Transformer and Type's transformer

Transformer is a statics device which is used for transfer the electrical power from one circuit to another circuit without change in frequency and it’s work on the fraday’s law of mutal induction. 

1. According to construction there are two types of transformer-

1. core type
2. and shell type.

     2.Generally there are five types of transformer according to services-

1. instrument transformer ,
2. step up transformer and step down transformer,
3. single phase and three phase transformer,
4. Power transformer,
5. Distribution transformer.

  Core type-

• In the core type transformer on the two core limb.
• it has only  one magnetic circuited or magnetic flux path .
• It is used for lower voltage level applications.
• It has less mechanical protection to coil .
• Here losses is more than the shell type transformer.
• maintenance and repairing of this transformer is very simple.
• It has two limbs .
• natural cooling is provided since more surface is exposes to atmosphere.

shell type-

• In shell type transformer winding is placed on mid arm of the core .
• It has two magnetic circuit or magnetic flux path .
• It is used for the higher voltage level.
• shell type transformer has less leakage flux hence less losses therefore better efficiency .
• It has better mechanical protection to coil.
• maintenance and repairing of this transformer is complex than core type transformer . 
• it has three limbs .
• In this transformer natural cooling is less effective so compressive type cooling is used like as air,water,nitrogen gas .

 Generally there are five types of transformer according to services.

Now we will briefly discusses one by one .

1. instrument transformer 

        Instrument transformers are typically used to operate instruments from high voltage lines or high current circuits, safely isolating measurement and control circuitry from the high voltages or currents. The primary winding of the transformer is connected to the high             voltage or high current   circuit, and the meter or relay is connected to the secondary circuit. Instrument transformers may   also be used as an isolation transformer so that secondary    quantities may be used without affecting the primary circuitry.

   isolation  transformer      means a transformer used to transfer electrical power from a source of alternating current (AC) power to some equipment or device while isolating the powered device from the power source, usually for safety reasons like that electric shock,and reduce the electromagnetic noise.And which have a ratio of 1 to 1 between the primary and secondary winding are often used to protect secondary circuits and individuals from electrical shocks between energized conductors and earth ground. Suitably designed isolation transformers block interference caused by ground loops. Isolation transformers with electrostatic shields are used for power supplies for sensitive equipment such as computers, medical devices, or laboratory instruments.

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2.step up transformer and step down transformer.

step up transformer 

• According to construction step up transformer have more  secondary winding turn than the primary winding turn.
• step up transformer which increase the voltage level and decrease the current ,we can see as show on above figure.   
• it is used for high voltage transmission line to substation .
• It is large size than step down transformer.

step down transformer

• According to construction in step down transformer primary winding turn is more than secondary winding.
• In step down transformer decrease the voltage and increase the current level ,as shown in above figure.
• It is used for distribution purpose like as use in village ,urban, factory.
•  It is small in size

3.single phase transformer

A single-phase transformer is an electrical device that accepts single-phase AC power and outputs single-phase AC. This is used in the distribution of power in non-urban areas as the overall demand and costs involved are lower than the 3-phase distribution transformer. They are used as a step-down transformer to decrease the home voltage to a suitable value without a change in frequency. For this reason, it is commonly used to power electronic appliances at residences. This article discusses an overview of a single-phase transformer.

What is a Single Phase Transformer?

Definition: A transformer is a device which converts magnetic energy into electrical energy. It consists of two electrical coils called as a primary winding and secondary winding. The primary winding of a transformer receives power, while the secondary winding delivers power. A magnetic iron circuit called “core” is commonly used to wrap around these coils. Though these two coils are electrically isolated, they are magnetically linked.

An electric current when passed through the primary of a transformer then a magnetic field is created, which induces a voltage across the secondary of a transformer. Based on the type of application, the single-phase transformer is used to either step-up or step-down the voltage at the output. This transformer is typically a power transformer with high-efficiency and low losses. The single-phase transformer diagram is shown below.

single-phase-transformer

Principle of Single Phase Transformer

The single-phase transformer works on the principle of Faraday’s Law of Electromagnetic Induction. Typically, mutual induction between primary and secondary windings is responsible for the transformer operation in an electrical transformer.

Working of Single Phase Transformer

A transformer is a static device that transfers electric power in one circuit to another circuit of the same frequency. It consists of primary and secondary windings. This transformer operates on the principle of mutual inductance.

When the primary of a transformer is connected to an AC supply, the current flows in the coil and the magnetic field build-up. This condition is known as mutual inductance and the flow of current is as per the Faraday’s Law of electromagnetic induction. As the current increases from zero to its maximum value, the magnetic field strengthens and is given by dɸ/dt.

This electromagnet forms the magnetic lines of force and expands outward from the coil forming a path of magnetic flux. The turns of both windings get linked by this magnetic flux. The strength of a magnetic field generated in the core depends on the number of turns in the winding and the amount of current. The magnetic flux and current are directly proportional to each other.

As the magnetic lines of flux flow around the core, it passes through the secondary winding, inducing voltage across it. The Faraday’s Law is used to determine the voltage induced across the secondary coil and it is given by:

N. dɸ/dt

where,

‘N’ is the number of coil turns

The frequency is the same in primary and secondary windings.

Thus, we can say that the voltage induced is the same in both the windings as the same magnetic flux links both the coils together. Also, the total voltage induced is directly proportional to the number of turns in the coil.

Let us assume that the primary and secondary windings of the transformer have single turns on each. Assuming no losses, the current flows through the coil to produce magnetic flux and induce voltage of one volt across the secondary.

Due to AC supply, magnetic flux varies sinusoidally and it is given by,

ɸ = ɸmax Sin ωt

The relationship between the induced emf, E in the coil windings of N turns is given by,

E=N (d∅)/dt

E=N*ω*ɸmax cosωtφ

Emax=Nωɸmax

Erms=Nω/√2*ɸmax=2π/√2*f*N*ɸmax

Erms=4.44 fNɸmax

Where,

‘f’ is the frequency in Hertz, given by ω/2π.

‘N’ is  the number of coil windings

‘ɸ’ is s the amount of flux in Webers

The above equation is the Transformer EMF Equation. For emf of a primary winding of a transformer E, N will be the number of primary turns (NP), while for the emf, E of a secondary winding of a transformer, the number of turns, N will be (NS).

Construction of Single Phase Transformer

A simple single-phase transformer has each winding being wound cylindrically on a soft iron limb separately to provide a necessary magnetic circuit, which is commonly referred to as “transformer core”. It offers a path for the flow of the magnetic field to induce voltage between two windings.

As seen in the figure above, the two windings are not close enough to have an efficient magnetic coupling. Thus, converging and increasing the magnetic circuit near the coils can enhance the magnetic coupling between primary and secondary windings. Thin steel laminations shall be employed to prevent power losses from the core.

Three phase transformer.