Temporary Rental Spot Mobil Portable Transfer Switches, Transformers and Power Conditioners
A transformer which uses air as the
cooling method medium. Term is
abbreviated with the ANSI designation
AA indicating open, natural draft ventilated
Ambient Noise Level
The inherent or existing noise level
of the surrounding area measured
The inherent or existing temperature
of surrounding atmosphere into which
the heat of a transformer is dissipated.
Transformers are designed for 30°C
average ambient temperature with
a 40° C maximum during any 24
A unit of electric current flow.
American National Standards Institute,
Inc.– a recognized organization which
specifies the standards for transformers.
American Society for Testing Materials.
Air Terminal Chamber. See Terminal
A term used to denote a decrease in
magnitude in transmission from one
point to another. Typically expressed as
a ratio or in decibels, as in electrical
A transformer with one winding per
phase in which part of the winding is
common to both the primary and the
Two or more single phase transformers
connected together to supply a three
Basic Impulse Level measures the ability
of the insulation system to withstand
high voltage surges.
Small KVA, two-winding transformers
typically wired as an autotransformer
to raise or lower single and three phase
line voltages by 10 - 20%.
Cast Coil Transformer
Transformer with coils solidly case in
epoxy resin under vacuum in a mold.
Also called cast resin or epoxy cast coil
A reduced capacity tap at the midpoint
in a winding. Also referred to
as lighting tap.
Actual values taken during production
testing which certify the values or
results or testing to apply to a specific
Turns of electrical grade wire or strip
conductor material wound on a form;
often referred to as winding.
Electrical noise or voltage disturbance
that occurs between one of the line
leads and the common ground, or
between the ground plane and either
the line or the neutral.
A transformer with a turns ratio which
provides a higher than rated voltage at
no load and rated voltage at rated load.
Such transformers cannot be used for
Losses in watts caused by the resistance
of the transformer winding during
a loaded condition. Also referred to as
load loss or winding loss.
The constant load which a transformer
can maintain indefinitely, at rated voltage
and frequency, without exceeding
its designed temperature rise.
A transformer designed to provide good
voltage regulation for control or instrumentation
circuits having high inrush
current or low power factor conditions.
See load loss.
Electrical grade steel laminations which
carries the magnetic flux.
Losses in watts caused by magnetization
of the core and its resistance
to magnetic flux when excited or
energized at rated voltage and
frequency. Also referred to as
excitation loss or no-load loss.
Transformer generally used in control
or instrumentation circuits for measuring
A standard unit of measure of intensity.
A standard three phase connection
with the ends of each phase winding
connected in series to form a loop with
each phase 120 degrees from each
other. Also referred to as 3-wire.
A term or symbol indicating the primary
connected in delta and the secondary
in wye when pertaining to a three
phase transformer or transformer bank.
A series of tests conducted to verify
effectiveness of insulation materials
and clearances used between turns
and layers in the winding.
Generally referred to as any transformer
rated 500 KVA and below, except for
current, potential, or other specialty
A transformer without liquid for cooling.
A winding consisting of two separate
parts which can be connected in series
or in parallel. Also referred to as dual
voltage or series multiple winding.
Conductor material placed between the
primary and secondary windings which
is grounded to reduce electrical noise or
“No-load current” flowing in the
winding used to excite the transformer
when all other windings are open--
circuited. Usually expressed in percent
of the rated current of a winding in
which it is measured.
Transformer with coils either encased
or cast in an epoxy resin or other encapsulating
“Full Capacity Above Normal.” A
designation for no-load taps indicating
the taps are suitable for full-rated KVA
at the designated voltages above
Same as above except Full Capacity
Cooled mechanically to maintain rated
temperature rise, typically using auxiliary
fans to accelerate heat dissipation.
A non-rigid connection used to eliminate
transmission of noise and vibration.
Designates the number of times, or
complete cycles, that polarity alternates
from positive to negative per unit of
time; as in 60 cycles per second. Also
referred to as Hertz.
Full Capacity Tap
Tap than can deliver rated KVA without
exceeding its designated temperature
A special 3 phase autotransformer used
to establish a stable neutral point on a
3-wire delta system. Also referred to as
Connecting one side of a circuit to
earth; or creating a conducting path to
some conducting body that serves in
place of earth through low-resistance or
A term for AC frequency in cycles
High Voltage Winding
Designates the winding with the
greater voltage; designated as HV on
the nameplate and as H1, H2, etc. on
High potential dielectric test impressed
on the windings to check insulation
materials and clearances.
Dielectric test which determines BIL
capability by applying high frequency,
steep wave-front voltage between
windings and ground.
Retarding or opposing forces of
current flow in AC circuit, expressed
Induced Potential Test
A high frequency dielectric test which
verifies the integrity of insulating
materials and electrical clearances
between turns and layers of a winding.
A property which opposes a change in
Abnormally high current, caused by
residual flux in the core, which is
occasionally drawn when a transformer
One which the primary winding
connected to the input or source, is
insulated from the secondary winding
connected to the output or load. Also
referred to as two-winding or isolation
transformers, which isolate the primary
circuit from the secondary circuit.
See No Load Loss or Core loss.
Percent resistance. Voltage drop due
to conductor resistance at rated current
expressed in percent of rated voltage
Percent reactance. Voltage drop due to
reactance at rated current expressed in
percent of rated voltage.
Percent impedance. Voltage drop
due to impedance at rated current
expressed in percent of rated voltage.
Kilovolt ampere rating with designates
the capacity or output with a transformer
can deliver at rated voltage and
frequency without exceeding designed
temperature rise. (1 KVA = 1000VA, or
1000 volt amperes).
Thin sheets of special steel used to
make the core of a transformer.
A transformer which used mineral oil,
or other dielectric fluid, which serves
as an insulating and cooling medium.
Losses in watts which are the result
of current flowing to the load. Also
referred to as winding loss, copper loss,
or conductor loss.
A reduced capacity tap midway in a
winding. Also referred to a Center tap;
usually in the secondary winding.
National Electric Code.
National Electrical Manufacturers
See core loss.
A transformer which uses oil as the
cooling medium. Term is abbreviated
with the ANSI designation OA indicating
natural oil ambient ventilation.
Transformers having compatible design
features with their appropriate terminals
Classification of an AC circuit; typically
designated as single phase 2-wire or
3-wire, or three phase 3-wire or 4-wire.
Designates the instantaneous direction
of the voltages in the primary compared
to the secondary.
A transformer generally used in instrumentation circuits for measuring or
The relation of watts to volt amps in
The input, source, or supply side
connected to the primary of the
transformer in a circuit.
The design characteristics, such
as primary and secondary voltage,
KVA, capacity, temperature rise,
Refers to the turns ratio or the voltage
ratio between the primary and secondary
The effect of inductive and capacitive
components of a AC circuit producing
other than unity power factor.
A single winding device with an air or
iron core which produces a specific
amount of inductive reactance into a
circuit, usually to reduce or control
Reduced Capacity Taps
Taps which are rated for winding
current only (versus rated KVA), thus
reducing available power because of
lower output voltage.
The percent change in secondary output
voltage when the load changes from full
load to no-load at a given power factor.
A transformer connection generally
used to get a two phase output from
the secondary of a three phase input,
or vice versa.
An enclosed transformer completely
sealed from the outside environment
and usually contains pressurized
The output, or load side connected
to the secondary of the transformer
in a circuit.
A winding consisting of two or more
sections which can be connected for
series operation or multiple (parallel)
operation. Also referred to as dual
voltage or series-parallel.
Same as wye connection.
One in which the energy transfer is
from the high voltage winding (primary
input circuit) to the low voltage winding
(secondary output or load circuit).
The energy transfer is from the low
voltage winding to the high voltage
winding; with the low voltage winding
connected to the power source (primary
input circuit) and the high voltage
connected to the load (secondary output
Use of Scott connection for three phase
operation using two primary (main) and
two secondary (teaser) coils.
A connection brought out of winding
at some point between its extremities
to permit changing the nominal voltage
ratio. Taps are usually located in the
high voltage winding, typically expressed
as FCAN and FCBN for no-load
The increase over ambient temperature
of the winding due to energizing and
loading the transformer; typically
measured as either average rise by
resistance or as hot-spot.
An enclosure with space for making
connection to a substation transformer,
typically used when the transformer is
not direct connected or close coupled to
The transformer electrical losses which
include no-load losses (core loss) and
load losses (winding losses).
A static electrical device which by
electromagnetic induction transforms
energy at one voltage or current to
another at the same frequency.
Normal, routing production tests
include: (1) core loss (excitation loss
or non-load loss); (2) load loss –
winding or copper loss; (3) Impedance;
(4) Hi-pot – high voltage between
windings and ground; (5) Induced –
double induced two time normal
voltage. Optional special tests include:
(a) Heat Run – temperature testing;
(b) Noise tests – sound level measurement
(c) Impulse tests – BIL tests.
Electrical noise or voltage disturbance
that occurs between phase and neutral,
or from spurious signals across the
metallic hot line and the neutral
The change in secondary voltage which
occurs when the load is reduced from
rated value to zero, with the values of
all other qualities remaining unchanged.
Regulation may be expressed in percent
(per unit) on the basis or rated
secondary voltage at full load.
See Load Losses.
A three phase connection with similar
ends of each phase connected together
at a common point which forms the
electrical neutral point which is typically
Special transformer connection
commonly used with grounding
transformers. See also grounding