PHASE SELECTION FOR SINGLE-POLE TRIPPING ―WEAK INFEED CONDITIONS AND CROSS-COUNTRY FAULTS

摘要

The issues of cross-country faults and weak infeed conditions have been discussed in conjunction with phase selection and single-pole tripping/autoreclosing functions. A new phase selection algorithm has been presented that uses a proven principle enhanced by the novel usage of voltage signals and adaptive techniques. The idea of 'self-monitoring' has been applied to the phase selector. The algorithm sets the VOID flag in uncertain situations instead of providing wrong information. The uncertain situations for the applied algorithm are likely to be resolved by distance elements. Such hierarchical combination of the phase selector and the distance elements provides much better performance. The phase selector can work using currents only, currents and line-to-line voltages, or currents and full set of voltages. The phase selector is fast and operates typically between 1/4 and 1/2 of a power cycle. The issue of single-pole tripping initiated by pilot schemes during cross-country faults has been discussed. A solution is presented which uses two channels to improve the performance in the single-pole tripping mode.