Ultra fast distance protection

The chief advantage that the distance relay has over current-only based line protection schemes is its ability to provide a defined zone of protection without the need for a communications channel a so-called direct tripping, under-reaching zone. This zone must operate for faults within its zone of coverage with no appreciable time delay and restrain itself for all faults beyond its reach. It must do this in the presence of complicating factors such as fault resistance, circuit loading, switching transients, power swings, and instrument transformer errors. This paper focuses on the internal mechanisms and external influences that affect the speed of operation of the under-reaching zone of the distance relay. It presents a new approach that achieves sub-cycle performance for a broad range of conditions. The present paper details why it´s difficult for a distance relay to be fast. The relay shall respond to relatively small changes in voltage and current. In order to do so the relay must extract phasor components from the waveform. Shortening the window for phasor estimation risks responding to non-fundamental components (errors). If there were no errors in the waveform then this would not be an issue. However the natural response of both the power system and the instrument transformers do produce significant errors. A variety of approaches have been taken to improve performance. A time domain implementation is presented that promises to provide faster operating time. This approach allows filtering to be delayed until later in the process. As well a filter is presented that effectively removes the transient component of the CVT. The proposed algorithm takes the form of an accelerator, which is logically ORed with a more conventional, frequency domain (phasor-based) algorithm. Carrying out calculations in the time domain