OLTC On-load tap changer
OTEV Disturbance data recording initiated by other event than
start/pick-up
OV Over-voltage
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
PCM600 Protection and control IED manager
PC-MIP Mezzanine card standard
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
PSM Power supply module
PST Parameter setting tool within PCM600
PT ratio Potential transformer or voltage transformer ratio
PUTT Permissive underreach transfer trip
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
SCL Short circuit location
SCS Station control system
SCADA Supervision, control and data acquisition
SCT System configuration tool according to standard IEC 61850
SDU Service data unit
1MRK 505 291-UEN A Section 17
Glossary
329
Application manual
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