Negative sequence overcurrent protection method for motor in small-current grounding system

Abstract

The invention discloses a negative sequence overcurrent protection method for a motor in a small-current grounding system. According to the negative sequence overcurrent protection method, by utilizing collected real-time A phase and C phase currents of a motor stator winding and the collected previous time sampling currents stored in a device and calling an offline calculated transformation coefficient, an A phase resultant current is obtained, and finally, a negative sequence current at the previous sampling time is calculated through the resultant current and the C phase current to serve asthe criterion of a protection action. Complicated complex operation is not involved in the negative sequence overcurrent protection method, and in the step needing complicated trigonometric operation, a result can be stored in the device through in-advance offline operation to be allowed to be called in the real-time calculation process. According to the negative sequence overcurrent protection method, calculation involved in real-time calculation is simple real-number algebraic operation, the algorithm principle is simple, calculation is easy to achieve, the operation amount is less, and theaction speed of the protected device can be increased greatly; and inertial delay of only one sampling time exists, and realtime performance is improved greatly.

Description

technical field [0001] The invention belongs to the technical field of electric power system relay protection, and in particular relates to a negative-sequence overcurrent protection method for a motor in a small current grounding system. Background technique [0002] When an asymmetrical short-circuit fault occurs in the power grid or an asymmetrical fault occurs in the motor body, a negative sequence current will flow through the stator winding. The negative-sequence magnetic field formed by the negative-sequence current has a large slip ratio with the rotor rotating in the positive direction, thereby inducing a large induced current in the rotor, resulting in a decrease in the output torque of the motor, and may burn the motor due to local overheating. [0003] Negative-sequence overcurrent protection of the motor is a necessary supplement to the overcurrent protection of the motor. It acts as a backup protection for the asymmetrical short-circuit fault of the motor, and ...

AI Technical Summary

Problems solved by technology

In this case, because only two-phase current can be collected, many protection devices on the market cannot realize the negative-sequence overcurrent protection of the motor by calculating the negative-sequence component of the three-phase current

If the negative sequence overcurrent protection is not configured, the possibility of reduced operating efficiency or local overheating and burnout of the motor due to asymmetrical faults is greatly increased

[0005] At present, the protection algorithms introduced in the papers "Research on Negative Sequence Algorithm in Motor Protection", "Filtration Method of Negative Sequence Current in Small Ground Current System with Two-phase CT Connection" and "Design of a Negative Sequence Current Measurement Device", Either calculate the B-phase current first, and then calculate the negative-sequence current through the three-phase current, or involve a large number of complex numbers and trigonometric operations in the real-time calculation, the calculation amount is large, or the real-time performance is poor, and it needs to go through 1 / 4 Inherent Computational Latency of Cycles

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