Method for preventing wrong differential protection of motor and transformer caused by induced inrush current

Abstract

The invention discloses a method for preventing wrong differential protection of a motor and a transformer caused by induced inrush current. The method comprises the steps of detecting the direct component of each phase current of the motor and the transformer, if one phase or multiple phases are rapidly increased and each phase of differential current of differential protection is small than a starting fixed value in the afterward T1 time period, determining the condition that an outer fault and/or the induced inrush current occurs, and performing differential protection with the blocking ratio in the afterward T2 time period; during the blocking period, if the differential current and the phase current are synchronously rapidly increased, determining the internal fault and unblocking. The internal fault and induced inrush current (or external fault) can be distinguished by detecting whether the rapid increment of the direct current component of the phase current and the differential current occur synchronously or not, and the false operation of the ratio differential protection is prevented by a short blocking measure; if the internal fault occurs again in the blocking period, the unblocking is performed to handle the conversion fault. The method is simple, reliable and easy to realize, and the fixed value is still rectified as usual without affecting the sensitivity of the differential protection.

Description

technical field [0001] The invention belongs to the technical field of relay protection for main equipment in a power system, and relates to a method for preventing malfunction of differential protection of generators and transformers caused by inrush current. Background technique [0002] As the main protection of generators and transformers, differential protection can sensitively respond to the internal short-circuit fault of the unit, and is the key protection for the safe and stable operation of the unit. Such as figure 1 As shown, when a transformer is air-dropped and charged, it may produce a summation effect with another parallel or cascaded operating transformer, resulting in a summation inrush current in the operating transformer, thereby causing differential protection of the main transformer or generator Misoperation. [0003] Some preventive measures and criteria have been put forward for the main transformer protection misoperation caused by inrush current, s...

AI Technical Summary

Problems solved by technology

Although the inrush current is a through current for the differential of the generator, if the characteristics of the current transformers on both sides of the generator are inconsistent, the DC componen

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