Assignment-2 (1-March. 2017) Quiz1: 8-March 2017onwards

1. A 1000 kVA, 6.6 kV, 3 phase star connected synchronous generator has

a synchronous impedance of 6+j28 Ω per phase. It supplies full load

current of 0.75 lagging p.f. at rated terminal voltage. Compute the

terminal voltage for the same excitation when the generator supplies

full load current at 0.75 leading p.f. Draw the relevant phasor diagram.

2. A 3 phase, 6.6 kV, 50 Hz star connected alternator gave the following

readings during OC test. A field current of 2 A circulated rated armature

current of 313 A during short circuit test. Given the armature resistance

as 0.25 Ω per phase, determine the voltage regulation of the Alternator

when supplying (a) full load at 0.9 pf lagging (b) full load 0.9pf leading

by EMF method.

3. For the data given in Q3, determine the voltage regulation when

supplying ¾ th load at 0.7 p.f lead by MMF method

4. A 10 kVA, 440 V, 50 Hz 3 phase alternator has OCC given below

MANIPAL INSTITUTE OF TECHNOLOGY (A Constituent Institute of MANIPAL UNIVERSITY)

Department of Electrical and Electronics Engineering MANIPAL - 576 104, Karnataka, India

Electrical Machinery-II [ELE-2202]

ELECTRICAL MACHINERY-II [ELE 2202]

An excitation of 14 A was found to produce rated terminal voltage at

full load current and at zero p.f. and on short circuit 4 A excitation was

required to circulate full load current. Calculate the % regulation for full

load 0.75 p.f. (a) lag and (b) lead.

5. A 3 phase, 50 Hz, 10 Pole, star connected alternator has a spatial flux

density distribution given by B= 1.1 Sin θ + 0.6 Sin 3θ Tesla. The

machine has 2 slots per pole per phase and 4 conductors per slot. The

coil span is 1500, the coils being connected in 600 phase spread groups.

The armature diameter and axial core length are 125 cm and 45 cm

respectively. Calculate (i) pitch and distribution factors of fundamental

and third harmonic (ii) instantaneous emf per conductor (iii) RMS

values of phase and line induced emfs. (Assume фav = 0.64*фmax)

(Phase Spread=mβ)