GL.19
Date Code 20090715 SEL-421 Relay
Glossary
Shunt Current—Tel ne t
Shunt Current
The current that a parallel-connected high-resistance or high-impedance
device diverts away from devices or apparatus.
SIN Operator
Operator in math SELOGIC control equations that provides the sine function.
Single-Pole Trip
A circuit breaker trip operation that occurs when one pole of the three poles of
a circuit breaker opens independently of the other poles.
SIR
Source-to-line impedance ratio.
SOTF
(Switch-Onto-Fault
Protection Logic)
Logic that provides tripping if a circuit breaker closes into a zero voltage
bolted fault, such as would happen if protective grounds remained on the line
following maintenance.
Source Impedance
The impedance of an energy source at the input terminals of a device or
network.
SQRT Operator
Math SELOGIC control equation operator that provides square root.
SSD File
IEC 61850 System Specification Description file. XML file that describes the
single-line diagram of the substation and the required logical nodes.
Stable Power Swing
A change in the electrical angle between power systems. A control action can
return the angular separation between systems to less than the critical angle.
Status Failure
A severe out-of-tolerance internal operating condition. The relay issues a
status failure message and enters a protection-disabled state.
Status Warning
Out-of-tolerance internal operating conditions that do not compromise relay
protection, yet are beyond expected limits. The relay issues a status warning
message and continues to operate.
Strong Password
A mix of valid password characters in a six-character combination that does
not spell common words in any portion of the password. Valid password
characters are numbers, upper- and lower-case alphabetic characters, “.”
(period), and “-” (hyphen).
Subnet Mask
The subnet mask divides the local node IP address into two parts, a network
number and a node address on that network. A subnet mask is four bytes of
information and is expressed in the same format as an IP address.
Subsidence Current
See CT subsidence current.
Synch Reference
A phasor the relay uses as a polarizing quantity for synchronism check
calculations.
Synchronism Check
Verification by the relay that system components operate within a preset
frequency difference and within a preset phase angle displacement between
voltages.
Synchronized Phasor
A phasor calculated from data samples using an absolute time signal as the
reference for the sampling process. The phasors from remote sites have a
defined common phase relationship. Also known as Synchrophasor.
Teln et
An Internet protocol for exchanging terminal data that connects a computer to
a network server and allows control of that server and communication with
other servers on the network.
Courtesy of NationalSwitchgear.com
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