Load Rejection Operation in Conventional Power Plants in Enel-Italy

The capability of maintaining auxiliary load after a main breaker trip following an emergency in the electric power system is of major concern for any thermoelectric generating unit. In ENEL the reliability of run back to house load of fossil fired units has been greatly improved by adopting a new procedure. Instead of that originally recommended the new procedure allows to trip all fuel input to the boiler and maintains house load operating the turbine on mass and energy stored in the boiler. This procedure was qualified a few years ago and since then is used in the 320 MW units in operation (the main bulk of ENEL´s thermal capacity) whether equipped with subcritical once through boilers or with assisted circulation drum boilers. A series of tests carried out recently on supercritical 660 MW units have shown that adopting the same procedure these large units can sustain successfully the runback to house load too. Up to now the new procedure has been used in many other thermal units of size ranging between 70 MW to 240 MW and can be performed in most of ENEL´s thermal power plants.