Identification of three phase trip with ACT DO
TR IEC 61850-7-500
In IEC 61850-7-3 ed2.1 Table 21, the use of DA « general” of cdc ACT is specified. It can be used as general (three phase) trip, but table 21 requires also “general” to be set if the protection function only emits a trip command for one phase. This requirement poses a problem for the following use cases:
1. For circuit breaker featuring single phase trip capacity, there is one trip contact for each phase and a three-phase trip contact. The association of the three-phase trip contact is logical and can be considered as redundancy. This association is impossible if general is to be set for single-phase command.
2. The recloser automaton requires information whether a trip was single phase (and on which phase) or three phase. For single phase trips, DA phs* can be used. It would be logical to use DA “general” for three phase trip indication. This is impossible if general is to be set for single-phase command, as each single-phase trip would wrongly initiate a three phase cycle.
Conclusion: a DA indicating three phase trip, independent from single-phase-trip is necessary.
Proposal: accept “general” to indicate three phase trip independent from single phase trip. For this, delete the last part of the value description for “general”: “'general' shall be set if one of the 'phsX'/'neut' is set”. This would allow the application to decide (as it should be), enabling the aforementioned use cases.
- a specific DA for three phase trip (phsABC ?) could be introduced, but this would have a very huge impact and should probably be avoided.
- the combined use of phsA, phsB and phsC to indicate a three phase trip would require an additional logic gate for the circuit breaker interface connected to circuit breakers without three phase capability and having only one trip contact. This would delay the overall trip time and is not desirable.
- Different implementation in protection functions depending on whether they are associated to cb with single and three phase capability or three phase capability only. This would cause many implementation issues for the protection functions and seems not acceptable.