Common use of Unload Clause in Contracts

Unload. Auto unload is a protective measure which is activated on high blade path temperature spread or high average temperature. Control action will reduce load until the fault condition clears. If minimum load is reached, the generator breaker is opened and the turbine held at synchronous speed for cool down and then tripped. This condition is annunciated to the operator and cannot be defeated. o Switchyard Breaker Trip. Switchyard breaker trip results from generator faults which are recoverable such as reverse power, voltage regulator trips, voltage balance functions. Control action is to open the generator breaker and hold the turbine at synchronous speed. Control action is annunciated. o Fast shutdown/load dump. These control actions both trip the switchyard breaker immediately and also shut down the turbine. They differ only in the length of time between opening the breaker and turbine trip. These actions are taken based on both generator faults such as ground faults and turbine faults such as very high blade path temperature spread or severe over/under speed with the breaker closed. -------------------------------------------------------------------------------- Proprietary Information Page 13 AES IRONWOOD CONTRACT FINAL ISSUE - OCTOBER 30, 1998 --------------------------------------------------------------------------------