| 摘要 |
<p>The invention provides percent unbalance or ratio ground relay (10) which detects open phase conductors on electrical distribution circuits, as well as single-phase-to-ground faults regardless of fault impedance, by providing an operating quantity (K1N1<2>|3I0|<2>) responsive to zero sequence current, and a restraining quantity (K2N2<2> |I<2>-K2N3<2> |3I0|<2>) responsive to a pre-fault balance phase current minus the zero sequence current. This restraint torque arrangement causes the relay to operate on true ratio unbalance, regardless of load. </p> |
