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
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
SELV circuit Safety Extra-Low Voltage circuit type according to IEC60255-27
SFP Small form-factor pluggable (abbreviation)
Optical Ethernet port (explanation)
SLM Serial communication module.
SMA connector Subminiature version A, A threaded connector with constant impedance.
SMT Signal matrix tool within PCM600
SMS Station monitoring system
SNTP Simple network time protocol – is used to synchronize computer clocks on local
area networks. This reduces the requirement to have accurate hardware clocks
in every embedded system in a network. Each embedded node can instead
synchronize with a remote clock, providing the required accuracy.
SOF Status of fault
SPA Strömberg Protection Acquisition (SPA), a serial master/slave protocol for point-
to-point and ring communication.
Section 16 1MRK 504 165-UUS Rev. J
Glossary
320 Transformer protection RET670
Commissioning manual
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