Judgement procedure for digital transformer differential protection to prevent TA secondary circuit failure from leading to mistaken operation

Abstract

The invention discloses a method for preventing differential protection misoperation of a digital transformer caused by such errors as short circuit, open circuit and etc. on the secondary circuit of a current transformer. Criterions for the errors in the TA secondary circuit are as follows: when a digital transformer protection device is running normally (a primary system accessed by the transformer does not go out of order), if the TA secondary circuit error is determined as that one- or two-phase current drops by 30 percent or higher, and difference current exists, then, the TA secondary circuit is determined as being out of order. On the premise of sudden current change: the current after the sudden change drops rather than increases, and the primary system has errors, or at least one-phase current will increase; therefore, one- or two-phase current of three-phase current drops by 30 percent or higher at the side; meanwhile, the three-phase current at other sides does not vary. If the conditions are met, the TA secondary circuit is determined as being out of order; after the TA secondary circuit goes out of order, an alarm signal is launched, and a latched or an unlatched difference protection outlet can be selected.

Description

technical field [0001] The present invention relates to the field of power systems, and more particularly to a method for relay protection. Background technique [0002] Current transformer (TA) secondary circuit faults include two types of secondary circuit open circuit and short circuit: [0003] TA secondary circuit open circuit includes: A, B, C three-phase one phase, two phases, or all three phases open circuit and N phase open circuit. [0004] TA secondary circuit short circuit includes: AN, BN, CN, AB, BC, CA, ABC, ABCN short circuit. [0005] In the digital transformer protection device, under normal operating conditions, the TA disconnection is judged by checking that one or two phases of all phases have no current and there is a difference current, that is, it is judged as TA disconnection. When there is a sudden change in current, the criteria are as follows: [0006] The current decreases (instead of increasing) after a sudden change; [0007] One or two pha...

AI Technical Summary

Problems solved by technology

[0030] However, in the digital transformer differential protection, there is still no reliable blocking measure for the short circuit of the TA secondary circuit that may cause the transformer differential protection to malfunction. Measures have been taken for the TA line: "One or two of the three-phase currents on this side have no current" as the TA disconnection criterion, but the criterion is not reasonable

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