Operational performance of generator condition monitors: comparison of heated and unheated ion chambers

Generator condition monitors (GCMs) are evaluated under field conditions in a 550 MW turbogenerator. Small 100 W resistors coated with insulating paints and varnishes are mounted inside the generator to simulate overheating. The GCM responds very rapidly to an overheating event, typically within two minutes, even for hot spots as small as 10 cm². Similarly, the aerosols produced on overheating are extremely short-lived, decaying within two to three minutes after overheating is discontinued. Use of heated ion chambers is found to desensitize the GCM regardless of the nature of the overheated insulation and in some cases prevents the GCM from reaching the 50% preset alarm level commonly used on GCMs. Use of heated ion chambers is therefore generally not recommended except where severe oil mist problems may exist