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TRANSFORMER Definition

Type of transformer

How it works?

Parts in the transformerApplication of power transformer : Distribution Transformer

TRANSFORMER

Definition Power transformer is a static electrical device which transforms electrical

energy from one circuit to another without any direct electrical connection and

with the help of mutual induction between two windings. It transforms power

from one circuit to another without changing its frequency but may be in

different voltage level.

Types of Transformer

Step-up TransformerOn a step-up transformer there are more turns on the secondary coil

than the primary coil. The induced voltage across the secondary coil is

greater than the applied voltage across the primary coil or in other words

the voltage has been “stepped-up”.

Step-down TransformerA step down transformer has less turns on the secondary coil that

the primary coil. The induced voltage across the secondary coil is less the

applied voltage across the primary coil or in other words the voltage is

“stepped-down”.

How it Works

The working principle of transformer depends upon Faraday's law of

electromagnetic induction. According to these Faraday's laws,

"Rate of change of flux linkage with respect to time is directly

proportional to the induced EMF in a conductor or coil".

Whenever we apply alternating current (AC) to an electric coil, there will

be an alternating flux surrounding that coil. If we bring another coil near the

first one, there will be an alternating flux linkage with that second coil. As the

flux is alternating, there will be a rate of change in flux linkage with respect to

time in the second coil. Naturally electromotive force (EMF) will be induced in

it as per Faraday's law of electromagnetic induction. The winding which takes

electrical power from the source, is generally known as primary winding. The

winding which gives the desired output voltage due to mutual induction in the

transformer, is commonly known as secondary winding.

The relationship between the voltage and the number of turns in each coil

is given by:

Transformers are usually assumed to be 100% efficient. Due to this, the

power in the primary coil has to be equal to the power in the secondary coil, as

per the law of conservation of energy.

Power in primary coil = Power in secondary coil

Parts of Power Transformer

1) Laminated core- Core or laminated core is used to support the windings in a transformer

2) Windings - Windings consists of several turns of copper coils bundled together an

each bundles are connected in series to form a winding

3) Insulating Materials- To isolate the primary and secondary winding from each other transformer

core

4) Transformer oil- Acts as an important functions of insulation to cool down the core and coil

assembly

5) Breather - Acts as an air filter for the transformer and controls the moisture level

inside a transformer

6) Conservator - To conserves the transformer oil

7) Tap changer - To balance the voltage variations

8) Cooling tubes- To cool the transformer’s oil

9) Buchholz relay- It is used to sense the faults occurring inside the transformer

10) Explosion vent- Is used to expel the boiling oil in the transformer during heavy internal

faults in order to avoid explosion of transformer

Application of power transformer

Definition of Distribution Transformer.

A distribution transformer or service transformer is a transformer that

provides the final voltage transformation in the electric power distribution

system, stepping down the voltage used in the distribution lines to the level used

by the customer. The invention of a practical efficient transformer made AC

power distribution feasible; a system using distribution transformers was

demonstrated as early as 1882.

If mounted on a utility pole, they are called pole-mount transformers. If

the distribution lines are located at ground level or underground, distribution

transformers are mounted on concrete pads and locked in steel cases, thus

known as pad-mount transformers.

Distribution transformers normally have ratings less than 200 kVA,

although some national standards can describe units up to 5000 kVA as

distribution transformers. Since distribution transformers are energized for 24

hours a day, reducing iron losses has an important role in their design. As they

usually don't operate at full load, they are designed to have maximum efficiency

at lower loads. To have a better efficiency, voltage regulation in these

transformers should be kept to a minimum. Hence they are designed to have

small leakage reactance.

Uses of Distribution Transformer

Distribution transformers are normally located at a service drop, where

wires run from a utility pole or underground power lines to a customer's

premises. They are often used for the power supply of facilities outside

settlements, such as isolated houses, farmyards or pumping stations at voltages

below 30 kV. Another application is the power supply of the overhead wire of

railways electrified with AC. In this case single phase distribution transformers

are used.

The number of customers fed by a single distribution transformer varies

depending on the number of customers in an area. Several homes may be fed off

a single transformer in urban areas; rural distribution may require one

transformer per customer. A large commercial or industrial complex will have

multiple distribution transformers. Pad mount transformers are used in urban

areas and neighbour hoods where the primary distribution lines run

underground. Many large buildings have electric service provided at primary

distribution voltage. These buildings have customer-owned transformers in the

basement for step-down purposes. In a secondary network system as used in

urban areas, many distribution transformers may be connected in parallel, each

equipped with its own network protector circuit breaker to isolate it from the

secondary network in case of a fault.

Distribution transformers are also found in the power collector networks of

wind farms, where they step up power from each wind turbine to connect to a

substation that may be several miles (kilometers) distant.