Download AKTU B-Tech 7th Sem 2016-2017 NEN 701NEE 701 Electric Drives Question Paper

Download AKTU (Dr. A.P.J. Abdul Kalam Technical University (AKTU), formerly Uttar Pradesh Technical University (UPTU) B-Tech 7th Semester (Seventh Semester) 2016-2017 NEN 701NEE 701 Electric Drives Question Paper

Printed Pages: 4 NEN 701/NEE 701
? (Following Paper ID and Roll No. to be ?lled In your
' ' Answer Books) ?
Roll No.
B.TECH.
Regular Theory Examin?tion(0dd Sem-VlI), 2016-17
' ELECTRIC DRIVES
Time : 3 Hours Max. Marks : 100
Section - A
l Attempt all parts bf the following : (10X2=2i0).
a) What is meant by the naturepf load torque?
b) - What are the disadvantages of dc drives?
c) Classify various mechanical loads on the basis of
their torque-speed characteristics. i
d) Explain why the characteristics Ofa dc series motor
? is 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) 011 what factors does the rate of rise oftemperature '
dep end?
h) Why the thyristor control is preferred over Ward
Leonard system of speed control?
701/12/2016/2940 (1) [P.T.O.

10.
NEN 701/NEE 701
A30 kW, 400V, 3 ? (j), 4?PQle, 50 Hz induction motor has
full?load slip 0t?5%. lflhe ratio Ofstandstill reactance to
resistance per rotor phase is 4, estimate the plugging
torque at full speed.
I
Discuss Static Rotor Resistance Control 01? Induction
motor with suitable circuit diagram.
Describe the construction and principle ofoperation of ?
a switched reluctance n10t0r(SRM).
Explain the chopper control techniques for separately
excited dc motor under different modes of operation.
Explain the Operatioh of 1 - (l) halfcontrolled redti?er
fed separately excited dc. motor under continuous and
discontinuous modes of operation. Write the
nmthematical expression and draw speed characteristics
for different delay angles.
I Section - C
Attempt any two questions from this section
? (2x15=30)
Draw the torque?speed characteristics of an induction
motor with constant V/fcontrol for speed variation from
vety 10w up to the base speed. Also describe an open loop
scheme for Induction motor with \/?_I'fcohtrol.
701/12/2016/2940 (3) [pitcx
701/12/2016/?2940 (2)
' NEN 701/NEE 701
1) Suggest suitable motors for textile and paper mill
drive applications. ?
'j) Why the cooling time constant of a rotating machine
is usually larger than its heating time constant?
Section - B
Attempt any ?ve questions from this section. ;
(5x1q?=50)
Derive the relationship between the variatitm of
electromagnetic torque and load torque with tesp?lect to
speed for a stable operation of an electric drive. iWhat
are the drawbacks ofsteady state stability over, trailsient
stability? .
A drive has following equations for motor and! load
!
torques : T=(1+2a)m) & I; =3./a)?,,
Obtain the equilibrium points and determine their st?ady-
state stability. i
A 23 O V, 870 rpm, 100 A separately excited dc mot?r has
an armature resistance of 0.05 ohm. It is coupledfto an
overhauling load with a torque of400 N-m. Detefrmine
I
the speed at which motor can hold the load by regenerative
braking. .. I ?

11.
12.
NEN 701/NEE 701
A44OV, 50 Hz, 6?pole, Y?cdnnected wound rotor motor
has the following parameters :
R5 : 05 (2? R t Z 0493 X5: ?X j : 12(2? )(III 2 50 fl
Stator t0 rotor turn ratio is 3.5.
Motor is controlled by static rotor resistance control.
External resistance is chosen such that the breakdown
torque is produced at standstill for a duty ratio ofzem.
Calwlatc the value ol?externzll resistance; How duty ratio'
should be varied with Speed 30 that the 111010; accelerates
at maximum torque.
Discuss static Scherbius scheme for speed control 01"3 ?
slip ring induction motor. Draw a neat circuit diagram at:
the complete scheme. Mention one main advamtages 01?
?
this scheme compared to rotor resistance control.
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701/12/2016/2940 - (4)
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