Differential protection device and algorithm for variable-frequency motor

Abstract

The invention relates to a differential protection device and algorithm for a variable-frequency motor. The device comprises a frequency converter, a motor, and current transformers CT1, CT2, and CT3.The CT1, the frequency converter, the CT2, the motor, and the CT3 are connected in series in this order. The frequency converter is provided with a bypass. The bypass is provided with a bypass circuit breaker. The turn-on signal contact of the bypass circuit breaker is connected to the differential protection device. The CT2 and the CT3 constitute differential protection when the bypass circuit breaker is turned off. The CT1 and the CT3 constitute differential protection when the bypass circuit breaker is turned on. The differential protection device has the beneficial effect of achieving differential protection in two modes of power-frequency operation and variable-frequency operation.

Description

technical field [0001] The present invention relates to the differential protection of frequency conversion motor, in particular to a differential protection device and algorithm of frequency conversion motor. Background technique [0002] The main equipment of a large-scale thermal power plant includes a boiler, a steam turbine, and a generator. The boiler is equipped with a primary fan, a secondary fan, and an induced draft fan. The steam turbine is equipped with a feed water pump. Both the fan and the water pump are driven by a large electric motor. While generating electricity, power plants also consume a large amount of electricity to maintain the operation of equipment, among which the electricity consumption of large electric motors accounts for about 85% of the total. In the context of energy-saving development, it is very common for large-scale thermal power plants to transform large-scale motors with frequency conversion. The purpose is to reduce the power consumpt...

AI Technical Summary

Problems solved by technology

The primary side currents of the two sets of current transformers are the same. Although the conditions for differential protection are met, the working voltage frequency is not the power frequency. The current transformer is designed to be used in the power frequency system, and the protection device is the same as the current transformer. , the current sampling circuit is designed to be used under power frequency, and it is also not applicable under non-power frequency conditions, and the reliability of the protection function is not sure

Some sites use this method to form differential protection, and frequent malfunctions occur during operation

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