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
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, a serial master/slave protocol
for point-to-point communication
SRY Switch for CB ready condition
ST Switch or push button to trip
Starpoint Neutral/Wye point of transformer or generator
SVC Static VAr compensation
Section 9 1MRK 505 293-UUS A
Glossary
138
Commissioning manual
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