![]() |
Transformers and Different Types |
Transformer is a electrical device which is used
to convert electrical energy of higher voltage to a lower voltage without
changes in frequency before and after the voltage transformation. It is mostly
used in distribution lines of urban areas. In this article we are going to see
about different 12 types of transformers used in the electrical.
They are Step-down, step-up,
isolation, variable, current, power, potential, auto, single phase, three
phase, air core and the iron core transformer. Where are they used, principle,
construction, operation and losses are properly described in below.
What is Transformer?
Definition : It is a electrical equipment which is used to convert electrical energy of higher voltage (usually
11kV-22kV-33kV) to a lower voltage (230V or 440V) without changes in frequency
before and after the voltage transformation.
Its main application is mainly within
sub-urban areas, public supply and industrial consumers. With given secondary
voltage, distribution transformer is usually the last in the chain of
electrical energy supply to households and industrial's.
Principle
A
transformer consists of two conductors called the primary winding and secondary
winding, and a steel core that magnetically links them together. These two
winding's can be considered as a pair of mutually coupled coils. At the instant
a primary winding is energized with AC(Alternating Current), a flow of
electrons begins. During the instant of switch closing, buildup of current and
magnetic field occurs.
As
current begins the positive portion of the sine wave, lines of magnetic force
develop outward from the coil and continue to expand until the current is at
its positive peak. The magnetic field is also at its positive peak. The current
sine wave then begins to decrease, crosses zero, and goes negative until it
reaches its negative peak. The magnetic flux switches direction and also reaches
its peak in the opposite direction.
DC(Direct
current) is not transformed, as DC does not vary its magnetic fields. It is
usually consists of two insulated winding's on a common steel core - with an
alternating current power circuit, the current changes continually 60 times per
second, which is standard in the United States. That means circuit frequency in
USA is 60 hertz. Other countries may use other frequencies.
In
Europe, 50 cycles per second is common. In India 50 Hz. Strength of a magnetic
field depends on the amount of current and number of turns in the winding. When
current is reduced, the magnetic field shrinks. When the current is switched
off, the magnetic field collapses.
Construction of Transformers
There is no internal moving parts in transformers,
and it transfers energy from one circuit to another by electromagnetic
induction method. External cooling may include heat ex changers, radiators,
fans, and oil pumps. Radiators and fans are evident in figure. The large size
tank at the top is a conservator.
![]() |
Construction |
They are typically used because a
change in voltage is needed everywhere. Power transformers are defined as
transformers rated 500 kVA and larger. Larger types are oil-filled for
insulation and cooling. The rating smaller than 500 kVA are generally called
distribution transformers.
If
the secondary coil has twice as many turns as the primary, it will be cut twice
as many times by the flux, and twice the applied primary voltage will be
induced in the secondary coil. The total induced voltage in each winding is
proportional to the number of turns in that winding.
E1
- Primary voltage.
I1
- Primary current.
E2
- Secondary voltage.
I2
- Secondary current.
N1
- Primary turns and
N2
- Secondary turns.
Formula
is,
E1/E2
= N1/N2 = I2/I1
The
current is inversely proportional to both voltage(Primary and secondary) and
number of turns. This means that if voltage is stepped up, the current must be
stepped down and vice versa. The number of turns(N) remains constant unless
there is a tap changer. The power output or input of a transformer equals volts
times amperes. If the small amount of loss is disregarded, input equals to output.
E1 x I1 = E2 x I2
Types of Transformers Classified by Application
1. Power level (From
fraction of a watt to many megawatts),
2. Application (Power supply, impedance matching, circuit isolation),
3. Frequency range (Power, audio, RF)
4. Voltage range (A few volts to about 750 kilo volts)
5. Cooling type (Air cooled, oil filled, fan cooled, water cooled, etc.)
6. Purpose of using (Rectifier, arc furnace, amplifier output, etc.)
7. Number of turns in the coils.
2. Application (Power supply, impedance matching, circuit isolation),
3. Frequency range (Power, audio, RF)
4. Voltage range (A few volts to about 750 kilo volts)
5. Cooling type (Air cooled, oil filled, fan cooled, water cooled, etc.)
6. Purpose of using (Rectifier, arc furnace, amplifier output, etc.)
7. Number of turns in the coils.
Step Down Transformers
It
is designed to reduce voltage from primary to secondary. If there are fewer
turns in the secondary winding than in the primary winding, the secondary
voltage will be lower than the primary voltage is called step down
transformers. It is used to down the voltage output for commercial usage. If 33kV, 22kV or 11kV is the primary voltage that we gives can get 230V
or 440V in the secondary coil is step down.
![]() |
Step Down |
Step Up Transformers
It
is designed to increase voltage from primary to secondary. If there are fewer
turns in the primary winding than in the secondary winding, the secondary
voltage will be higher than the primary voltage is called step up
transformer. If we set up primary coil has few winding less than
secondary can get higher voltage output in the secondary winding.
![]() |
Step Up |
Isolation Transformers
When the primary winding and the secondary winding have the same amount of turns there is no change in voltage and the ratio of coil turns also unity is called isolation transformer.Variable Transformers
The
primary coil and secondary coil have an adjustable number of turns which can be
selected without reconnecting is called the variable transformer.
The primary winding, which receives the energy and it is not always the high voltage
winding.
Current Transformers
These
types are used in electric metering for large load needed condition to reduce
the current range or level presented to the metering circuit in order to make
it more manageable and safe. A current transformer is a type of ‘instrument
transformer’ that is designed to provide a current in its secondary winding
which is accurately proportional to the current flowing in its primary winding.
Power Transformers
The types are selected based on the
application, with the emphasis toward custom design being more apparent the
larger the unit. It is available for step-up operation, primarily used at the
generator and referred to as generator step-up transformers, and for
step-down operation, mainly used to feed distribution circuits. This types are
available as single-phase or three-phase apparatus.
The power transformer
construction depends upon the application. This type intended for indoor use
are primarily of the dry type but can also be liquid immersed. For outdoor use,
types are usually liquid immersed.
Application : 1. Step-up operation – Generator
step-up.
2.
Step-down operation – Distribution circuits.
Potential Transformers
It
is a special type of transformer that allows meters to take readings from
electrical service connections with higher voltage than the meter is normally
capable of handling without at potential transformer. The types
are used with voltmeters, watt-meters, watt-hour meters, power-factor meters,
frequency meters, synchroscopes and synchronizing apparatus, protective and
relays, and circuit breakers.
Single
transformer can be used for a number of instruments if the total current
required by the instruments connected to the secondary winding does not exceed
the KVA rating.
Auto-Transformers
It is possible to obtain transformer
action by means of a single coil, provided that there is a tap connection
somewhere along the winding. Transformer having single winding are called auto-transformers.
It has the usual magnetic core but single winding, which is common to both the
primary and secondary circuits. The primary is always the portion of the
winding connected to the AC power source.
This type may be used to step up or
step down. If the primary is the total winding and is connected to a supply,
and the secondary circuit is connected across only a portion of the winding,
the secondary voltage is step down.
Single Phase Transformers
The type has two winding's, one is
primary and another one is secondary. It is mostly used in low voltage
applications as electronic devices. The type operate as a step down transformer
and decrease the commercial voltage value to the suitable value for the used
electronics supplying. Secondary side in the electronic devices, rectifier is
connected to convert AC voltage to the DC voltage.
Three Phase (3 Phase) Transformers
Three single phase units connected in
the three phase system is called three phase transformer. The
type is commonly used in the industries and plants for transmission and
distribution.
Air Core Transformers
If an AC is supplied to a coil, a
magnetic field is produced surrounding it.
If another coil is brought this magnetic field, emf is induced across
the second coil also as per Faraday's law. This induced emf in the second coil
can be utilized to a load. As in this method the flux is linked with both coils
through air. This arrangement is called air core transformer.
Iron Core Transformers
Primary and secondary winding's are
wound on multiple iron plate which provide a path to the generated flux. These
types are widely used transformers in which the efficiency is high compared to
the air core type.
Transformer Construction
There are three main parts in the distribution
transformer,
1.Winding 2.Magnetic core 3.Tank.
Winding
Winding
Where incoming(primary side)
alternating current generates magnetic flux, which in turn induces a voltage in
the secondary winding.
Magnetic Core
The Material allowing transfer of
magnetic field generated by primary coil to secondary coil by the principle of Faraday's electromagnetic induction. A core and winding's are called its Active Parts.
This is because these two are responsible for transformation.
Tank
Serving as a mechanical package to
protect active parts, as a holding vessel for transformer oil used for cooling
and insulation.
Bucholz Relay
It is a safety device mounted on some
oil-filled power transformers, equipped with an external overhead
conservator. It is used as a protective device sensitive to the effects of
dielectric failure inside the equipment. The Bucholz Relay is also called Gas
relay or pressure relay.
Losses
Perfectly
manufactured transformer would have no losses, and would therefore be hundred
percentage efficient. In practice energy is dissipated due both to the
resistance of the winding's, and to magnetic effects primarily attributable to
the core. Transformers are in general highly efficient, and large power
transformers like 100 MVA or above ratings may attain an efficiency as high as
99.75%. Small sizes such as a plug-in power brick used to power small consumer
electronics may be less than 80% efficient.
The losses of:
1. Coil resistance
1. Coil resistance
Current
flowing through the coils causes resistive heating of the conductors.
2. Eddy current
Induced currents circulate in the core and cause its resistive heating.
3. Stray losses
Not
all the magnetic field produced by the primary is intercepted by the secondary.
A portion of the leakage flux may induce eddy currents within nearby conductive
objects such as the transformer's support structure and be converted to heat.
The familiar hum or buzzing noise heard near transformers is a result of stray
fields causing components of the tank to vibrate, and is also from
magnetostriction vibration of the core.
4. Hysteresis losses
The
magnetic field is reversed at each time, a small amount of energy is lost to
hysteresis in the magnetic core.
5. Mechanical losses
The alternating magnetic field causes fluctuating electromagnetic forces between the coils of copper wire, the core and any nearby metalwork, causing vibrations and noise which consume power.
6. Magnetostriction
The flux in the core causes it to physically expand and contract slightly with the alternating magnetic field.
Types of Cables
Hope you understand this article about the what is transformer and different 12 types of transformers. In case of any doubt please comment below. Please follow our website for future updates. Thank you for visiting our website – Electrical2z.
One of the best article about the transformer.. Thanks a lot..
ReplyDelete12 different types of transformers is a one of the good article.
ReplyDeletePost a comment