LED
Light emitting diode
LNT
LON network tool
LON
Local operating network
MCB
Miniature circuit breaker
MCM
Mezzanine carrier module
MIM
Milli-ampere module
MPM
Main processing module
MVB
Multifunction vehicle bus. Standardized serial bus originally
developed for use in trains.
NCC
National Control Centre
NUM
Numerical module
OCO cycle
Open-close-open cycle
OCP
Overcurrent protection
OEM
Optical ethernet module
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
PCM 600
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
PT ratio
Potential transformer or voltage transformer ratio
PUTT
Permissive underreach transfer trip
RASC
Synchrocheck relay, COMBIFLEX
Section 15
Glossary
RET 670
Operator's manual
1MRK504049-UEN rev. D
89