| 摘要 |
PURPOSE:To detect surely a one-phase ground-fault accident even when a system is operated with a low frequency by providing a physical quantity detector which detects a physical quantity proportional to the frequency of the system and varying the set value of a protective relay device in accordance with the output of this detector. CONSTITUTION:Since a voltage es outputted from a pilot generator 8 is inputted to an overcurrent relay 93 through an input device 92 and is increased or reduced in proportion to the frequency of the system, the set value of the relay 93 is not fixed but is varied to alphaXkf in response to the frequency. Consequently, if a one-phase ground-fault accident occurs, the relay 93 compares the detection input proportional to the frequency with the set value proportional to the frequency (f) of the system at the one-phase ground-fault accident time. In case that the sensitivity is so set that detection is possible up to 40 % incomplete ground-fault when the frequency (f) of the system is a commercial frequency fs, the set value is reduced to 40% when the frequency (f) is reduced to 40% and therefore, a detection signal can be outputted. Thus, the one-phase ground- fault is detected even in the operation with a low frequency to enhance the reliability of the system protection.
|
