Dr.A.P.J.Abdul Kalam University BE VII SEM ALL BRANCH Electrical Machines – III [EX-703] Dec - 2020 Question Paper

Dr.A.P.J.Abdul Kalam University

Bachelor of Engineering

Seventh Semester Main Examination, Dec-2020

Electrical Machines – III [EX-703]

Branch: EX

Time: 3:00 Hrs Max Marks 70

Page [3]

Note : 1. Attempt any five questions out of eight.

2. All question carry equal marks.

Q.1 (a) Write a short note on integral slots and fractional slot winding.

(b) What do you understand by winding factor? Explain in detail?

Q.2 (a) Derive the EM.F. equation of synchronous machine?

(b) A50 Hz,3-Ø, star connected alternator which generates 10000V between lines on open circuit, has a

flux per pole of 15× wb. If the distribution factor of the full pitch coil is .96.Find the number of

armature conductor in series per phase?

Q.3 (a) Explain in details the methods for suppression of harmonics in synchronous generators?

(b)What is armature reaction? Explain the effect of armature reaction in synchronous generator? (with

necessary diagram).

Q.4 (a) Draw the phasor diagrams for inductive, resistive and capacitive loads. With suitable emf equations.

(b) Determine the regulation of a 2kv single phase alternator, delivering a current

of100A at 0.8 pf leading.

Test result: full load current of 100 A is produced on short circuit by a field excitation of 2.5A. An emf of

500V is produced on open circuit by the same field current. The armature resistance is 0.8Ω.

Q.5 (a) Determine voltage regulation by (any one)

i) M.M.F method

ii) Potier’s triangle Method

(b) What is the use of synchronous Impedance method. Explain?

Q.6 (a) A 3-phase, Star connected,1000kva,11000V alternator has rated current of 52.5A. The ac resistance of the winding per phase is 0.45Ω OC test: field current=12.5A, voltage between lines =422V SC test: field current=12.5A, line current =52.5A Determine the full load voltage regulation of the generator at 0.8pf lagging.

(b) Explain two reactance theory for salient poles synchronous machines?

Q.7 (a) A 5kva, 220V, star connected 3-phase salient pole alternator with direct and quadrature axis reactance

of 12Ω and 7Ω respectively, delivers full load current at unity power factor. Calculate the excitation

voltage, neglecting resistance.

(b) Determine sub-transient, transient and steady state reactance?

Q.8 (a) What is the need for parallel operation of synchronous generator?

(b) Explain the principle of operation for synchronous motor?

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