Power Transformers: Specifications, Construction and Applications

Ans. The mechanical equipment that converts mechanical energy into electrical form of energy is called a Generator. Industrial and agricultural sectors often make use of generators. Generators are constructed using the principle of law of electromagnetic field. The two types of generators are AC generator and DC generator. Generators have a rectangular coil, called an armature that consists of multiple copper wires. The armature keeps changing its position over several time intervals.

Ans. Based on their necessity, transformers can be classified into:

1. Power Transformers
2. Indoor Transformers
3. Outdoor Transformers
4. Distribution Transformers
5. Measurement Transformers

Ans. AC generators alternate current and convert mechanical energy into electrical energy. Such generators are also known as alternators. AC generators are rated using the unit kilovolt-amperes. The two types of AC generators are Induction generators and synchronous generators. AC generators don’t require much maintenance. The losses are minimum. They are smaller in size when compared to other generators.

Ans. The four types of transformers are:

• Step up transformer
• Step down transformer
• Power transformer
• Isolation transformer

Ans. Commonly, there are two types of transformers: step up transformers and step down transformers. However, transformers can also be classified based on cooling methods and designs.

There are three types of transformers based on cooling method:

1. Air blast type
2. Oil filled water cooled type
3. Oil filled self cooled type

There are two types of transformers based on design:

1. Shell type transformer
2. Core type transformer

Ans. Working of a transformer follows the principle of mutual inductance. The two windings are close to each other but they have no conductive connection. The coil windings have magnetic induction. A sinusoidal voltage energises the primary coil winding. The secondary coil winding feeds the load. The magnetic field created transforms the energy from primary circuit to secondary circuit.

Ques. How to identify a Power Transformer? (2 marks)

Ans. Transformers have a variety of uses. Some of them are:

1. Transformers protect circuits from damage caused by high voltage current.
2. They help in regulating the flow of current inside the circuit.
3. Transformers aid in controlling the voltage so that the battery charging process is easier.
4. They help in the steel manufacturing process by regulating the current for welding and melting of steel.
5. Transformers are used for changing the alternating voltage.

Ans. Distribution Transformers: The power generated can be distributed to distant and far away locations using distributing transformers. It can distribute power for household purposes as well as in the industries.

Measurement Transformers: Measurement Transformers help in measuring power, voltage, current, etc.

Ans. DC generator converts mechanical form of energy into current electricity. The three types of DC generators are:

1. Separately excited DC generators
2. Permanent magnet DC generators
3. Self excited DC generator

Self excited DC generators also include shunt wound generator, series wound generator, and compound wound generator.

DC generators don’t require any shielding from the radiation. Hence, the cable cost of such generators is less. The field winding determines the operating characteristics of such generators.

Ans. For maximum power transfer, the load resistance (referred to the primary) must be equal to the source resistance.

Ans. 

Ans. Voltage regulation is the change in secondary terminal voltage from no load to full load at a specific power factor of load and the change is expressed in percentage.

E₂ = no-load secondary voltage

V₂ = full load secondary voltage

Voltage regulation for the transformer is given by the ratio of change in secondary terminal voltage from no load to full load to no load secondary voltage.

Voltage regulation \(= \frac{{{E_2} - {V_2}}}{{{E_2}}}\)

It can also be expressed as,

Regulation \(= \frac{{{I_2}{R_{02}}\cos {ϕ _2} \pm {I_2}{X_{02}}\sin {ϕ _2}}}{{{E_2}}}\)

Regulation = %R cos ϕ ± %X sin ϕ

+ sign is used for lagging loads

- ve sign is used for leading loads

Where %R = ohmic drop

%X = reactance drop

Calculation:

Ohmic loss (%R) = 1%

Reactance drop (%X) = 5%

Power factor = cos ϕ = 0.8 lagging

∴ sin ϕ = 0.6

Regulation = %R cos ϕ ± %X sin ϕ

Ans. Transformer is used to convert low voltage (or high current) to high voltage (or low current) and high voltage to low voltage at constant power.

It works on the principle of mutual induction.

• The primary coil has Np turns. The other coil, called the secondary coil, has Ns turns.
• Generally, the primary coil works as the input coil and the secondary coil works as the output coil of the transformer.
• When an AC voltage is applied to the primary coil, the resulting current produces an alternating magnetic flux that links the secondary coil and induces an emf in it. The value of this emf depends on the number of turns in the secondary.

• In a transformer, the voltage in secondary is calculated by \(\frac{N_{s}}{N_{p}}=\frac{V_{s}}{V_{p}}\)
  Here,Np and Ns are the numbers of turns in the primary and the secondary coils respectively and Vp and Vs are the RMS voltages across the primary and secondary respectively.
• In a transformer, the load is connected to the secondary coil while the primary coil of a transformer is connected to an AC source.
• Mutual induction: By a change in the current in a circuit that is linked to another by the flux lines of a magnetic field, the production of an electromotive force in the circuit is called mutual induction.

Ans. 

• Ferrite core is a type of magnetic core made of ferrite on which the windings of electric transformers and other wound components such as inductors are formed.
• It is used for its properties of high magnetic permeability coupled with low electrical conductivity (high resistance)
• It helps in preventing eddy currents