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Posted Date: 26 Jan 2009 Posted By: ravikanth Member Level: Diamond
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2008 Jawaharlal Nehru Technological University Electrical and Electronics Engineering IV B.Tech I Semester Regular Examinations, November 2008 POWER SEMICONDUCTOR DRIVES Question paper
Code No: R05410202 Set No. 4
IV B.Tech I Semester Regular Examinations, November 2008
POWER SEMICONDUCTOR DRIVES
(Electrical & Electronic Engineering)
Time: 3 hours Max Marks: 80
Answer any FIVE Questions
All Questions carry equal marks
? ? ? ? ?
1. Derive the Speed, Torque Equations of a fully controlled converter connected to
separately excited D.C motor with continuous current operation with necessary
waveforms. [16]
2. Explain the Speed - torque Characteristics of a separately excited dc motor con-
nected to a three phase semi controlled converter. [16]
3. (a) With neat circuit diagram and waveforms, explain dynamic braking of sepa-
rately excited motor by single phase converter.
(b) A dc shunt motor has the armature resistance of 0.04
and the field winding
resistance of 10
. Motor is coupled to an over hauling load with a torque of
400N-m. Following magnetization curve was measured at 600 rpm:
Field Current, A 2.5 5 7.5 10 12.5 1.5 17.5 20 22.5 25
Back emf, V 25 50 73.5 90 102.5 110 116 121 125 129
Calculate the value of RB when the motor is required to hold overhauling load
at 1200rpm. [8+8]
4. A 220V, 70A D.C series motor has combined resistance of armature and field is 0.12
ohms running on no-load with the field winding connected to a separate source. It
gave following magnetization characteristics at 600 rpm
FieldCurrent(A) 10 20 30 40 50 60 70 80
TerminalVoltage (V) 64 118 150 170 184 194 202 210
Motor is controlled by a chopper with source voltage equal to 220V. calculate
(a) Motor Speed for a duty ratio of 0.6 and motor current of 60A
(b) Torque for a speed of 400 rpm and duty ratio of 0.65. [16]
5. Draw the following AC voltage controllers for varying the speed of a 3 phase In-
duction motor
(a) Star connected controller
(b) Delta connected controller
(c) Delta connected Stator and controller.
Discuss in detail about the above types of controllers. [16]
6. With neat block diagrams explain closed loop operation of Induction motor drives.
7. (a) Why rotor resistance control is preferred in low power crane drives?
(b) What are the advantages of static rotor resistance control over conventional
method of rotor resistance control? Explain its principle of operation with
suitable circuit diagrams and characteristics. [8+8]
8. (a) What is a self control mode of Synchronous motor?
(b) Draw and explain the block diagram of a self controlled synchronous motor
fed from a three phase inverter.
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