Main transformer zero-sequence current protection test method

Abstract

The invention discloses a main transformer zero-sequence current protection test method. The method comprises the following steps of: (1) grounding a single phase of a high-voltage side of a main transformer, and simulating a fault outside a zero-sequence differential region of the main transformer; (2) temporarily reducing a main transformer zero-sequence differential protection action constant value and temporarily reducing a main transformer zero-sequence overcurrent protection constant value; (3) checking the zero sequence CT polarity correctness of the main transformer on a protection device by using the current formed by the residual magnetism of a unit; and (4) rising the current so as to check the zero-sequence over-current protection action of the protection device. According to the test method, whether the polarity of a zero-sequence CT is correct or not is verified by simulating the polarity reverse connection condition of a zero-sequence CT loop and checking the action conditions of zero-sequence differential protection and zero-sequence over-current protection only through one-time current rising operation, the test logic is strict, the result is reliable, operation is easy, external wiring does not need to be changed, the risks of CT open circuit and wrong wiring do not exist, the life safety of workers is ensured, and a unit starting test is smoothly carried out.

Description

technical field [0001] The invention belongs to the field of electrical technology, and in particular relates to a test method for zero-sequence current protection of a main transformer. Background technique [0002] If a grounding short circuit occurs in the neutral point direct grounding system, a large zero-sequence current will be generated, and the zero-sequence current component is used to form a protection, which can be used as a main grounding short-circuit protection. There is no zero-sequence component generated during normal operation and system oscillation, so it has better sensitivity. Main transformer zero-sequence current protection includes zero-sequence differential protection and zero-sequence overcurrent protection. There is a zero-sequence differential protection for the ground fault on the high-voltage side of the main transformer. The zero-sequence overcurrent protection is mainly used as a backup protection for ground faults when the neutral point of ...

AI Technical Summary

Problems solved by technology

There is a zero-sequence differential protection for the ground fault on the high-voltage side of the main transformer. The zero-sequence overcurrent protection is mainly used as a backup protection for ground faults when the neutral point of the transformer is grounded. To work normally, the zero-sequence current protection of the main transformer must be used before putting into operation. The primary current checks the polarity of the secondary circuit of the relevant current connected to the protection device to ensure that the polarity is correct. Since the zero-sequence differential protection uses the calculation of the zero-sequence current to obtain the zero-sequence differential current to judge the protection action behavior, so in the electrical It is necessary to simulate a ground fault during the entire start-up test to judge the correctness of the current polarity. According to the traditional method, it is necessary to repeatedly increase the current four times to fully verify the correctness of zero-sequence differential protection and zero-sequence overcurrent protection. During the test process Changing the wiring has the risk of CT open circuit, miswiring, etc., and delays the start-up test progress of the unit

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