THAPAR INSTITUTE OF ENGINEERING & TECHNOLOGY PATIALA
DEPARTMENT OF ELECTRICAL AND INSTRUMENATION ENGINEERING
UEE306 Electro-Mechanical Energy Conversion
TUTORIAL 3
(Basic Performance Equation for D.C. Machines, Magnetization Curve, Operating
Characteristics of Separately Excited and Shunt D.C. Generators)
Course Instructors: Dr. Prasenjit Basak & Dr. Amit Kumar
Q1. A 250 V, 10 kW D.C. shunt generator has 1400 turns on each pole. At rated speed, a shunt
field current of 2 A produces a no-load voltage of 250 V, but at rated load the same load voltage
of 250 V can be produced by a field current of 2.2 A. It is required, not to change the field
current for maintaining load voltage constant, but add a series field winding. Calculate the
number of series field turns per pole required for long shunt connection.
[Series field turns required = 7]
Q2. A separately excited generator, when running at 1200 RPM supplies 200 A at 125 V to a
circuit of constant resistance. What will be the current when the speed is dropped to 1000 RPM
if the field current is unaltered? Armature resistance is 0.04 Ω, total drop at brushes 2 V, ignore
change in armature reaction. [166 A]
Q3. A 4-pole shunt generator with lap-connected armature having field and armature
resistances of 50 Ω and 0.1 Ω respectively supplies 60 numbers 100 V, 40 W lamps. Calculate
the total armature current, the current per armature path and the generated emf. Allow a
constant drop of 1 V per brush. [26 A, 6.5 A, 104.6 V]
Q4. The following data pertain to the magnetization curve of a DC shunt generator at 1500
rpm.
If (A)
0
0.4
0.8
1.20
1.60
2.00
2.40
2.80
3.00
Ea (V)
6
60
120
172.5
202.5
221
231
237
240
For this generator, obtain:
(a) the voltage on open circuit to which the machine will build up (i.e. no-load emf) for a
total shunt filed resistance of 100 Ω;
(b) the critical value of shunt field resistance at 1500 rpm;
(c) the critical speed for the shunt filed resistance of 100 Ω;
(d) the magnetization curve at 1200 rpm and therefore the open circuit voltage for a field
resistance of 100 Ω;
(e) the terminal voltage of the generator if the total armature resistance is 0.3 Ω, armature
current is 50 A and the speed is 1500 rpm. Neglect armature reaction.
[(a) 230 V; (b) 150 Ω; (c) 1000 rpm; (d) 165 V (e) 207 V]
