Bridge capacitor bank design and operation

The concept of a bridge capacitor bank installation was presented in a previous paper (see N.G. Andrei et. al., IEEE Trans. Power Systems, vol.8, no.4, p.1463-70, 1993). This paper discusses design and operation aspects related to the installation of a bridge capacitor bank in a substation. The 138/69 kV bridge capacitor bank installation presented by Andrei et. al. is analyzed. An automatic switching control relay scheme for the same test installation is also discussed. The control scheme takes into account the dual effect a bridge capacitor installation has upon the electrical power system: it generates reactive power on the station 138 kV bus and transfers reactive power from the 69 kV to the 138 kV bus. An unbalance protection scheme preventing the cascading type failure of the capacitor units in the 138/69 kV bridge capacitor bank is also presented. An unbalance protection scheme for high voltage, large MVAr size bridge capacitor banks is also discussed. Simple analytical formulas with practical value to evaluate the magnitude and frequency of the voltage transients generated by the energization of a bridge capacitor bank are presented. Recorded switching transient magnitudes and frequencies are compared with calculated values