NCC National Control Centre
NOF Number of grid faults
NUM Numerical module
OCO cycle Open-close-open cycle
OCP Overcurrent protection
OEM Optical Ethernet module
OLTC On-load tap changer
OTEV Disturbance data recording initiated by other event than start/pick-up
OV Overvoltage
Overreach A term used to describe how the relay behaves during a fault condition.
For example, a distance relay is overreaching when the impedance
presented to it is smaller than the apparent impedance to the fault
applied to the balance point, that is, 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
PELV circuit Protected Extra-Low Voltage circuit type according to IEC60255-27
PMC PCI Mezzanine card
POR Permissive overreach
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
PRP Parallel redundancy protocol
PSM Power supply module
PST Parameter setting tool within PCM600
PTP Precision time protocol
PT ratio Potential transformer or voltage transformer ratio
PUTT Permissive underreach transfer trip
RASC Synchrocheck relay, COMBIFLEX
RCA Relay characteristic angle
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
RTC Real-time clock
RTU Remote terminal unit
SA Substation Automation
SBO Select-before-operate
SC Switch or push button to close
1MRK 505 370-UEN D Section 22
Glossary
Busbar protection REB670 465
Application manual
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