT of the protection device, which are used for calculation by the protection device.

[0021] Calculating U2a, U2b, U2c by Fourier method can get the fundamental wave voltage and the 2nd, 3rd, 4th harmonic voltage, and then get the zero-sequence fundamental voltage 3U 0 , Positive sequence fundamental wave voltage U 1 , The third harmonic voltage of zero sequence voltage 3U 0_3harm .

[0022] Take certain values ​​for the proportional coefficient and the third harmonic content of the zero-sequence voltage in formula ①, such as taking K 1 = 0.2, U 3harm_unb =2V; According to the content of higher harmonics that may exist under different working conditions in the power grid, take a certain value for n. For example, it is known that the high-order harmonics in the power grid are mainly 6th and...

Embodiment 2

[0030] The specific parameters of the first criterion are the same as those in Embodiment 1.

[0031] Assuming that the PT is installed in another power grid different from that of Example 1, the main high-order harmonics in the power grid are 4th and below, and the content of high-order harmonics above 4th is very small, then n is set to 4; for each coefficient in formula ② Take definite values ​​respectively, such as taking K 2 = K 4 = 1.0. The specific implementation of the above two criteria is as follows:

[0032] 3U 0_3harm >0.2*U 1 +2V type③

[0033] 3U 0_3harm >(U A_2harm + U B_2harm + U C_2harm )+(U A_4harm + U B_4harm + U C_4harm ) formula ⑤

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Abstract

The invention discloses a method for detecting the breakage of a PT neutral line. The method comprises a step of calculating a positive sequence fundamental voltage and various higher-harmonic voltages of each phase according to voltage sampling values of A, B and C phases of a secondary side of a PT, a step of calculating a zero-sequence third-harmonic voltage according to the zero-sequence voltage sampling value of the secondary side of the PT, a step of calculating and obtaining a voltage threshold 1 according to the positive sequence fundamental voltage, a step of calculating and obtaininga voltage threshold 2 according to the various higher-harmonic voltages of each phase, and a step of reporting that the PT neutral line is broken after a delay when the zero-sequence third-harmonic voltage is larger than the voltage threshold 1 and the zero-sequence third-harmonic voltage is larger than the voltage threshold 2. By using the method, the breakage of the PT neutral line can be judged, when various higher-harmonic voltages are generated due to operations of no-load main transformer and the like in a system, besides third-harmonic content is large, other-harmonic content is also large, and the misjudgment of the breakage of the PT neutral line can be prevented.

Description

technical field [0001] The invention relates to a method for detecting disconnection of a PT neutral line in the field of power systems. Background technique [0002] PT disconnection is a common fault in the power system. PT disconnection can be divided into neutral line disconnection and non-neutral line disconnection according to the phase of the disconnection. The disconnection of the neutral line means the disconnection of the N line, and the disconnection of the non-neutral line means the disconnection of the A phase, B phase or C phase. At present, the research on non-neutral line disconnection is quite mature, and the protection device can judge whether non-neutral line disconnection occurs according to conditions such as zero-sequence voltage and positive-sequence voltage, but there are relatively few studies on neutral line disconnection . When the PT neutral line is disconnected, the phase voltage of the protection device will change due to the potential drift ...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): G01R31/02G01R31/08
CPCG01R31/086G01R31/50
Inventor 刘奎赵青春戴光武谢华徐晓春陆金凤沈军张洪喜
Owner NR ELECTRIC CO LTD
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