A Differential Protection Method Suitable for Variable Frequency Motor

Abstract

The invention discloses a differential protection method applicable to a variable-frequency motor. Phasor differential protection based on frequency tracking is combined with sampling value differential protection, whether a tripping outlet acts or not is determined through the combination result of the phasor differential protection and the sampling value differential protection. Sampling points are arranged at the generator terminal and neutral points of the variable-frequency motor respectively, the momentary values of currents on two sides are collected, the operation frequency of the motor is detected in a current tracking frequency manner, the sampling frequency is adjusted in real time, the sampling number of each cyclic wave is maintained to be unchanged, then the current phasors on two sides are calculated by using half-wave fourier algorithm, corresponding differential current and brake current are solved, distinguishing is carried out according to certain action characteristics, and meanwhile the sampling value differential motion without being influenced by frequency change is added, so that errors caused by a difference stream generated by the phasor differential protection during frequency discontinuity are avoided, and the anti-jamming capability of differential protection is improved.

Description

technical field [0001] The invention relates to how to realize the differential protection action logic of a frequency conversion motor in a high-voltage frequency conversion system, and belongs to the field of relay protection of electric power systems. Background technique [0002] With the gradual implementation of policies such as separation of power plants from power grids and grid bidding, it is imperative for power plants to reduce power consumption. Variable frequency motors are widely used in fan and pump loads in power plants because of their excellent speed regulation, starting and braking performance. The high-voltage frequency conversion technical transformation of the auxiliary equipment of the power plant can realize the soft start of the motor, reduce the starting current of the motor, and reduce the impact and mechanical wear on the insulation layer of the motor stator winding. At the same time, the traditional mechanical throttling adjustment method is not...

AI Technical Summary

Problems solved by technology

The frequency converter brings harmonics and heat to the motor, which has a certain impact on the long-term operation of the equipment

The traditional motor differential protection is designed based on the power frequency. After the inverter is installed, the current frequency is not 50Hz, and the differential protection has to be withdrawn during the frequency conversion operation. At this time, the protection of the motor only depends on the protection function of the inverter.

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