Download AKTU (Dr. A.P.J. Abdul Kalam Technical University (AKTU), formerly Uttar Pradesh Technical University (UPTU) B-Tech 7th Semester (Seventh Semester) 2018-2019 NEN 701 Electric Drives Question Paper
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BTECH
(SEM Vll) THEORY EXAMINATION 2018-19
ELECTRIC DRIVES
Time: 3 Hours Total Marks:100
Notes: Assume any Missing Data.
SECTION ? A
1. Attempt all parts of the following. (10"2=20)
(a) What IS meant by the nature of load torque?
(b) What are the disadvantages of dc drives?
(c) Classify various mechanical loads on the basis of their torque-speed characteristics.
(d) Explain why the characteristics of a dc series motor are suitable for traction applications?
(e) What are the advantages and disadvantages of electrical braking?
(1') What are the problems faced in case a motor of wrong rating is chosen?
(g) On what factors does the rate of rise of temperature depend?
(h) Why the thyristor c0ntrol is preferred over Ward Leonard system of speed control?
(i) Suggest suitable motors for textile and paper mill drive applications.
0) Why the cooling time constant of a rotating machine is usually?larger than its heating
time constant? 5;.-
SECTION - B
2. Attempt any three parts of the following: . (3"IO=30)
(a) Draw the block diagram ofan electric drive. Explain the function ofPowcr modulator in detail.
(b) State the advantages ofdrive system. Give some applications with suitable drive system.
(c) Explain the Load equalization in drive.
(d) Illustrate the Dynamics of motor load system Also give comparison between DC and AC Drive.
(e) Elucidate the multi-quadrant operation of Electric drive system.
3.
SECTION - C
Note: - All questions are compulsory. (5*10?0)
Attempt any one parts of the following:
(3) Describe in detail the various components of load torque.
(h) A 6-pole, 50Hz, 3-phase wound rotor induction motor has ?ywheel coupled to its shaft. The total
moment of inertia of motor -load ??ywheel is lOOOkg-m2 of lOsec duration followed by a no
load period which is long enough for the drive to reach its no load speed. Motor has a slip of 3%
at a torque of SOON-m. Calculate (i) Maximum torque developed by the motor (ii) speed at the
end of declaration period. Assume motor speed? torque curve to be stmight line in the operating
range.
Attempt any one parts of the following:
(3) Explain chopper controlled DC motor drive.
(b) A 500kw, 3-phase, 3.3kV, SOHZ. 0.8(lagging) power factor ,4 pole, star connected synchronous
motor has following parameters: X.=lSQ, R.=0. Rated ?eld current is IOA. Calculate (i)
Armature current and power factor at half the rated torque and rated ?eld current (ii) Field current
to get unity power factor at the rated torque.
Attempt any one parts of the following:
(a) A 220 volts, 1500 rpm, 10 Amps separately excited dc motor has an armature resistance
of IO 0. It is fed from a single phase fully controlled bridge recti?er with an ac source
voltage of 230 volts, at 50 Hz. Assumingeontinuous load current, compute
i. The motor speed at ?ring angleof 30 degrees and torque of 5 NM
ii. Developed torque at the firingrangle of 45 degrees and speed of 1000 RPM
(b) Explain the various methods of braking can be applied to induction motor. And also state
what kind of braking is mote effective, justify, it.
Attempt any one parts of the following:
(c) Explain how the Static Scherbius drive is used in slip power recovery scheme.
(d) Describe in detail about speed control of self controlled synehronous motor drives,
Attempt any one parts of the following:
(a) Elucidate the operation of Brushless dc motor drive in detail.
(b) A 200 volts, 875 rpm, 150 A separately excited DC motor has an armature resistance of
0.06 Q. It is fed from a single phase ?llly controlled recti?er with an ac source of 220
Volts, 50Hz. Assuming continuous cotiduction calculate
i. F iring angle for rated motor torque iand 750 rpm
ii. Motor speed for u =16O degrees and rated torque
This post was last modified on 29 January 2020