Types of Transformer
-
Single
phase transformer
-
Three
phase transformer
- Single phase transformer
- Three phase transformer
-
Single
phase transformer
- Single phase transformer
Single-phase
transformers accept single-phase AC power and output single-phase AC power,
typically at a higher or lower voltage level. Energy is transferred from one
circuit to one or more circuits via electromagnetic induction.
Operation
A
single-phase transformer is a type of power transformer that utilizes single-phase alternating
current, meaning the transformer relies on a voltage cycle that operates in a
unified time phase. They are often used to step-down long distance and
localized transmission currents into power levels more suitable for residential
and light-commercial applications. The ratio of primary (input) windings to
secondary (output) windings determines the change in current. Single-phase
transformers with a 1:1 ratio can be used to isolate circuits. Single-phase
transformers abide by Ohm's law, and outside of minor inherent loss due to
heat, do not create or remove power.
·
Single-phase
transformers are more popular than three-phase transformers in non-urban areas,
as the cost of a three-phase distribution network is much higher, and the
overall electrical demand is lower. The highest voltage available in a
single-phase network is regulated by utility infrastructure and industrial
regulations. A single-phase transformer is frequently used for power
distribution and voltage reduction for residential and commercial applications.
When used with appliances, the lower voltage output is often rectified into DC
current before powering appliances, such as a computer.
·
High-voltage
systems typically employ three-phase transformers to
power apartment buildings, retail centers, factories, offices, and other
large-scale structures, as well as electric motors—single-phase power supplies
do not produce the rotating magnetic field required to induce rotation.
Three-phase power systems are more common in cities, where dense power supply
demands require transformers that route hundreds or thousands of kVA.
Types
The
following transformer types are commonly manufactured to accept and output
single-phase AC power.
Audio transformer: removes ground noise from audio
signals by encasing the transformer in magnetic shieldings.
Autotransformer:
typically used in low power applications to connect circuits with different
voltage classes. It contains only one winding, cannot isolate circuits, and is
usually smaller, lighter, and cheaper than other transformers. The voltage
source and electrical load are connected to two taps, and voltages are
determined by tapping the winding at different points. An autotransformer with
an adjustable tap is known as a variac or variable transformer, and an example
is pictured at right.
Buck-boost
transformer:
this type of transformer adjusts a voltage level to device specifications. They
are commonly used as circuit isolators.
Constant-voltage transformer (CVT): these
produce a relatively constant output voltage, despite potentially large
variances in the input voltage.
Constant-current
transformer:
also called a regulator, it has a self-adjusting secondary winding that provides
a consistent output current for any load within its dynamic range. It is common
for streetlight applications.
Distribution transformer: this is the oft-seen,
pole-mounted transformer that steps-down current for light-duty electrical
applications.
Flyback transformer: to produce a high-voltage
output, the transformer stores energy in its magnetic windings for a short
period of time.
Generator
step-up transformer: steps-up voltage levels to a suitable long-distance
transmission voltage level.
Harmonic mitigating transformer: utilizes
phase-shifting, electromagnetic flux cancellation, and source impedance to
decrease harmonic currents in distribution systems, which ultimately lowers
transformer operating temperature.
Impedance
matching transformer: are used to minimize signal reflection from an
electrical load and often have a 1:1 turn ratio. A common example of an
impedance-matching transformer would be a balun, which is used to connect two
circuits of mismatched impedance, such as a balanced line of two conductors
carrying equal currents in opposite directions that is connected to an
unbalanced line of one conductor carrying current and a ground.
Industrial control transformer: supply power to
constant-current or constant-voltage devices that may be sensitive to
variations in electrical supply, such as solenoids, relays, or other
electromechanical devices.
Isolation
transformer:
is not used to step-up or step-down voltages, but rather to buffer circuits
from each other.
Leakage transformer (stray-field transformer):
maintains a high leakage inductance by loosely coupling the magnetic fluxes of
the primary and secondary windings. This makes the transformer short-resistant,
an important characteristic of transformers for welding operations.
Lighting
transformer:
supplies low voltages for lighting and other light-duty applications.
Medical
transformer:
leakage current, high potential requirements, temperature class, and current
and thermal fusing are the primary concerns of medical transformers due to the
sensitive environments in which they are employed. They are carefully regulated
by law and industrial standards.
Multi-ratio
transformer:
a transformer with several outputs with each output tap corresponding to a
different transformer ratio.
Neutral grounding transformer: protects power
transformers and generators from harmful fault currents. When a fault
occurs, a voltage is induced in the open delta and there is a voltage drop in
the connected resistor.
Power transformer: convert voltages from one level or
phase to another for widespread power distribution.
Rectified
transformer:
converts AC to DC.
Resonant
transformer:
a capacitor is placed across one or both windings to function so the circuit
can be tuned.
Solar
power transformer: the transformer can be incorporated as part of a
single-phase string inverter, or as a step-up transformer to connect PV plants
to a grid.
Substation
transformer:
a step-down transformer that converts transmission-level voltages to
distribution-level voltages.
Configurations
Variations
in transformer design enable use for specific applications.
Windings
The ratio
of primary (input) coils to secondary (output) coils determines if the voltage
is increased or decreased after routing through the transformer. Some
transformers have an adjustable turn ratio, while others maintain 1:1 (or near
1:1) ratio to simply isolate circuits. Other transformers utilize a single
coil, and voltage is transmitted by tapping the coil at an intermediate point.
Winding configuration
·
Single: one primary winding that accepts one
nominal voltage
·
Dual: dual primary windings that accept two
nominal voltages
·
Quad
(2+2): dual
primary windings and each winding accepts two nominal voltages
·
5-lead: primary winding can accept five
nominal voltages
·
Ladder: consists of cascading windings that
create a series of inductances between adjacent windings
Cooling
·
Oil-filled transformers rely on a strong
dielectric oil to insulate components and dissipate heat. Mineral oil,
synthetic-ester, and silicone-based fluids have replaced PCBs. Some
transformers may utilize radiators, filters, fans, pumps, or heat exchangers to
manage transformer oil, depending on the application.
·
PCB-filled transformers are replaced by
other cooling methods when the fluid expires, as PCB has been identified as a
carcinogen for more than 50 years. Many PCB transformers remain in operation
today, however, and may still be sought in less regulated markets.
·
Transformers
that use water to
cool components are immersed in oil, but cool water is fed through copper pipes
below the oil surface to improve circulation and heat exchange. Another method
is to pump heated oil out of the transformer through tubes that are doused in
water.
·
Dry/air-cooled transformers contain two windings
that face each other but does not contain a core. The windings are cooled via
convection, which might be supplemented with a ventilated enclosure and blowers
or fans.
·
Encapsulated transformers utilize a
dielectric, thermal management resin to seal the transformer components from
contaminants.
Core
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