Types of Transformers on the Basis of Core Arrangement
On the basis of core and winding arrangement, following are the main types of transformers:
- Core type transformer
- Shell type transformer
- Berry type transformer
Core Type Transformer
In the core type transformer magnetic core is made from ‘L’ shape strips. The core type transformer consists of an iron core surrounded by windings. The core of this transformer has two limbs.
Each limb carries the same flux. Therefore, the area of both limbs is equal.
The low voltage winding is placed next to the core and high voltage winding is placed over it. Proper insulation is provided in between core, low voltage winding and high voltage windings.
Shell Type Transformer
In the core type transformer, the iron core is surrounded by the windings whereas, in the shell type transformer, the windings are surrounded by the iron core. The core of shell type transformer is made from ‘E’ and ‘I’ strips.
The laminations of this transformer have three limbs. The side limbs carry half of the flux whereas central limb carries the whole of the flux. Therefore, the width of the central limb is more than that of the outer limbs.
Both the windings are placed on the central limb concentrically or side by side. The low voltage winding is placed next to the core and high voltage winding is placed over it. Proper insulation is provided in between core, low voltage winding and high voltage windings.
Types of Transformers on the Basis of Transformation Ratio
The transformation ratio of the transformer may be defined as the ratio of the secondary voltage to the primary voltage of the transformer. It is denoted by K.
Therefore, transformation ratio K = V2/V1
And K = E2/E1 = N2/N1 = I1/I2 also.
Where V1, E1, N1 are the supply voltage, induced EMF, winding turns of the primary winding respectively. And V2, E2, N2 are output voltage, induced EMF, winding turns of secondary winding respectively.
On the basis of the value of K, types of transformers are as follows:
The transformers having K > 1 i.e. N2 > N1 are known as the step-up transformer. In such type of transformers, we get high output voltage as compared to the applied voltage, hence the name step-up.
The transformers having K < 1 i.e. N2 < N1 are known as the step-down transformer. In such type of transformers, we get low output voltage as compared to the applied voltage, hence the name step-down.
The transformers having K = 1 i.e. N2 = N1 are known as the one-to-one transformer. In such type of transformers output voltage is equal to the input voltage. The main function of such transformer is to provide isolation between input and output circuit, hence this transformer is also known as the isolation transformer.
Types of Transformers on the Basis of Applications
The transformers are often classified on the basis of the purposes for which they are used. Following are the important types of transformers on the basis of applications:
These transformers are used at the power plants to step-up the generated voltage for transmission purposes and to step down the voltage at the receiving substations. These are large size transformers.
These transformers are usually operated near the full load which would cause high copper loss. Thus, to have minimum losses, such transformers are designed with low copper losses and to give maximum efficiency at near the full load.
These transformers are used to step down the voltage at the distribution substations. The load on such transformers varies for all the 24 hours from no load to full load.
Such transformers are designed with low iron loss and to give maximum efficiency at about 75% of the full load to obtain high efficiency.
These transformers are used to measure high voltage, high current and to operate protective devices. To measure high voltage, it is stepped down with an instrument transformer which is known as the potential transformer (PT) and then applied to a voltmeter. Similarly, to measure high current, it is stepped down with an instrument transformer which is known as the current transformer (CT) and then applied to an ammeter.
To carry out the tests under high, voltages testing transformers are used to step-up the voltage to a very high value.
These are used to operate welding sets, rectifiers, electric furnaces etc.
Transformer — 4| Objective Type Question Answers
#1 Which of the following is the main advantage of an auto-transformer over a two winding transformer ?
Saving in winding material
#2 During short-circuit test, iron losses are negligible because
the voltage applied on primary side is low
#3 The change in volume of transformer cooling oil due to variation of atmospheric temperature during day and night is taken care of by which part of transformer
#4 An ideal transformer is one which has
no losses and magnetic leakage
#5 When a given transformer is run at its rated voltage but reduced frequency, its
core flux density is increased.
#6 If the supply frequency to the transformer is increased the iron loss will
#7 Negative voltage regulation is indicative that the load is
#8 Iron loss of a transformer can be measured by
low power factor wattmeter
#9 When secondary of a current trans-former is open-circuited its iron core
will be hot because of heavy iron losses taking place in it due to high flux density
#10 Which type of winding is used in 3-phase shell type transformer ?
#11 For the parallel operation of single-phase transformers it is necessary that they should have
#12 The transformer oil should have………volatility and………. viscosity.
#13 The function of breather in a transformer is
to arrest flow of moisture when outside air enters the transformer.
#14 The secondary winding of which of the following transformers is always kept closed ?
#15 The size of a transformer core will depend on
frequency and area of the core
#16 Natural air-cooling is generally restricted for transformers, up to
#17 A shell-type transformer has
reduced magnetic leakage
#18 A transformer can have regulation closer to zero
on leading power factor
#19 Reduction in core losses and increase in permeability are obtained with transformer employing
core built-up of laminations of cold rolled grain oriented steel
#20 In a power or distribution transformer about 10 pm cent end turns are heavily insulated
to withstand the high voltage drop due to line surge produced by the shunting capacitance of the end turns
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- Single Phase Transformer Working Principle
- Ideal Transformer
- Construction of Three Phase Transformer
- Types of Transformers
- Equivalent Resistance and Reactance of Transformer
- Equivalent Circuit of Single Phase Transformer
- Power Loss in a Transformer
- Open Circuit Test of Single Phase Transformer
- Short Circuit Test on Single Phase Transformer
- Transformer Efficiency
- Regulation of Transformer
- Instrument Transformers
- Polarity of Transformer Windings
- Significance of Vector Group of Transformer
- Buchholz Relay Construction | Working
- Why current transformer secondary should not be opened
- Dielectric Strength Test of Transformer Oil
- Transformer Moisture Removal Process