Apparatus and method for protecting synchronous generators against off-nominal frequency deviation and alternating forces excitation

A method for operating a synchronous generator, the method comprising:

• providing a relay system adapted to respond to an electrical signal representative of an actual frequency at which the generator is operating and to an electrical signal representative of an actual forcing amount at which the generator is operating;
• providing a desired off-nominal frequency range, a desired lower forcing amount, and a desired upper forcing amount;
• measuring an actual frequency at which the generator is operating, and measuring an actual forcing amount at which the generator is operating;
• comparing the actual frequency with the off-nominal frequency range, and comparing the actual forcing amount with the lower and/or upper forcing amounts;
• and
• selectively alarming the operator or tripping the generator to an off-line mode based upon the frequency comparison and the forcing comparison.

A synchronous generator, comprising:

• an axially extending rotor enclosed in an annular stator that surrounds and sleeves the rotor;
• a frequency source signal in operative association with the rotor and stator representative of an actual frequency at which the generator is operating;
• a forcing source signal in operative association with the rotor and stator representative of an actual forcing amount at which the generator is operating;
• and
• a relay system adapted to respond to the frequency source signal and the forcing source signal by comparing the actual frequency with a predetermined desired frequency range and comparing the actual forcing amount with at least one predetermined maximum forcing amount, and selectively alarming the operator or tripping the generator to an off-line mode depending upon the comparisons.