EET 202 DC MACHINES AND TRANSFORMERS

DC motor back emf, generation of torque

torque equation, performance characteristics

Starting of dc motors,3point and 4 point starters

Speed control of dc motors , field control, armature control

Braking of dc motors

Power flow diagram , losses and efficiency

Testing of dc motors – Swinburne’s test, Hopkinson’s test, and retardation test

DC motor applications

Retardation test

Construction

Armature winding

Types of armature winding

Single phase transformers –constructional details, principle of operation, EMF equation

ideal transformer, dot convention, magnetising current, transformation ratio, phasor diagram

operation on no load and on load, equivalent circuit, percentage and per unit impedance, voltage regulation.

Transformer losses and efficiency, condition for maximum efficiency, kVA rating.

Testing of transformers– polarity test, open circuit test, short circuit test, Sumpner’s test

separation of losses, all day efficiency. Parallel operation of single-phase transformers– numerical problems

Condition for maximum voltage regulation

Autotransformer – saving of copper –rating of autotransformers

Numerical problems- Autotransformer

Tap changing transformers – no load tap changing, on load tap changing, dry type transformers.

Three phase transformer – construction

Different connections of 3-phase transformers