- Air Cooled:
A transformer which uses air as the cooling medium. This may be natural
draft cooling by convection or forced air with the use of fans.
- Ambient Noise
Level: The existing or inherent sound level of the area surrounding
a transformer installation measured in decibels.
- ANSI: American
National Standards Institute is the recognized body which specifies
the standards on transformers.
- ANSI C 89.1
and C 57.12
are the standards most often used for dry type transformers.
- Auto-Transformer:
A transformer which has only one winding per phase, part of which
is common to both primary and secondary circuits.
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- Banked: This
term is used when two or more single-phase transformers are connected
or banked together to supply power to a three-phase load. The three
single-phase transformers banked together will produce a KVA capacity
of three times the nameplate rating of each of the single-phase transformers.
Example, three 5 KVA single-phase transformers connected together
for a three-phase load will have a KVA capacity of 15 KVA.
- BIL: Basic Insulation
Level is a measure of the ability of the insulation system to withstand
very high voltage surges. For example, a 600 volt class transformer
has a 10 KV BIL rating.
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- Center Tap: A
reduced capacity tap at the mid-point in a winding.
- Certified Test:
Actual production or laboratory tests which certify values as having
been taken on a specific item, on a specific order.
- Compensated Transformer:
A transformer with a turns ratio which provides a higher than rated
voltage at no load rated voltage at rated load.
- Continuous Rating:
Refers to the load that a transformer can handle indefinitely without
exceeding the specified temperature rise.
- Conductor Losses:
Losses caused by the resistance of the transformer winding and usually
measured at 25, 50, 75, and 100 percent of load.
- Core Loss: Losses
caused by a magnetization of the core and its resistance to magnetic
flux.
- Current Transformer:
A transformer designed to have its primary winding connected in series
with the circuit and used for transforming current to a value suitable
for measurement or control.
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- Decibel (dB):
The standard unit used in the measurement of sound intensity.
- Delta (): A standard
three-phase connection in which each phase winding is connected in
series to form a closed loop.
- Delta Wye (-Y):
The term used when indicating a method of connection for both primary
and secondary windings of a three-phase transformer bank.
- Dielectric Tests:
A series of tests conducted at much higher than rated nameplate voltage
to determine the effectiveness of insulating materials and electrical
clearances.
- Distribution Transformer:
Any transformer rated between 3 and 500 KVA, inclusive with a primary
voltage of 601 volts or greater.
- Dry Type Transformer:
A dry type transformer is one which does not employ a liquid as a
cooling or insulating medium.
- Dual Winding:
A winding that consists of two separate windings which can be connected
in series to handle a specific voltage and KVA, or in parallel to
handle the same KVA at one half the series connected voltage.
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- Electrostatic Shield:
A grounded conductor sheet placed between the primary and secondary
winding to greatly reduce or eliminate line to line or line to ground
noise. It is often referred to as a Faraday shield.
- Encapsulated:
A style of dry type transformer utilizing a solid resin to encase
and seal the core and coil assembly.
- Exciting Current:
The current which maintains the excitation of a transformer (the current
that flows in the primary) when the load is disconnected. Usually
expressed in percent of the rated current of the winding.
- Extended Winding:
A winding with additional turns to provide application of a higher
voltage. This effectively changes the turns ratio of the transformer
when the extended winding is employed in the circuit. Example: FCAN
taps.
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- FCAN: Full capacity
above nominal taps. The designation used to indicate that a transformer
will deliver rated KVA when connected to a voltage source which is
higher than rated voltage.
- FCBN: Full capacity
below nominal taps. Same as FCAN except that the taps are below rated
voltage.
- Fan Cooled: A
means of accelerating heat dissipation to lower the temperature rise
of the transformer. This has the effect of increasing the transformer
rating.
- Filter Press:
A device for filtering and absorbing moisture from oil. Liquid is
force-circulated through absorbent filter pads.
- Flexible Connector:
A pliable conductor designed to compensate for thermal expansion and
contraction, or reduce the transmission of objectionable noise.
- Frequency: The
number of times an AC voltage will alternate from positive to negative
and back again within a specified period of time, usually expressed
in cycles per second and identified as Hz as in 60 Hz.
- Full Capacity Tap:
Tap that is designed to deliver the rated capacity of the transformer.
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- Harmonic
Mitigating Transformer: A transformer whose primary function is
the elimination of harmonics produced by certain types of non-linear
loads, such as computer power supplies and a number of special drives.
- Hazardous
Duty Transformer: A transformer designed for use in a typically
corrosive environment as described by Article 500 of the NEC, Class
1, Division 2, Group C and D.
- Hertz (Hz): A
term for AC frequency in cycles per second. Transformers rated for
60-Hertz service should not be applied to 50 Hertz, as overheating
will occur. Certain transformers are rated 50/60 Hertz and therefore,
suitable for either frequency.
- High Resistance Transformer:
A design which has high leakage to reactance to limit the output current
to a designated value in the event of a fault. Also called Energy
Limiting transformer.
- Hi Pot: A standard
dielectric test to check insulating materials and clearances between
windings and between windings and ground.
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- Impulse Tests:
The test employed to determine Basic Insulation Level (see also BIL).
- Impedance: The
vector sum of resistance and reactance, which limits the current flow
in an AC circuit. Impedance is identified in percentage and is used
to determine the interrupting capacity of circuit breakers, which
protect the primary circuit.
- Induced Potential
Test: A standard dielectric test which verifies the integrity
of insulating materials and electrical clearances between turns and
layers of a transformer winding.
- Inrush Current:
An abnormally high current which is occasionally drawn when a transformer
is first energized, due to residual flux in the core.
- Instrument Transformer:
A transformer designed to transform the conditions of current or voltage
and phase position in the primary with a specified accuracy of the
secondary circuit.
- Insulating Material:
Organic or inorganic substances which prevent or greatly reduce the
current flow between live parts or between live parts and ground.
- Insulating Transformer:
One in which the primary winding is insulated from the secondary winding.
- Interleaving:
A method of winding where the primary and secondary are wound in sections
with a section of the primary between two sections of the secondary
and vice versa. This technique is used to reduce the leakage reactance
of the transformer when desirable to do so. Industrial control transformers
frequently have interleaved windings.
- Isolating Transformer:
A transformer which insulates the primary circuit from secondary circuit
as with an insulating transformer, but frequently with no voltage
change.
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- Jack Pads:
Structural member at bottom of transformer to accommodate hydraulic
jacks which lift onto rollers for moving into position.
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- K Factor:
A relative number (4, 9, 13, 20, 30, etc.) assigned to electrical
apparatus such as a transformer to express the devices compensating
ability in dealing with additional, non-fundamental loading. This
loading is typically caused by harmonics.
- KVA: Kilovolt
Ampere rating designates the output which a transformer can deliver
at rated voltage and frequency without exceeding a specified temperature
rise.
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- Load: The KVA
or VA requirement which the transformer must supply.
- Load Center Unit
Substation Transformer: A transformer that is mechanically and
electrically connected to and coordinated in design with switch-gear
or motor control assemblies.
- Load Losses:
The losses which are the result of a current flowing to the load.
Load losses would include all losses incurred above and beyond the
no-load losses.
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- Multiple Winding:
A winding which consists of two or more sections that can be paralleled
for specific mode of operation.
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- NEMA Standard:
Any standard recommended by the National Electrical Manufacturers
Association.
- Network Transformer:
A transformer which is electrically and mechanically connected to
and coordinated in design with switch-gear or motor control assemblies
for use on a utility network power system.
- Noise Attenuating
Transformer: A transformer designed to minimize electrical noise
associated with certain loads.
- No-Load Losses:
The losses incurred when a transformer is excited, but without a
load connected to the secondary. These include core loss, dielectric
loss, and exciting current I2R loss.
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- Overload: When
a transformer is overloaded, excessive heat develops, and the insulation
system begins to break down out of proportion to the amount of overload.
Life expectancy of the transformer is greatly decreased due to heat
exceeding the rating of the insulation system.
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- Parallel Operation:
Transformers or transformer windings may be connected in parallel
provided that the electrical characteristics are suitable for such
operation.
- Percent IR (%IR)
Percent Resistance: The voltage drop due to conductor resistance
at rated current expressed in a percent of the rated voltage.
- Percent IX (%IX)
Percent Reactance: The voltage drop due to reactance, at rated
current, expressed in a percent of the rated voltage.
- Percent IZ (%IZ)
Percent Impedance: The voltage drop due to impedance, at rated
current, expressed in a percent of the rated voltage.
- Phase: Classification
of an AC circuit. Usually, circuits are rated single-phase two wire
or three wire or three-phase three wire or four wire. Single-phase
transformers can be used on a three-phase source when two wires
of the three-phase system are connected to the primary of
the single-phase transformer. The secondary will be single-phase.
- Polarity: A
designation of the relative instantaneous direction of the current
in a secondary lead as compared with a primary lead. The two leads
are said to be of the same polarity when, at any instant, the currents
in the two leads are flowing in the same direction as if the leads
were a single piece of wire. The polarity of a single-phase transformer
is classed as either additive or subtractive.
- Polyphase:
More than one phase.
- Potential Transformer:
A transformer that is designed to have its primary winding connected
parallel with a circuit and used for transforming voltage to a value
suitable for measurement or control.
- Power Factor:
The ration of watts to volt amperes in a circuit. Expressed as %
watts / VA.
- Pressure Relief
Device: Used to relieve excessive pressure inside tank. Generally
operates at 71/2 psi. Self-resealing with target indicator to show
operation. Alarm contacts are optional.
- Pressure Vacuum
Bleeder Valve: Automatic valve which opens and closes to maintain
internal pressure within predetermined limits.
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- Radiators:
Tank extensions used to assist cooling the oil and transformer.
Panel type is generally used for better efficiency and appearance.
- Rating: This
refers to the characteristics such as volt ampere capacity, voltages,
frequency and temperature rise for which the transformer is designed.
- Ratio: A reference
to either the turns ration or to the voltage ration of the transformer.
It's the ration between the primary and the secondary. For example,
a transformer with a 480-volt primary and a 120-volt secondary has
a ratio of 4 to 1.
- Reactance:
A component of impedance produced by either inductance or capacitance
in an AC circuit.
- Reactor: A
device, generally a single winding on an air core or an iron core,
which produces a specific amount of inductive reactance for which
it is designed.
- Rectifier Transformer:
A transformer designed to supply the AC input to a rectifier at
the value necessary to obtain the desired DC output. Also to have
the ability to withstand the usual heating effects caused by rectifier
commutation or ripple.
- Reduced Capacity
Taps: Tap that is not designed to deliver the rated capacity
of the transformer.
- Regulation:
The percent change in output voltage from full load to no load.
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- Scott Connection:
A transformer connection usually used to get a two-phase output
from the secondary of a transformer with a three-phase input to
the primary, or vice versa. It can also be used to provide three-phase
to three-phase transformation.
- Secondary Winding:
The transformer winding connected to the load or output side.
- Sealed Dry Transformer:
dry type core and coils in a tank containing an inert gas such as
nitrogen or Freon under slight pressure.
- Series/Multiple:
A winding consisting of several sections, which can be connected
for series or parallel operation.
- Star Connection:
See "Wye Connection".
- Step Down Transformer:
One in which the high voltage winding is connected to the input
or power source and the low voltage winding to the output or load.
- Step Up Transformer:
A transformer in which the low voltage winding is connected
to the power source or input and the high voltage winding is connected
to the output load.
- Sudden Pressure
Relay: Pressure switch device, which operates instantaneously
to disconnect transformer from the line. Sudden pressure is usually
caused by an internal transformer fault.
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- T-Connection:
A Scott connected three-phase transformer utilizing two primary
and two secondary coils called the main and teaser coils.
- Tap: A connection
provided in a transformer winding which has the effect of changing
the nominal voltage ratio of the transformer. The taps are usually
placed on the high voltage winding to correct for high or low voltage
conditions found on the low voltage output side. Taps are expressed
as either full capacity above nominal (FCAN) or full capacity below
nominal (FCBN).
- Temperature Indicator:
Measures winding temperature. Has provision for resetting maximum
temperature indication.
- Temperature Rise:
The temperature increase over ambient due to load. This is measured
as either average rise by resistance or as hot-spot.
- Thermal Overload
Relay: Allows loading transformer to full thermal capacity by
analyzing loads, temperatures and transformer time constant. Operates
contacts for alarm and/or forced air cooling fans.
- Transformer:
A transformer is a static electrical device which by electro-magnetic
induction, transfers electrical energy from one circuit to another
circuit usually with changed values of voltage and current.
- Turns Ratio:
See "Ratio".
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- Volt Amperes:
The current flowing in a circuit multiplied by the voltage of that
circuit. An expression of the output rating of a transformer.
- Voltage Ratio:
See "Ratio".
- Voltage Regulation:
See "Regulation".
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- Wye Connection:
A three-phase connection in which similar ends of each phase winding
are connected together at a common point which forms the electrical
neutral and often grounded.
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- Zig-Zag Transformer:
A transformer where the windings are physically manipulated
to achieve certain voltage and current phase relationships. A zig-zag
winding arrangement is commonly found in harmonic mitigating or
grounding styles of transformers.
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