MAGNIFICATION OF TRANSIENT VOLTAGES IN MULTI-VOLTAGE-LEVEL, SHUNT-CAPACITOR-COMPENSATED, CIRCUITS

To increase the capacity of existing facilities it has become an increasingly prevalent practice for utilities and industrial plants to install shunt capacitors in their power systems for voltage support and power factor correction. Switching of these capacitor banks produce transients, and as additional shunt capacitor banks are installed, the per unit transient voltages can be increased. "Magnification" of switching surges in a power system with shunt capacitors at two voltage levels has been reported in References [1] and [2]. In these reports it was found that, when two series connected L-C loops approach the same natural frequency, the transient voltages are amplified more and more. Many of the present-day power systems have shunt compensation at two or more voltage levels. Further study into the performance of these systems during capacitor switching is warranted to ensure that transient voltages do not reach levels where equipment damage may occur. This paper examines the transient response of two, three and four series L-C loop systems, and presents the results of a case study of voltage magnification on an actual system with shunt capacitors at four different voltage levels. On this system, equipment damage occurred within an industrial plant in the same time frame of the energization of a capacitor bank in a utility substation.[3] Curves which illustrate the theoretical maximum components of the transient overvoltages and their interaction with the 60 Hertz fundamental voltage in actual systems are presented.