Transformer iron core demagnetization method

Abstract

The invention discloses a transformer iron core demagnetization method and especially provides a method for demagnetizing the iron core of a transformer after the DC resistance test. According to the invention, the voltage is applied onto the primary winding of a transformer by a DC power supply for three times, wherein the voltage-applying amplitude is the same each time and the polarity thereof is alternately changed. The voltage-applying duration is determined based on the acquired current waveform of the primary side of the transformer. During the first two times, the current applied onto the primary winding of the transformer reaches a forward peak value and a reverse peak value respectively. During the third time, the current applied onto the primary winding of the transformer occupies only half of the duration from the forward peak value to 63.2% of the reverse peak value. Through the above three voltage application processes, the iron core of the transformer is demagnetized. Based on the above method, the demagnetization duration is greatly shortened and the demagnetization effect is ensured at the same time. Meanwhile, the demagnetization equipment is small in power and good in practicality.

Description

technical field [0001] The invention belongs to the technical field of transformer residual magnetism, and in particular relates to a transformer iron core demagnetization method. Background technique [0002] According to the requirements of the "Preventive Test Regulations for Electric Power Equipment", large transformers must be tested for DC resistance after maintenance or after 1 to 3 years of operation. The magnetic field generated by the DC current will leave a large amount of residual magnetism in the transformer core. When the transformer is switched on without load, affected by the residual magnetism of the iron core and the closing phase angle of the circuit breaker, the iron core may be saturated, resulting in a large inrush current of the transformer on the side of the sudden voltage change, resulting in a malfunction of the differential protection Tripping, causing the transformer to fail repeatedly in operation; a large value of the excitation inrush current w...

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Problems solved by technology

However, this method takes a long time to demagnetize, and it is easy to cause the hysteresis loop to shift during the process of changing the direction and size of the magnetic field, resulting in demagnetization failure, and sometimes even increases the remanence of the transformer.

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