Locking method for preventing differential protection maloperation of transformer caused by sympathetic inrush current

Abstract

The invention provides a locking method for preventing differential protection maloperation of a transformer caused by sympathetic inrush current, which belongs to the technical field of electric power automation. The method comprises steps of calculating a three-phase differential current value of a transformer, judging whether a phase difference exists between a second harmonic phase and a double fundamental current phase in the differential current when the transformer generates sympathetic inrush current or not, when it is judged that the phase difference exists between the second harmonic phase in the differential current and the doouble fundamental current phase when the sympathetic inrush current occurs in the transformer, calculating the second harmonic proportion value when the sympathetic inrush current and the fault occur in the transformer, judging whether the second harmonic proportion value is not lower than a proportion coefficient Kd or not, when it is judged that the second harmonic proportion values are all lower than the proportion coefficient Kd, judging whether the current value of the differential current is not lower than a setting value Iset or not, and when judging that the current value of the differential current is lower than the setting value Iset, locking differential protection.

Description

technical field [0001] The invention relates to the technical field of electric power automation, in particular to a blocking method for preventing maloperation of transformer differential protection caused by inrush current. Background technique [0002] When two or more transformers are in parallel or cascaded operation, the excitation current generated by one of them during no-load switching will affect the normal operation of other transformers, which is the inrush current of transformers and inrush currents. The amplitude of the inrush current increases first and then decreases, the attenuation DC component is large and the attenuation speed is slower than the conventional inrush current, which slows down the attenuation of the inrush current of a single unit, making the attenuation rate of the sum current of the two very easy to cause the current transformer Transient saturation is usually opposite to the direction of the inrush current and the excitation inrush curren...

AI Technical Summary

Problems solved by technology

However, when the inrush current occurs, considering the saturation of the transformer CT, within one cycle of the no-load closing of the adjacent transformer, the second harmonic ratio of the operating transformer will be lower than the fixed value under the action of the inrush current, so that The ratios of the three-phase second harmonics are all higher than the fixed value when there is a fault. The traditional second harmonic braking method will fail to judge when the inrush current occurs, which will lead to the problem of refusal or malfunction of the differential protection of the transformer, and cause serious accidents in the power system.

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