Analysis Of Heating And Losses In Generator Field Discharge Resistors And Generator Rotors Following Severe Disturbances On The Electrical Supply System

ABSTRACT

The paper examines heating and losses in generator field discharge resistors and generator rotors following sustained stator-terminal and HV busbar L-L short circuits at full-load and no-load. Losses in generator rotors following L-L-L short-circuits on a weak line which is connected to the HV generator transformer busbar with clearance at fault current zeros where the generator either remains in synchronism or falls from synchronism, and following worst case malsynchronisation are also reviewed. Comparisons are made with negative sequence losses in solid generator rotors following these disturbances given by I₂ ²t computed from detailed analysis for both loaded and unloaded machines.

The analysis uses a phase-variable model of a synchronous-generator with detailed and reduced damper representations to compute stator and rotor current following a severe electrical disturbance at either the machine terminals or at the HV unit transformer busbar. Simulations at full-load and no-load for a variety of assumptions and approximations, with connection of the field discharge resistor on tripping the main generator breaker are performed. The investigations are undertaken using data for a 660MW, 3000 rpm and a 500MW, 3600 rpm Machine.