Feasibility of thyristor controlled series capacitor for distribution substation enhancements

While thyristor controlled series capacitors (TCSCs) are already being used for control of transmission system power flows, the dynamic adjustment of transmission infeed impedances presents other system enhancement opportunities. In the case of the Con Edison system, distribution substation upgrades are severely constrained by limits to existing circuit breaker interrupting capabilities. Because additional transmission line infeeds cannot be provided without increasing fault current levels, a TCSC was investigated for use as a fault current limiter. In order to demonstrate proper operation in the current limiting mode, Electromagnetic Transients Program (EMTP) simulations were conducted. Three TCSC configurations are presented to illustrate that additional power can be provided during normal operation without increasing fault currents at the substation: (1) series compensation of existing 138 kV infeeds (to allow higher substation MVA uprates); (2) series compensation of new 138 kV infeeds (without fault current increases); and (3) a 13.8 kV TCSC compensated link between two substations (to allow regulated power transfer between substation buses)