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 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
PISA
Process interface for sensors & actuators
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
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
RFPP
Resistance for phase-to-phase faults
RFPE
Resistance for phase-to-earth 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
RTC
Real-time clock
RTU
Remote terminal unit
SA
Substation Automation
SBO
Select-before-operate
SC
Switch or push button to close
SCS
Station control system
SCADA
Supervision, control and data acquisition
SCT
System configuration tool according to standard IEC 61850
SDU
Service data unit
SMA connector
Subminiature version A, A threaded connector with constant
impedance.
Section 11
1MRK 514 014-UEN A
Glossary
54
650 series
Installation manual
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