Tap - A connection brought out of the winding
at some point between its extremities, usually to permit changing
the voltage or current ratio.
TCC (Time Current Curve) - TCCs are a series
of points plotted in a curve on log paper describing the current-time
reacting characteristics of a current interrupting device. TCCs
are a tool used by engineers to determine coordination and correlation
Temperature Rise - The temperatures increase
over ambient due to load.
Temporary Overvoltage (TOV) - A temporary overvoltage
is define as an excursion of power frequency voltage above the
normal line-to-ground value. Such excursions are of variable magnitude
Theatre - A building, or any portion thereof,
which is used for public, dramatic, operatic, motion-picture, or
Thermal Cutout - A device affording protection
from excessive current, but not necessarily short-circuit protection,
and containing a heating element in addition to, and affecting,
a fusible member which opens the circuit.
Three Phase Power - Three separate outputs from
a single source. There is a phase difference of 120° between any
two of the three voltages and currents.
Time Current Curves (TCC) - A series of points
plotted in a curve on log paper describing the current-time reacting
characteristics of a current interrupting device; a tool used by
engineers to determine coordination and correlation of devices.
Time to Impulse Sparkover - The time between
virtual zero of the voltage impulse causing sparkover and the point
on the voltage wave at which sparkover occurs.
Tracking - Irreversible degradation of surface
material from the formation of conductive carbonized paths.
Transformer - A static electrical device which
by electromagnetic induction transfers electrical energy from one
circuit to another circuit usually with changed values of voltage
and current in the process.
Conventional - A transformer that has no protective equipment
(fuses, breakers, arresters). They are used when the protective
equipment is provided by a fuse cutout attached to the pole beside
CSP (Completely Self-Protected) - A transformer that contains
an internal breaker, an expulsion fuse and an arrester.
Dead Front - A transformer that has bushing wells and inserts
or one-piece bushings used with elbows. The operator is not exposed
to live parts.
Live Front - A transformer that has porcelain bushings with
one or two hole spades or eyebolts from primary terminations.
The operator is exposed to live parts.
Padmount - A transformer designed for mounting on a concrete
pad with underground connecting cables.
Polemount - A transformer designed for mounting on a pole with
overhead connecting lines.
Series Isolating - A transformer used in
airport series lighting circuits to maintain continuity of
the primary circuit when the continuity of the secondary circuit
Transformer Rated Meter Mounting Device - a meter mounting
device with current transformers and
with or without test switches mounted in the same enclosure.
Transient - A high amplitude, short duration
pulse superimposed on the normal voltage.
Transient Response - The ability of a circuit
to faithfully reproduce a transient applied to its input.
Turn Ratio - The ratio of the number of turns
in the high voltage winding to that in the low voltage winding.
Type I Nonmetallic Conduit - see definition for
Type II Nonmetallic Conduit - see definition