Consideration of Phase-to-Phase Surges in the Application of Capacitor Banks

The energization of capacitor banks can result in high phase-to-phase surges at locations in a power system other than the substation where the capacitor bank is being switched. The probability of obtaining high phase-to-phase surges is greater for ungrounded capacitor banks than for grounded banks. These surges are highest at a substation which is fed radially from the bus with the capacitor bank. The phlase-to-phase surges are a threat to the insulation of three-phase transformers in the radial substation. Plhase-to-ground surge arresters on the transformers are not very effective in protecting them from these surges because the surges are comprised of line-to-ground components which are approximately equal in magnitude and opposite in polarity. Therefore, the phase-to-phase surges could only be limited by arresters to two times the arrester protective level. Closing resistors in the switching device used to energize the capacitor banks are very effective in reducing the phase-to-phase surges.