| 摘要 |
PURPOSE:To reduce facility cost and to facilitate maintenance by realizing highly sensitive and reliable protection without installing any current differential protective relay or transmitter at non-power supply terminal. CONSTITUTION:In current differential protective relays 10, 20 comprising power supply terminals 21, 22 and a non-power supply terminal 23, protective units 10, 20 are installed only at the power supply terminals 21, 22, and basic components and second harmonic components IA2f, IB2f are detected from current information I1A-I3A, I1B-I3B at respective power supply terminals. Difference Id of basic component is then calculated for each power supply terminal, and if the difference Id is higher than a predetermined value K1, a ratio I2f/ID of second harmonic to a calculation result is calculated. If the ratio thus calculated is higher than a predetermined value K2, output from the protective relay unit is blocked, otherwise a trip command is delivered to a circuit breaker CB. This constitution prevents erroneous function of a transformer TR connected with the non-power supply terminal 23 due to excitation surge current. |
