Multi-component recombination current flashy flow judgment method of transformer and block relay

Abstract

The invention discloses a multi-component recombination current flashy flow block relay for identifying excitation flashy flow of a transformer, aiming at solving the problems of differential protection malfunction caused by excitation flashy flow during air delivery and rapid action of differential protection when a turn-to-turn fault occurs. The invention provides a multi-component recombination current flashy flow block relay which consists of sample current selection of the flashy flow, three-time harmonic infeed scheme, an electric scheme of the current harmonic ratio and self-adaptive flashy flow block criteria, wherein the action logic diagram of the relay is shown in the attached figure. The test result indicates that the relay has good sensitivity, safety and rapidness. The invention also discloses a recombination current flashy flow judgment method.

Description

technical field [0001] The invention relates to the field of transformer protection of relay protection technology, in particular to a transformer surge current blocking relay. Background technique [0002] At present, the differential protection of transformers mainly solves two problems in practice: one is to identify the inrush current and fault current; the other is to distinguish external faults from internal faults. The differential protection of transformers can better distinguish external faults and internal faults to a certain extent, but there are still some shortcomings in the identification of inrush current. [0003] At present, the current waveform is mainly used as the main basis for judging the excitation inrush current and fault current. Among various excitation inrush braking schemes, the second harmonic braking is relatively mature and reliable. The protection of main transformers at home and abroad is basically equipped with this discrimination method. ...

AI Technical Summary

Problems solved by technology

Years of operating experience and tests have shown that there may be a phase with low second harmonic content, so the use of split-phase braking may easily lead to differential protection misoperation

[0009] "OR gate brake" may lead to differential protection refusal or delayed action

For example, when the transformer is closed on an internal single-phase fault, such as a phase A fault; phase B and phase C are non-fault phases, and there may be exciting inrush currents in phase B and phase C, and their second harmonic content is relatively high. Braking, therefore, will block the three-phase ratio differential, at this time, the fault phase A phase can not be exported

In addition, if the internal fault causes a phase with high second harmonic content due to various reasons, it may cause the differential protection to refuse to operate.

For example, current transformer CT saturation will lead to harmonic generation, and the system will also have harmonics when there is a fault

[0010] To sum up, the current second harmonic braking of inrush current has defects whether it adopts "separate phase braking" or "OR gate braking", which may easily cause misoperation and refusal of transformer differential protection protection.

Images