1)(a) describe with suitable sketches the construction of a DC machine.
(b) Deduce the EMF equation of DC generator.
2) Draw and describe no-load and load characteristics of DC shunt, series and compound generators.
3) Describe the effect of armature reaction in a DC shunt generator. How is its demagnetizing and cross-magnetizing ampere turns find outd?
4) Describe the process of commutation in a DC machine in detail.
5) With the help of a suitable circuit diagram, describe the procedure for paralleling two DC shunt generators and for transferring load from one machine to the other.
6) A 4-pole, 50 kW, 250 V, wave wound shunt generator has 400 armature conductors. Brushes are given a lead of 4 commutator segments. Compute the demagnetization ampere-turns per pole if shunt field resistance is 50 ohm. Also compute extra shunt field turns per pole to neutralize the demagnetization.
7) Describe the various methods used for speed control of D.C. shunt motor.
8) With the help of neat circuit diagram, describe swinburne’s test and deduce the relations for efficiency (both for generator and motor) also prepare down the merits and demerits of this method
9)(a) Describe about circuit model of D.C. machine in detail.
(b) A 440 V D.C shunt motor takes 4A at no load. Its armature and field resistances are 0.4 ohms and 220 ohms respectively. Evalyate the kW output and efficiency when the motor takes 60A on full load.
10)(a) Deduce the expression for torque developed in an armature of a D.C. motor.
11) With the help of neat circuit diagram, describe Hopkinson’s test and deduce the relations for efficiency (both for generator and motor) also prepare down the merits and demerits of this method.
12)a) Describe about different methods of excitation in detail.
(b) Deduce the expression for efficiency of D.C. machines.