Method for optionally cutting off fault point of double branch circuits at low voltage side of transformer

Abstract

The present invention belongs to a method for optionally cutting off a fault point of double branch circuits at the low voltage side of a transformer, which comprises the following steps of: (1) when earthed fault occurs, measuring instantaneous values of current I0 of an earthed neutral point and an triphase current of each branch at the low voltage side of the transformer; (2) calculating amplitude values of the I0 and zero-sequence current I01 and I02 of two branches at the lower voltage side of the transformer; (3) automatically analyzing the relation between the amplitude values of I0, I01 and I02; and (4) according to an analyzing result of the step (3), enabling a corresponding circuit breaker to actuate by sections and time delay to complete the cutoff of the failed branch. The method carries out discrimination by utilizing the distribution feature of zero-sequence fault current flowing through two branches at the low voltage side of the transformer when low-resistance earthed fault occurs and intelligently identifies the faulted branch circuit at the low voltage side of the transformer; and compared with the prior protection proposal, the method effectively shortens the load cutting range, improves the reliability of power supply for a user, reduces the blackout range caused when the earthed fault is earthed and changed into zero-sequence protecting action and protects the power load as large as possible.

Description

technical field [0001] The invention belongs to the technical field of zero-sequence current protection of grounded transformers on the low-voltage side of transformers, in particular to a method for selectively removing fault points in double-branch lines on the low-voltage side of transformers. Background technique [0002] With the rapid growth of power load, the grid scale in the city is constantly expanding and extending. Restricted by urban planning, environmental protection and site conditions, urban substations are increasingly using cable feeders, so that the 10kV system The single-phase-to-ground capacitive current has increased significantly. In order to suppress the overvoltage amplitude generated when the single-phase is grounded, more and more 10kV power grids have begun to use low-resistance grounding wiring. The grounding fault current is about 400-600A. This wiring method It is to isolate the grounding fault by the corresponding zero-sequence protection acco...

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Problems solved by technology

This method has formed a good protection for the single-branch line on the low-voltage side of the transformer, and can cut off the fault point in time to protect other equipment. However, the current common structure is that there are two branches on the low-voltage side of the transformer. At this time, if the existing grounding transformer is still applied In the zero-sequence current protection scheme, the action of the first time limit of the zero-sequence current protection is not selective. When a fault occurs, the section circuit breakers of each branch of the transformer are directly cut off, and the electrical equipment in the non-faulty branch is cut off at the same time virtually. The power outage range of the ground fault is expanded, which leads to unnecessary load loss on the bus bar of the non-faulty branch on the low-voltage side of the transformer, which reduces the reliability of power supply to users and damages the interests of users

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