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An Improved Third Harmonic Stator Grounding Ratio Criterion

A harmonic stator and sub-harmonic technology, which is applied to the parts of emergency protection devices, electrical components, emergency protection detection, etc., can solve the problems of ratio criterion rejection, misjudgment, etc.

Active Publication Date: 2019-02-26
NARI TECH CO LTD
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  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

This method will lead to misjudgment that the neutral point PT is disconnected when the low-resistance grounding near the neutral point is caused, and the ratio criterion will be rejected.

Method used

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  • An Improved Third Harmonic Stator Grounding Ratio Criterion

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Embodiment Construction

[0024] The present invention will be further described below in conjunction with the accompanying drawings. The following examples are only used to illustrate the technical solution of the present invention more clearly, but not to limit the protection scope of the present invention.

[0025] In the microcomputer relay protection device, data collection and processing are all discrete, and the specific implementation of the present invention is described by taking the discrete mode applicable to the microcomputer protection as an example. Each sampling point of the microcomputer protection device adopts the improved third harmonic stator grounding ratio criterion, such as figure 1 shown, including the following steps:

[0026] 1) Take 10Hz as the fundamental wave, and use Fu's algorithm to extract the 150Hz components of the machine end and neutral point respectively.

[0027] 2) The ratio of the 150Hz component at the computer terminal to the 150Hz component at the neutral ...

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Abstract

The invention discloses improved third harmonic stator grounding ratio criteria. A third harmonic extraction method in the criteria is implemented through taking 10Hz as a fundamental wave and extracting a 150Hz component. Through the method, a 20Hz injection source serves as the second harmonic of 10Hz and is completely filtered. The extraction of a 150Hz component is not affected by a 20Hz component, and the150Hz component can be precisely extracted. In the criteria, when the 150Hz component of a neutral point is less than 0.2V, the criteria can achieve the correct distinguishing of PT linebreakage of the neutral point and a low-resistance grounding fault nearby the neutral point if no latch-up protection is carried out when the abrupt change of the 150Hz component of a machine end is greater than 0.2V.

Description

technical field [0001] The invention relates to an improved third harmonic stator grounding ratio criterion, which belongs to the field of electric power system relay protection. Background technique [0002] At present, the neutral point of synchronous motors such as large generators and condensers is not directly grounded. When a stator ground fault occurs, the current differential protection configured for these synchronous motors cannot reflect this type of fault sensitively due to the relatively small ground current. In order to reflect the stator grounding fault, synchronous motors are generally equipped with a separate stator grounding protection. There are two types of stator grounding protection currently configured, one is 100% stator grounding protection composed of fundamental wave zero-voltage stator grounding protection and third harmonic stator grounding protection protection; the other is injection stator ground protection. The third harmonic stator ground ...

Claims

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Application Information

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Patent Type & Authority Patents(China)
IPC IPC(8): H02H7/06H02H1/00
CPCH02H1/0007H02H7/06
Inventor 郑作伟李志坚潘书燕吴崇昊揭萍郝后堂谭凌王焕凤沈莹毛俊喜曾炳文万洛飞李蔚杨平怡
Owner NARI TECH CO LTD