Supervisory circuit for generator cyclic loads - measuring rate of load change and initiating trip if rate and frequency are above set limits

摘要

The application of the proposed circuit is principally to generators which can be subjected to cyclic loads of a magnitude lower than that detectable by normal protection circuits. Generators connected to an HVDC transmission system can be subjected to such loads. A wattmetric transducer (2) connected to the generator output passes signals to two asymmetrical level detectors (3,4), one being the opposite of the other. The level detectors drive integrators (5,6) with feedback to the detector input. These two channels follow load increase (5,AB) and load decrease (6,AUF) respectively. If the proportion of change to actual power (7,8) exceeds a limiting value (9,10) a bistable circuit (11) is tripped, and its output applied to a counter (Z). This initiates a trip (AS) after a set number of impulses in a time given by a monostable (13). With the circuit dangerous power oscillations can be detected and the machine unloaded when the magnitude of the change is within the normal overload protection limits.