Capacitor failure analysis

An industrial plant was experiencing unexplained capacitor failures and fuse operations in an automatically switched capacitor bank. Simply replacing the blown fuses did not solve the problem so a detailed examination was conducted. Failures were attributed to capacitor energization transients. However, occassional chattering of 50-kvar steps in the capacitor banks were observed. The contactors were replaced once it was determined that the energization transients were most likely due to the chattering contactors. However, problems still persisted prompting electricians to conduct another investigation. They reported that when variable step 2 was brought online with variable step 1 already online, the contactor for step 1 would drop out and pick up the contactor to eight times within one minute thus exposing the capacitor to many switching transients. The next step was to replace the control board in the capacitor bank whcih monitored the power factor and determined which steps to breing online. Since a new board was ordered and installed there have been no capacitor failures or fuse operations in the bank, confirming that the control board was the problem.