THAPAR INSTITUTE OF ENGINEERING & TECHNOLOGY PATIALA
DEPARTMENT OF ELECTRICAL AND INSTRUMENATION ENGINEERING
UEE306: Electro-Mechanical Energy Conversion
TUTORIAL 2 (Armature Reaction, Interpoles, Commutation)
Course Instructors: Dr. Prasenjit Basak & Dr. Amit Kumar
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Q1. A 6-pole, 148 A D.C. shunt generator has 480 conductors and is wave-wound. Its field
current is 2 A. Find the demagnetizing and cross-magnetizing ampere-turns per pole at full load
if (a) brushes are on GNA, (b) brushes are shifted from GNA by 5º electrical, (c) brushes are
shifted from GNA by 5º mechanical. [(a) 0 AT/pole, 3000 AT/ pole, (b) 166.67 AT/pole,
2833.33 AT/ pole, a) 500 AT/pole, 2500 AT/ pole]
Q2. A 4-pole, 100 kW, 200 V lap-connected D.C. machine has 256 conductors. Find the
number of turns required on each interpole, if interpolar air-gap is 1 cm and interpolar flux
density is 0.25 T. Neglect the effect of iron parts of the circuit and of the leakage.
[12 turns per pole]
Q3. A 2000 kW, 400V, 14-pole dc machine has a lap wound armature with 1100 conductors.
The pole arc to pole pitch ratio is 0.7. Compute the number of pole face conductors of the
compensating winding in each pole, so as to obtain uniform air-gap flux density under the pole
faces. [4 conductors per pole]
Q4. A compensated generator has 12000 armature ampere-turns per pole, the ratio (pole
arc/pole pitch) =0.7, the length of interpolar air-gap = 1.25 cm and the flux density in the
interpole air gap = 0.3 Wb/m2. Find the ampere turns per pole for the compensating winding
and for the interpole winding. [8400, 6600]
Q5. A commutator having a diameter of 76 cm rotates at 600 RPM. Find the approximate time
of commutation for brush width be 1.5 cm. [0.628 x 10-3 sec]
Q6. A single turn armature coil has, in the commutating zone, an inductance of 0.02 mH. Find
what commutating field is required for the straight-line commutation of 25 A.
[0.5 m-Wb]
Hints: L = Nφ/I
