A Capacitor Bank Simulation Model

Power system capacitor banks form critical components of reactive power support and filtering arrangements in high voltage direct current converter stations, such as those connecting electrical power networks with interconnectors, and with offshore wind resources which promise abundant renewable energy but are necessarily distant from centres of demand. Capacitor banks are typically configured in balanced arrangements, where standards require each unit to be measured individually at commissioning and positioned to best balance a neutral or bridge. Capacitor bank rack voltages are tiered but are shared among all units on each rack, which can test dielectrics: this paper presents simulation models to explore distributions of dielectric stress which can result from such arrangements. On a symmetrical rack configured with series-connected units, preliminary results suggest voltages (and therefore electric field stresses) are not evenly shared throughout units in the bank, as: each unit has its own uneven voltage distribution; and rack voltages common to all supported units subject those furthest from a rack tie connection to greater stress than those positioned centrally. Where dielectrics throughout a bank are similar, disproportionate stresses suggest incipient faults and eventual insulation breakdown are more probable for certain unit positions, such as corner units and those at higher voltage. An improved understanding of how unit position affects failure probability could help detect faults, corroborate failure locations detected with reactance techniques, or otherwise direct initial searches for degraded units.