Vibration analysis of power capcitors and vibration reduction with damping structures

Abstract

Vibration of AC filter capacitor generates loud noises in HVDC converter stations, which would reach 105dB. Currently, vibration features are not investigated thoroughly. The objective of this work was to measure vibration velocity distribution on AC filter capacitor surfaces and to investigate the vibration features. In the experiments, the capacitor was applied currents consist of three components of 50 Hz, 550 Hz and 650 Hz. The root mean squared values were 30 A, 25 A and 4.6 A, respectively. A portable digital vibrometer was conducted to measure the vibration velocity on capacitor surfaces. In order to obtain velocity data simultaneously, voltage squared was used as a datum signal to calibrate the time offset. It was found that velocities on different measure points on a capacitor surface were not synchronous, and had different phases. On the bottom surface, vibrations performed entirely transverse oscillating. On the broad side surfaces, there were two bending wave generated from the edges connected to bottom and top surfaces. It was concluded that the internal vibration of elements excited firstly on the bottom surface, and then through the edges of bottom and broad side surface, it transmitted on broad side surfaces. A damping structure was designed and applied on the bottom surface to increase the damping coefficient between contact surfaces and to reduce vibration transmitted to broad side surfaces. The sound measurement result shown that the damp-structure capacitor had sound power which was 73.3% of that generated from the conventional capacitor.