GL.20
SEL-421 Relay Date Code 20111215
Glossary
Terminal Emulation Software—Unbuffered Report
Terminal
Emulation Software
Software that can be used to send and receive ASCII text messages and files
via a computer serial port.
Thermal Demand
Thermal demand is a continuous exponentially increasing or decreasing
accumulation of metered quantities; used in demand metering.
Thermal
Withstand Capability
The capability of equipment to withstand a predetermined temperature value
for a specified time.
Three-Phase Fault
A fault involving all three phases of a three-phase power system.
Three-Pole Trip
A circuit breaker operation that occurs when the circuit breaker opens all three
poles at the same time.
Time Delay on Pickup
The time interval between initiation of a signal at one point and detection of
the same signal at another point.
Time Dial
A control that governs the time scale of the time-overcurrent characteristic of
a relay. Use the time-dial setting to vary relay operating time.
Time-Delayed Tripping
Tripping that occurs after expiration of a pre-determined time.
Time Error
A measurement of how much time an ac powered clock would be ahead or
behind a reference clock, as determined from system frequency
measurements.
Time-Overcurrent
Element
An element that operates according to an inverse relationship between input
current and time, with higher current causing faster relay operation.
Time Quality
An indication from a GPS clock receiver that specifies the maximum error in
the time information. Defined in IEEE C37.118.
Torque Control
A method of using one relay element to supervise the operation of another.
Total Clearing Time
The time interval from the beginning of a fault condition to final interruption
of the circuit.
Tower Footing Resistance
The resistance between true ground and the grounding system of a tower.
Transformer Impedance
The resistive and reactive parameters of a transformer looking in to the
transformer primary or secondary windings. Use industry accepted open-
circuit and short-circuit tests to determine these transformer equivalent circuit
parameters.
Tree Resistance
Resistance resulting from a tree in contact with a power line.
TVE
Total Vector Error. A measurement of accuracy for phasor quantities that
combines magnitude and angle errors into one quantity. Defined in IEEE
C37.118.
TXD
Transmitted data.
UCA2
Utility Communications Architecture. A network-independent protocol suite
that serves as an interface for individual intelligent electronic devices.
Unbalanced Fault
All faults that do not include all three phases of a system.
Unbuffered Report
IEC 61850 IEDs can issue immediate unbuffered reports of internal events
(caused by trigger options data-change, quality-change, and data-update) on a
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