DISTRIBUTION LINE DISCONNECTION DETECTION APPARATUS FOR THREE-PHASE CIRCUIT

PURPOSE:To enable extremely certain detection of disconnection by reducing the effect of load variation at the time of disconnection, by respectively detecting change components of the positive-phase-sequence current and negative-phase-sequence current of a three-phase circuit and operating the same according to a specific formula. CONSTITUTION:The title apparatus is constituted of a fundamental wave filter 5, filters 6, 7 for detecting a positive-phase-sequence component and a negative-phase-sequence component, detection circuits 8, 9 for detecting a positive-phase-sequence change component and a negative- phase-sequence change component and a level judge circuit 10 for detecting the level of each change component. The phase currents Ia, Ib, Ic (all of which are a complex quantity) flowed to a distribution line 2 are applied to a fundamental wave filter 5 through a current transformer 3 and an auxiliary current transformer 4 and only fundamental waves are taken out. The positive-phase-sequence component I1 and the negative-phase-sequence component I2 are detected by the filters 6, 7 and the differences I1, I2 between the positive-phase-sequence current and the negative-phase-sequence current at the time of normality, and the positive-phase- sequence component I1 and the negative-phase-sequence component I2 from the filters 6, 7 are outputted from the circuits 8, 9. Hereupon, the operation of Qx=(DELTAI2/DELTAI1)(¦DELTAIx¦/2¦DELTAI2 ¦) (where in x=a,b,c) is performed by an operation circuit 12 and the operation result is compared with the setting region of a setting part 14 by a comparator circuit 13 to output a disconnection alarm.