|
A.
- 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.
back to top
B.
- 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.
back to top
C.
- 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.
back to top
D.
- 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.
back to top
E.
- 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.
back to top
F.
- 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.
back to top
G.
back to top
H.
- 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.
back to top
I.
- 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.
back to top
J.
- Jack Pads:
Structural member at bottom of transformer to accommodate hydraulic
jacks which lift onto rollers for moving into position.
back to top
K.
- 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.
back to top
|
|
L.
- 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.
back to top
M.
- Multiple Winding: A
winding which consists of two or more sections that can be paralleled
for specific mode of operation.
back to top
N.
- 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.
back to top
O.
- 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.
back to top
P.
- 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.
back to top
R.
- 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.
back to top
S.
- 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.
back to top
T.
- 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".
back to top
V.
- 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".
back to top
W.
- 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.
back to top
Z.
- 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.
back to top |
