Earth fault signal measuring method and protective device for ungrounded system

Abstract

The invention discloses an earth fault signal measuring method and a protective device for an ungrounded system. According to the method, an outlet of a cable line and measuring points of fault signals are arranged at the end of a shield ground wire of a cable head, a special-purpose earth fault current lead is laid at the end, and a cross-core open current transformer and a special-purpose lightning arrester are installed; an outlet of an overhead line and measuring points of fault signals are arranged at underground below a path formed by No. 0 to No. 6 poles of the outlet, an earth electrode is buried in the underground, an earth current acquisition wire is laid to connect to the earth electrode, and a cross-core open current transformer and a special-purpose lightning arrester are installed. The protective device comprises a cable line single-phase ground protection unit, an overhead line single-phase ground protection unit, a ground protection current latching unit, a ground protection voltage latching unit, a digital analog converter and a display. The method and the protective device provided in the invention enable a line selection rate under the condition of a line earth fault to be improved and the fault to be dealt with rapidly.

Description

technical field [0001] The invention relates to a measurement method and a protection device for a grounding fault signal of a power system, and is particularly suitable for measuring and protecting a grounding fault signal of a transmission line of an ungrounded system. Background technique [0002] At present, in the power transmission and distribution lines of different levels in the power system, the transmission and distribution lines below 35KV usually operate in the mode of small current grounding (grounding through the arc suppressing coil) and non-grounding mode. More than 80% of the total, the transmission and distribution lines operated in ungrounded mode, after a single-phase ground fault occurs, the fault phase voltage of the system decreases, and the non-fault phase voltage increases. The equipment poses a threat, because there is more than one power transmission and distribution line in the substation, and the regulations require that the faulty line be found ...

AI Technical Summary

Problems solved by technology

[0003] Due to the wide variety of ground faults, the ground fault line selection methods used at home and abroad are also different. The application number is 91103633.4, and the name is "Small current grounding detection method and device". Method to identify faults; application number 94106374.7, titled "Single Earthing Protection Method and Device for Small Current System" Method” patent, which uses the calculation of the negative sequence current variation of each feeder, and judges the fault according to the magnitude, direction or energy function of the negative sequence current; the fault signal source of each of the above methods is selected from the common current transformer and voltage of each outgoing line Transformer, the resolution of identifying the faulty line is low

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