Modern Stability Aids for Calvert Cliffs Units

Stability is difficult to maintain under the three- phase-fault-breaker-failure criterion with a plant of two nominal 800 MW units connected radially by two 500 kV lines to a 230 kV load network. This paper describes the application of dynamic stability aids such as: fast-valving, 500 kV breakers with independently operated poles, fast-excitation, and alternate 500 kV line arrangements, and investigates machine internal losses during the fault, alternative fault types and locations, and the setting of the load unbalance relays. The costs of the alternative stability aids are compared and a choice of load unbalance relay settings for initiating fast-valving is made to obtain stability at a minimum cost with fast-valving and 500 kV breakers having independently operated poles.