Progress Energy Florida installs switched shunt reactors on the 13.8 kV tertiary windings of their 500/230 kV transformer banks to reduce high system voltages during light load periods. Two 25 Mvar shunt reactors, Reactor #1 and Reactor #2 are installed on the 13.8 kV delta tertiary of the 500/230/13.8 kV autotransformer Bank #2 at the Central Florida 500 kV substation. The shunt reactors are switched with vacuum circuit breakers.

central florida substationProgress Energy Florida had an event that failed B phase winding of reactor #1 and caused collateral damage to C phase winding of reactor #1. The event also failed the tertiary 25kV center break switch #1911 and the 500/230/13.8 kV bank #2 B phase winding. It was suspected that the failure was related to excessive transient overvoltages or overcurrents resulting from reactor switching operations that could exceed the reactor insulation withstand capability and cause insulation failure.

EnerNex performed a transient study to investigate the possible cause(s) of the shunt reactor failure at their Central Florida 500 kV substation. The objective of the transient analysis was to determine the probable cause of the reactor failure and if the simulations showed excessive overvoltages. As a result of our findings, mitigating solutions were recommended.