Capacitors at low voltage are dry-type units (i.e. are not impregnated by liquid dielectric) comprising metallised polypropylene self-healing film in the form of a two-film roll. Self-healing is a process by which the capacitor restores itself in the event of a fault in the dielectric which can happen during high overloads, voltage transients, etc.
1. Connections of capacitor banks This is the most commonly used connection mode for capacitor banks with voltages lower than 12 kV. This configuration, which is used in particular in distribution installations, provides maximum reactive power in minimum dimensions.
This is because in star connection only line-neutral voltage is applied across capacitor vs full phase-phase voltage is applied in the case of delta connection. Delta connection of capacitors requires two bushings. Since there is no connection to ground, the capacitor bank cannot be a ‘sink’ for any ground currents or zero sequence currents.
Composition of LV capacitor banks A distinction is made between fixed value capacitor banks and “step” (or automatic) capacitor banks which have an adjustment system that adapts the compensation to the variations in consumption of the installation.
High voltage capacitor banks are composed of elementary capacitors, generally connected in several serial-parallel groups, providing the required electrical characteristics for the device.
Fig. L39 – Cross-section of cables connecting medium and high power capacitor banks High-frequency voltage and current transients occur when switching a capacitor bank into service. The maximum voltage peak does not exceed (in the absence of harmonics) twice the peak value of the rated voltage when switching uncharged capacitors.