Parallel-feeder directional overcurrent protection
US6307723A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Jun 16, 1999 |
| Grant date | Oct 23, 2001 |
| Priority date | — |
| Expiry date | Jun 16, 2019 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH02H3/081
- WIPO fieldElectrical machinery, apparatus, energy
- WIPO sectorElectrical engineering
Abstract
When directional overcurrent protection relays are included at the load end of a set of parallel feeders fed from an AC power source, a minimum fault-current threshold is specified based on the potential of a phase-to-phase fault at the source to cause a relay to operate misleadingly. This threshold is, for plain (transformerless) feeders, approximately 50% and, for transformer feeders, approximately 85% (nominally 86.7%) of rated pre-fault load current. These thresholds can, however, be ignored if the relay outputs are processed in a 2-out-of-3 circuit, so that a relay on one phase will only operate its associated circuit breaker if a relay on another phase has also operated, a condition which has been found not to obtain in the case of a source fault.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.