GL.23
Date Code 20171006 Instruction Manual SEL-400 Series Relays
Glossary
TAP—Tower Footing Resistance
TAP
Tappings on some power transformer windings, used for voltage/reactive power
flow control.
TAP (Point)
Point in each phase that divides the capacitor bank into two parts.
Telnet
An IP 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.
Terminal-to-Bus-Zone
Connection Variable
SELOGIC variable stating the conditions when the relay considers the current
input from a particular terminal in the differential calculations of a particular bus-
zone.
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.
Three-Relay Application
Stations with more than 21 and as many as 54 per-phase CTs require three
SEL-487B relays. Stations with as many as 21 per-phase CTs require only one
SEL-487B.
Tie Breaker
See Bus Coupler and Bus Sectionalizer.
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 predetermined time.
Time-Domain Link (TiDL)
A technology that uses remote Axion units to provide CT and PT inputs that are
communicated to the relay by using direct fiber EtherCAT connections.
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.
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