A controllable harmonic elimination device for distribution network

Abstract

The invention discloses a controllable resonance suppression device for a distribution network. The device comprises a current transformer, a silicon controlled switch, a resonance suppression resistor and a control unit. The control unit consists of a current relay, a self latching relay, an amplifier, a subtraction device, a logic element and a current transformer secondary loop disconnection blocking unit. According to the invention, the transient energy flowing into the PT is absorbed based on short-time investment of the resonance suppression resistor and thus the state of the excitation winding of the PT is changed from a saturation state to a non-saturation state, thereby achieving an objective resonance suppression. When the system works normally, the silicon controlled switch enables the resonance suppression resistor to be in a short-circuit mode and the neutral point of the PT is grounded directly, thereby realizing the function of accurate measurement of a voltage to ground of a three-phase bus and a system zero sequence voltage. Besides, when a ground fault occurs and a circuit breaker operation is carried out, the three-phase PT neutral point will not bear the high voltage for long time because the short time of the neutral point access to the resonance suppression resistor, so that insulation of the PT neutral point is not damaged.

Description

technical field [0001] The patent of the present invention relates to the field of power system control and protection, in particular to a method that absorbs and superimposes transient energy in the PT excitation winding when a ground fault occurs in the distribution network and the circuit breaker operates differently, so as to prevent ferromagnetic resonance caused by oversaturation of the PT excitation winding The controllable harmonic elimination device of the distribution network. Background technique [0002] At present, in my country's power system, the distribution network of 35KV and below generally adopts the neutral point ungrounded method. In order to monitor the voltage of the three-phase bus to ground and the zero-sequence voltage of the system, a three-phase electromagnetic voltage transformer is installed on the bus. Due to the nonlinear excitation characteristics of the electromagnetic voltage transformer PT, when a single-phase ground fault occurs in the s...

AI Technical Summary

Problems solved by technology

During normal operation, installing a resonance eliminator at the neutral point makes the voltage measured by the PT to the ground inaccurate, which has a certain impact on the protection device of the system

When a non-metallic ground fault occurs, since the resonance eliminator will bear a large voltage, the reduction of the output voltage of the PT open delta winding may cause the zero-sequence protection to fail to operate

When a metallic ground fault occurs, the resonance eliminator is subjected to high voltage for a long time, which is easily damaged due to overheating. At the same time, the high voltage applied to both ends of the resonance eliminator causes the neutral point potential of the PT to rise sharply, threatening the insulation of the PT. It is easy to cause PT insulation breakdown and expand the scope of the accident

However, the 4PT method cannot completely eliminate the occurrence of resonance. Under certain external excitation and parameter matching, ferromagnetic resonance will still occur.

And with the expansion of the distribution network and the increase of the capacitance to the ground, the 4PT method is more likely to cause low-frequency oscillation of the system, resulting in a low-frequency saturation current with a higher amplitude

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