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 502 049-UEN A
Section 9
Glossary
131
Commissioning manual
