How to Measure and Analyze the Vibration and Noise of 500kV Power Transformer Caused by DC Magnetic Bias

Abstract: The on-line synchronous monitoring scheme on 500kV single-phase power transformer is designed in the paper. With the application of vibration and noise sensor, data acquisition and analysis system, single-phase power transformer in 500kV substation is monitored real-time under the DC magnetic bias condition. The vibration and noise time-domain waveform data before and after DC bias are recorded, and spectrum range of vibration and noise signal are analyzed. Test results show that vibration and noise amplitude of power transformer under the influence of DC bias increase obviously, and large quantities of high harmonic appear, which is not helpful for normal operation of transformer. 

Key words:  Transformer vibration, noise, DC magnetic bias, on-line monitoring, spectrum    

Introduction

With the formation of AC-DC hybrid transmission mode, mutual interference of AC and DC system also comes. When the DC line adopts mono-pole operation mode, the DC current, which flows into the ground through grounding electrode, will have an influence on electric equipment in the AC electric system. Under the mono-pole operation mode, some transformers vibrates more violently, and the noise becomes louder. The comparison between noise and debug load indicates that there is close link between them. Large quantities of similar test data prove that DC magnetic bias is the main cause for vibration and noise intensification. When DC bias occurs, internal leakage flux greatly increases in terms of amplitude, and plenty of high harmonics also appear. Hence, the vibration of windings and silicon steel sheets intensifies. The vibration transmits to box surface through insulation oil and iron foot pad. The amplitude and harmonic increase as well.