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.
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 point of transformer or generator
SVC Static VAr compensation
TC Trip coil
TCS Trip circuit supervision
TCP Transmission control protocol. The most common transport
layer protocol used on Ethernet and the Internet.
TCP/IP Transmission control protocol over Internet Protocol. The
de facto standard Ethernet protocols incorporated into
4.2BSD Unix. TCP/IP was developed by DARPA for
Internet working and encompasses both network layer and
transport layer protocols. While TCP and IP specify two
protocols at specific protocol layers, TCP/IP is often used to
refer to the entire US Department of Defense protocol suite
based upon these, including Telnet, FTP, UDP and RDP.
TEF
Time delayed earth-fault protection function
TNC connector Threaded Neill-Concelman, a threaded constant impedance
version of a BNC connector
TPZ, TPY, TPX,
TPS
Current transformer class according to IEC
UMT User management tool
Underreach A term used to describe how the relay behaves during a fault
condition. For example, a distance relay is underreaching
when the impedance presented to it is greater than the
apparent impedance to the fault applied to the balance point,
that is, the set reach. The relay does not “see” the fault but
perhaps it should have seen it. See also Overreach.
U/I-PISA
Process interface components that deliver measured voltage
and current values
UTC Coordinated Universal Time. A coordinated time scale,
maintained by the Bureau International des Poids et
Mesures (BIPM), which forms the basis of a coordinated
dissemination of standard frequencies and time signals.
UTC is derived from International Atomic Time (TAI) by
the addition of a whole number of "leap seconds" to
1MRK 502 029-UEN A Section 19
Glossary
251
Installation and commissioning manual
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