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A method for detecting disconnection of pt neutral wire

A neutral line disconnection and sub-harmonic technology, applied in the field of power systems, can solve problems such as prone to misjudgment and insufficient sensitivity, and achieve accurate judgment and sensitive and reliable criteria

Active Publication Date: 2011-12-21
NR ELECTRIC CO LTD +2
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

Because it adopts the criterion of fixed threshold, when the positive sequence voltage value is small, the sensitivity of the criterion is not enough, and when the third harmonic appears in the system, it is easy to misjudgment

Method used

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  • A method for detecting disconnection of pt neutral wire
  • A method for detecting disconnection of pt neutral wire
  • A method for detecting disconnection of pt neutral wire

Examples

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Embodiment Construction

[0018] Combined with the description of the drawings, such as figure 1 As shown, U1a, U1b, U1c, and U1n are the voltage outputs of the secondary side of the PT. U2a, U2b, U2c, and U2n are the secondary voltage output of the small PT of the protection device, which are used for calculation by the protection device.

[0019] image 3 The left column (a) in the center is the excitation current and winding voltage waveform diagram and its harmonic analysis diagram when the normal connection is made; the right column diagram (b) is the excitation current and winding voltage waveform diagram and its harmonic analysis diagram when the neutral line is disconnected picture.

[0020] Calculate the third harmonic content of each phase of ABC on the secondary side of the PT or the third harmonic content in the zero-sequence voltage by the Fourier algorithm. When the third harmonic content of the zero-sequence voltage is greater than the floating threshold, the PT neutral wire is discon...

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Abstract

The invention discloses a method for detecting PT neutral line failure. Positive-sequence fundamental wave voltage is calculated according to ABC three-phase sampling values of a PT secondary side, zero-sequence third harmonic voltage is calculated according to a zero-sequence voltage sampling value of a PT secondary side, and when the zero-sequence third harmonic voltage is greater than a floating threshold and third harmonic in one phase or multiple phases is greater than the floating threshold when the third harmonic content of each phase of voltage of the PT secondary side is calculated in a Fourier algorithm, the PT neutral line failure is reported through delaying. When the neutral line failure appears between the PT secondary side and a protective device, excitation current of the neutral line can not flow so as to cause changes of excitation current in ABC three phases, and the third harmonic of each phase of measured voltage of the protective device can appear. The PT neutral line failure can be detected according to the third harmonic in the zero-sequence voltage.

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 (N line) and non-neutral line disconnection (ABC line) according to the phase of the disconnection. At present, the research on non-neutral line disconnection has been 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. However, there are relatively few studies on neutral wire breakage. 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 cause misoperation of the zero-sequence directional element and voltage element. There are many similar accidents on site. Chi...

Claims

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Application Information

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IPC IPC(8): G01R31/02
Inventor 刘东超张朝龙胡绍刚朱晓彤刘俊德刘君沈军张绍林
Owner NR ELECTRIC CO LTD
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