# Anna University Previous Year Question Papers for EEE 4th Semester

### Solved Anna University Previous Year Question Papers for EEE 4th Semester

In this post we have collected various questions asked in the Anna University Previous Year question papers(fourth semester) about single phase transformers.
These questions with answers will definitively helpful for you to prepare for your university exams as well as for attending technical interviews.

[1] What is an ideal transformer? [Dec-04]
The ideal transformer should have the following properties:

1. It has no losses
2. Its windings have zero resistance
3. It should have zero leakage flux (100% flux produced by primary links with the secondary)
4. Permeability of core is so high that negligible current is required to establish the flux in it.

[2] Why transformers are rated in KVA instead of KW?

• The copper loss (I2R) in the transformer depends on the current through the winding.
• The iron loss or core loss of the transformer core depends on the voltage as frequency of operation is constant.
• None of these losses depends on the power factor(cos Φ) of the load.
• So losses decide the temperature rise and hence the rating of the transformer.
• As the losses depends on V and I only, the rating of the transformer is specified as the product
of these two parameters (V x I).
• Thus the transformer rating is in KVA and not in KW.

[3] What are the various losses occur in the transformer [Dec-04, May-2013]

1. Hysteresis losses
2. Eddy current losses
3. Copper Losses

[4] Why is the efficiency of transformers more than that of other rotating machines? [May-03]

• There are no moving parts in transformer.
• So the friction and mechanical losses are absent in the transformer.
• Thus the efficiency of the transformer is more than that of other rotating machines.

[5] How can the eddy current loss be reduced? [May-04]

• By using the laminated construction, the eddy current loss can be reduced.
• The path of the eddy currents is broken due to the insulating sheets kept between the laminations.
• This prevents the flow of eddy currents through the core and reduces the eddy current losses.

[6] How are sledging in transformer oil caused? [June -2006]

• While heating if the oil is exposed to oxygen then the reaction takes place.
• Because of this large deposits of dark and heavy material are formed in the oil.
• It is known as sledging of oil.
• These deposits can clog the cooling ducts.
• The sledging is happening due to decomposition of oil with long-term and continuous use.

[7] What are the properties of the oil used in the transformer? [Dec-2005]
The oil used in the transformer should have the following properties

1. Good conductor of heat
2. High coefficient of volume expansion
3. High insulating strength
4. Free from impurities like alkalies, sulphur etc
5. Free from moisture content

[8] Define voltage regulation of the transformer? [Dec-03]
The regulation is defined as change in the magnitude of the secondary terminal voltage, when full load ie, rated load of specified power factor supplied at rated voltage is reduced to no load, with primary voltage maintained constant expressed as the percentage of the rated terminal voltage.

[9] Define leakage inductance(Nov-02)
Inductance provided by the winding due to the leakage flux associated with it is called leakage inductance. It is the ratio of leakage flux linkages with the winding to the current passing through the winding.

[10] What is mean by leakage flux?(May 2011)
Part of primary flux and secondary flux completes the path through air and links with the respected bindings only. Such flux is known as leakage flux. These fluxes link with respective windings only and not to both the windings.

[11] What material is used in the transformer core? (Nov - 02)
High grade silicon steel laminations are used for the construction of the core.