Protection system for undetected over voltage in an isolated voltage regulator

A protection circuit for use in an electric power generating system having a three phase wye wound generator coupled through a generator control breaker to a load bus, the generator producing a three phase balanced ac electrical output, the magnitude of which is controlled by a voltage regulator utilizing isolated voltage and current sensing feedback for each phase, comprising:

• first means for monitoring the magnitude of each phase of the isolated voltage sense feedback, said first means generating a first output control signal for each phase if the magnitude of said phase is below a first predetermined threshold;
• second means for monitoring the magnitude of each phase of the isolated current sense feedback, said second means generating a second output control signal for each phase if the magnitude of said phase is below a second predetermined threshold;
• first logical AND means coupled to said first means and said second means for generating a phase fault sensed signal for each phase when said first output control signal and said second output control signal are both generated for a particular phase;
• logical OR means for generating a fault sensed signal when any of said phase fault sensed signals are generated;
• second logical AND means for generating a protective trip signal when said fault sensed signal is generated and when no phase is open and when the generator control breaker is closed;
• and
• time delay means for delaying said protective trip signal for a predetermined period of time after said fault sensed signal has been generated and when no phase is open and when the generator control breaker is closed, said protective trip signal thereafter de-exciting the generator and opening the generator control breaker.