Gujarat Technological University 2011-7th Sem B.E Electrical Engineering Electrical Machines-3, - Question Paper

* Gujarat Technological university
* Electrical Machines-3
* 2011

Q-1(a) discuss Hopkinson test for determination of efficiency of DC shunt machine.[Mark 07]
(b) provide merits of connecting alternators in parallel. discuss three dark lamp method of synchronizing two 3-phase alternators.[Mark 07]

Q-2(a) define construction and working principle of reluctance motor.[Mark 07]
(b) A 3-phase , 8-pole,750 rpm star connected alternator has 72 slots on the armature. every slots has 12 conductors and winding is short chorded by two slots. obtain the induced emf ranging from lines, provided the flux per pole is 0.06Wb.[Mark 07]
*OR*
(b) discuss coil span factor and distribution factor of an alternator.

Q-3(a) Write short note on field test for DC series machine.[Mark 07]
(b) discuss construction and working principle of hystersis motor.[Mark 07]
*OR*
(a) two identical DC machines when tested by Hopkinson test gave subsequent results:

If= 2.5 & 2A. Vl=220V . Il including both field current is 10A. Motor armature current is 73 A.The armature resistance of every machines is 0.05 ohm. compute the efficiency of both machines.
(b) Write short note on AC servo motor.

Q-4(a) Briefly discuss the ZPF method of finding the voltage regulation of alternator.[Mark 07]
(b) What is the armature reaction ? discuss the effect of armature reaction on the terminal voltage of an alternator.[Mark 07]
*OR*

Q-4(a) elaborate the causes of harmonics in voltage waveform of alternator? How can these be minimized?
(b) discuss 2 reaction theory of salient pole synchronous machine.

Q-5(a) discuss an experimental method of determining 'V' curves for a synchronous motor.[Mark 07]
(b) Briefly discuss the principle of operation of DC servo motor and PM synchronous motor. [Mark 07]
*OR*

Q-5(a) discuss circle diagram of auto synchronous motor.
(b) 1) discuss various torques in synchronous motor.
2)Draw experimental setup diagram of Brake test for DC motor & write down its efficiency formula.

Earning:   Approval pending.