| 摘要 |
PURPOSE:To detect surely a one-phase ground-fault accident even when a system is operated with a low frequency by controlling the set value of a protective relay through a physical quantity detector which detects a physical quantity proportional to the frequency of a power system. CONSTITUTION:The output from a variable voltage and variable frequency power supply device 2 is impressed to an AC motor 4 of a load of the power system through an output transformer 3. A pilot generator 7 is interlocked by this motor 4 to detect a physical quantity proportional to the frequency of the power system, and a sensitivity set value, which is proportional to the system frequency, of the protective relay 8 is controlled and changed in accordance with this detection output. Consequently, a zero-phase detection voltage from an open tertiary winding 31 of the transformer 3 whose output is changed in accordance with the frequency becomes the set value or higher even for the ground-fault at a point F of the power system when the motor 4 is driven with a low frequency, and the one-phase ground-fault accident is detected surely through the relay 8.
|
