NCC National Control Centre
OCO cycle Open-close-open cycle
OCP Overcurrent protection
OLTC On load tap changer
OV Over voltage
Overreach A term used to describe how the relay behaves during a fault
condition. For example a distance relay is over-reaching when
the impedance presented to it is smaller than the apparent
impedance to the fault applied to the balance point, i.e. the set
reach. The relay “sees” the fault but perhaps it should not have
seen it.
PCI Peripheral component interconnect, a local data bus
PCM Pulse code modulation
PCM600 Protection and control IED manager
PC-MIP Mezzanine card standard
PISA Process interface for sensors & actuators
PMC PCI Mezzanine card
POTT Permissive overreach transfer trip
Process bus Bus or LAN used at the process level, that is, in near proximity
to the measured and/or controlled components
PSM Power supply module
PST Parameter setting tool within PCM600
PT ratio Potential transformer or voltage transformer ratio
PUTT Permissive underreach transfer trip
RASC Synchrocheck relay, COMBIFLEX
RCA Relay characteristic angle
REVAL Evaluation software
RFPP Resistance for phase-to-phase faults
Resistance for phase-to-ground faults
RISC Reduced instruction set computer
RMS value Root mean square value
RS422 A balanced serial interface for the transmission of digital data in
point-to-point connections
RS485 Serial link according to EIA standard RS485
1MRK506276-UUS B Section 15
Glossary
109
Operator's manual
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