Electrical Machines I

Explain, what does fingers and thumb represents in Fleming right hand rule?

Give application of Biot Savart Law.

Give name of sources that store energy in magnetic circuits.

Give example of linear and non-linear magnetic circuits.

What is an air gap flux?

Give similarity between lap and wave winding.

Give name of losses related to DC motors.

What are output of back to back test of DC machines?

What do you understand by the term ‘Flux per pole’?

What are the basic units of a 3-phase transformer?

Explain, why all electrical machines, when operating develops torque and generates voltage at the same time?

Explain, how B-H curves are determine for magnetic materials? Also, explain its application.

Explain, how derivation of back EMF equation is determined?

A series motor has a resistance of 0.5 ohm between the terminals. It runs at a speed of 1500 r.p.m. when taking 10 A from 200 V supply. Find the speed, at which it will run when taking 20 A from the same supply? Assume no saturation.

By the help of suitable diagram, explain the method of speed control through armature voltage.

Explain the phenomena of back EMF with armature reaction.

By the help of neat diagram, explain the working of an Auto transformer.

By the help of a neat diagram design and explain a DC machine with (a) separately excitation system (b) series exaction system.

(a) A 230 V DC shunt motor runs at 1000 rpm when the armature current is 35 A. The resistance of the armature circuit is 0.3 ohm. Calculate the addition resistance required in the armature circuit to reduce the speed of the motor to 750 rpm assuming the armature current is then 25 A. (b) A shunt motor supplied at 250 V runs at 900 rpm when the armature current is 30 A. The resistance of the armature circuit is 0.4 ohm. Calculate the resistance required in series with the armature to reduce the speed to 600 rpm. Assuming current is then 20 A.

Explain the working principle, construction and operation of a single phase transformer. Also, draw and explain its equivalent circuit with phase diagram.

Give basic construction mechanism of DC machine, also explain its magnetic structure and air gap flux density distribution.

Write Short note on - (a) Ampere Law (b) Biot Savart Law