Switching of Medium Voltage Capacitor Banks and the Impact of Overvoltages on the Components of an Electrical System

Abstract

The study aimed to determine the regularities of switching overvoltages during the operation of medium-voltage capacitor banks and to evaluate the effectiveness of methods for their reduction. The methodology was based on a combination of mathematical modelling in specialised environments, laboratory testing of condenser plant models and statistical analysis of operational data. The results showed that the amplitude of overvoltages in capacitor banks increased from 1.6-2.0 to 2.5-3.0 relative units depending on the power, and the duration of transients exceeded 2.8 milliseconds at large capacities, which created a risk of insulation damage. The study determined that more than 90% of capacitor failures were of an insulating nature, with daily switching reducing service life by a third, and overvoltage over 2.5 relative units halving service life. The study showed that in the secondary circuits of transformers during resonant interaction, the amplitude of overvoltages reached 4.0-4.5 relative units, which led to the failure of electronic devices and premature tripping of protections. The effectiveness of the technical equipment confirmed that synchronous circuit breakers reduced the level of overvoltage to 1.2 relative units, while pre-trigger resistors and overvoltage limiters reduced it by 40-50%, but required frequent maintenance. The conclusions of the study were to substantiate the need for the integrated use of protection methods that ensure both technical reliability and economic feasibility of operation, and the results obtained can be used by power engineers and design organisations to optimise operating modes and increase equipment durability.