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Grounded fault selecting and protecting method for grouded system with small current

A low-current grounding and grounding fault technology, applied in emergency protection circuit devices, electrical components, etc., can solve problems such as being susceptible to load changes, limited accuracy and operational reliability, and unfavorable applications.

Inactive Publication Date: 2005-07-27
CHANGSHA UNIVERSITY OF SCIENCE AND TECHNOLOGY
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AI Technical Summary

Problems solved by technology

The ground fault protection method based on the negative sequence current variation has high sensitivity, but is easily affected by load changes
The accuracy and operational reliability of the existing grounding protection methods for small current grounding systems are limited. Most of the grounding protection methods use the comparison of the measured quantities of each outgoing line, which is difficult to implement on the field terminal unit FTU of power distribution automation, which is not conducive to the distribution system. Application in electric automation

Method used

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  • Grounded fault selecting and protecting method for grouded system with small current
  • Grounded fault selecting and protecting method for grouded system with small current
  • Grounded fault selecting and protecting method for grouded system with small current

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Embodiment Construction

[0102] This protection method needs to measure three-phase current, three-phase voltage and zero-sequence voltage, and is suitable for realization on a hardware platform such as a microcomputer line protection device or a distribution automation field terminal unit FTU.

[0103] image 3 It is an FTU device, provided by Ningbo Tianan Group, and implemented by digital signal processor TMS320F206. The hardware structure principle is as follows Figure 4 shown. Using 14-bit AD conversion, 32 points per power frequency cycle to collect analog quantities such as three-phase voltage, three-phase current, zero-sequence voltage and zero-sequence current. Calculate the effective value of the zero-sequence voltage. When the zero-sequence voltage is greater than the set value (10% phase voltage), it is judged that a ground fault has occurred in the distribution network. The moment when the zero-sequence voltage suddenly changes is the time when the fault occurs. Calculate the phase-to-...

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Abstract

The method includes following steps: the zero sequence voltage, phase voltage and phase current are monitored on line; when the zero voltage is more than setting value, the system is determined in failure; the difference current between phases is defined as the 0.5 difference between this phase current variation and sum of other two phases current variation; the calculating resistance is defined as the ratio of the phase voltage after failure to difference current between phases based on this phase current; the calculating resistance of feed line is calculated; it is decided if the failure will be happened according to the value of calculating resistance; the calculating resistance value equals resistance value of earth failure; the failure line sends out failure signals.

Description

technical field [0001] The invention relates to the relay protection technology of electric power system, especially the single-phase ground fault line selection and protection of the neutral point not directly grounded system. Background technique [0002] The neutral point non-direct grounding system is referred to as the small current grounding system. When a single-phase grounding fault occurs, an overvoltage will be generated. If it is not cleared in time, it may cause cable explosion and other faults, affecting the safety and power quality of the power system. In the distribution network, the traditional method of tentatively pulling the switch one by one to find the faulty line is a waste of manpower and material resources, and has long been unable to meet the needs of the automation development of the power system. Application No. 91103633.4 titled "Detection Method and Device for Small Current Grounding" discloses a method for comparing the magnitude of AC harmonics...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): H02H7/26H02H7/28
Inventor 曾祥君陈伟乐马洪江李泽文王媛媛杨廷方
Owner CHANGSHA UNIVERSITY OF SCIENCE AND TECHNOLOGY
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