变压器差动保护是电力变压器的主要保护手段之一差动保护的理论依据是基尔霍

Transformer differential protection is the theoretical basis for one of the main means of protection differential protection of power transformers is Kirchhoff's law. Good selectivity, high sensitivity and high speed mobility is mainly in generator differential protection and protection circuit applications. But for transformers, Kirchhoff's current law does not apply to its essence, this is mainly due to an internal magnetic circuit of contact, one of the sources unbalanced current differential protection is the transformer magnetizing current. Normal operation, the transformer magnetizing current is typically less than one percent of the rated current, the set values ​​of the differential protection of the transformer can accurately distinguish between internal and external faults. When the transformer overexcitation operation, the transformer magnetizing current up to the rated current level, which will cause the differential protection operation, thus the power transformer operating conditions are very complicated. With no load on the transformer or an external transformer short-circuit and the transformer voltage is cut suddenly restored, inrush current may correspond to the size of the short-circuit current, it is 6-8 times the rated current. Inrush current flowing through the power supply side resulting in an imbalance of current transformers on both sides, so that the differential circuit current imbalance appeared, which led to the malfunction of the differential protection. The author of the principles, advantages and disadvantages as well as the application of a variety of differential protection schemes are analyzed and evaluation in order to determine the correct method to identify transformer internal fault and magnetizing inrush current and further resolved due to the inrush current of the transformer differential protection often appear error the problem of action.

Transformer differential protection is one of the main protection means of power transformer differential protection is based on Kirchhoff's law. Good selectivity, high sensitivity and high-speed mobility are the main manifestations of differential protection in generator and line protection applications. But for transformers, Kirchhoff's current law does not apply to its essence, mainly because of the connection of the internal magnetic circuit, and one of the sources of the differential protection imbalance current is the transformer excitation current. During normal operation, the excitation current of the transformer is generally less than one percent of the rated current, so the setting of the differential protection value can accurately distinguish between the internal and external faults of the transformer. When the transformer is excitation running, the excitation current can reach the level of the transformer's rated current, which will cause the differential protection wrong action, so the operating conditions of the power transformer are very complex. When the transformer is empty and closed or the transformer external short circuit is removed and the transformer voltage is suddenly restored, the excitation surge can be equivalent to short-circuit current, which is 6-8 times the rated current. Excitation surgeflow through the power supply side causes an imbalance of current on both sides of the transformer, so an unbalanced current appears in the differential circuit, which leads to mismovement of differential protection. The author analyzes and evaluates the principles, advantages and disadvantages of various differential protection schemes and applications to determine the method of correctly identifying the internal fault of the transformer and the excitation surge and further solves the problem that the transformer differential protection is often misacted due to excitation surge.

Transformer differential protection is one of the main protection methods of power transformer. The theoretical basis of differential protection is Kirchhoff's law. Good selectivity, high sensitivity and high-speed mobility are the main performance of differential protection in the application of generator and line protection. But for the transformer, Kirchhoff's current law is not applicable to its essence, which is mainly due to the connection of internal magnetic circuit. One of the sources of unbalanced current of differential protection is the excitation current of transformer. In normal operation, the excitation current of transformer is generally lower than 1% of the rated current, so the setting of differential protection value can accurately distinguish the internal and external faults of transformer. When the transformer is in over excitation operation, the excitation current can reach the rated current level of the transformer, which will cause the misoperation of the differential protection, so the operation conditions of the power transformer are very complex. When no-load closing or external short-circuit of the transformer is removed and the voltage of the transformer suddenly recovers, the magnitude of inrush current can be equivalent to the short-circuit current, which is 6-8 times of the rated current. The inrush current flowing through the power supply side causes the current imbalance on both sides of the transformer, so the unbalanced current occurs in the differential circuit, which leads to the misoperation of the differential protection. This paper analyzes and evaluates the principle, advantages and disadvantages as well as the application of various differential protection schemes, so as to determine the correct method to identify the internal fault and inrush current of the transformer and further solve the problem that the inrush current often causes the transformer differential protection to malfunction.