Imp Questions Ed

IMPORTANT QUESTIONS IN ELECTRICAL
DRIVE
Unit -1
1 What is Electrical Drives? Explain it in terms of power modulator with suitable block
diagram?
2 Describe the main factor for deciding the choice of electrical drive for any applications?
3 Draw the block diagram and state the modes of operation of electrical drive.
4 Explain the classes of motor duty and how to determine motor rating for a particular load.
5 Derive the loads with rotational motor & loads with translational motion. What are the
component of load torque ?
Unit-2
1 Why DC series motor is suitable for torque overload condition compare to other DC motors?
2 Explain constant torque and constant power for dc drive?
3 Explain with drawing of speed-torque characteristic of dc separately excited motor during
regenerative & dynamic braking?
4 Explain operation of single phase semi-controlled & full control converter fed separately
excited dc motor? Also derive their voltage equation for converter output.
5 A 230V, 750rpm 25A dc series motor is driving at rated condition a load whose torque is
proportional to speed squared. The combined resistance of armature and field is 1Ω
calculate the motor terminal voltage and current for a speed of 400rpm. State the
assumption made for solving this problem.
6 A 200V, 875 RPM, 150A, Seperately excited dc motor has armature resistance 0.06Ώ. It is fed
from single phase fully controlled rectifier with an ac source voltage of 220V, 50Hz, Assuming
continuous condution. Calculate
(i) Firing angle for rated motor torque and 750 rpm
(ii) Firing angle for rated motor torque and -550 rpm
(iii) Motor speed for α = 160o and rated torque
7 What is dual converter? Explain multi-quadrant operation of a separately excited DC motor
drive fed from a dual converter in detail.
8 A 220V, 1500rpm, 50A separately excited DC motor with armature resistance of 0.5Ω is fed
from a circulating current dual converter with 3φ ac source voltage of 165V (line). Determine
converter firing angles for the following operating points.
i) Motoring operation at rated motor torque and 1000 rpm.
ii) ii) Braking operation at rated motor torque and –1000 rpm.
9 Explain operation of three phase semi-controlled & full control converter fed separately
excited dc motor with the help of their wavform? Also derive their voltage equation for
converter output.
Unit-3
1 Draw the torque-slip characteristic of 3-phase induction motor & also explain how VSI or
cyclo-converter control the speed on 3-phase induction motor with suitable block diagram.
2 Describe the slip power recovery in 3-phaser induction motor with suitable circuit diagram of
static scherbius drive or static Kramer driver scheme.
3 Draw the circuit diagram for VSI & CSI fed induction motor & compare their operation.
By Vijay Kumar Dubey, Asst. Professor (Department of Electrical Engineering, PIEMR-Indore)

4 Discuss variable frequency control of IM drive. Draw the relevant speed torque
characteristics and derive the mathematical expression showing the relationship of max
torque and operating frequency
5 Show that a variable frequency induction motor drive develops at all frequencies the same
torque for a given slip-speed when operating at constant flux.
6 How do you explain the operation of an induction motor speed control using rotor resistance
variation?
7 What are different methods of speed control of induction motor ? Also explain AC voltage
controller for delta connected Induction motor?
8 Explain the effect on performance on three phase induction motor with suitable equations if
(i) it is fed from Unbalanced voltage source
(ii) it is fed from inverter with effect of harmonics in line voltage
Unit-4
1 Why synchronous motor doesn’t have starting torque & how a salient pole synchronous
motor pull into synchronism before dc excitation when it is started on no load.
2 Explain true synchronous mode & self-synchronous mode with suitable close loop control of
synchronous motor?
3 Derive the Torque – Speed relation in Cylindrical rotor type & salient pole type synchronous
motor. If back EMF in synchronous reluctance motor is zero, so what will be the torque-
speed relation in Synchronous motor?
4 Write the difference between PMAC & PMBLDC motor. How PMBLDC Motor works using VSI,
Draw its circuit diagram & explain the operation with VSI.
5 Draw the circuit for low cost BLDC motor drives, explain its operation with suitable
waveform.
Unit-5
1 What is traction drive? Explain 25KV ac traction using semiconductor conveter controlled dc
motors?
2 Draw the circuit diagram for following
(i) A typical thyrister converter controlled dc motor drive system
(ii) A typical GTO inverter controlled induction motor drive
3 What is duty cycle of traction drive? How load sharing is achieved between Traction Motors?
4 How stepper motor works? Explain its important features. Draw the circuit diagram for
Unipolar drive for variable reluctance motor & Bipolar drive for permanent magnet & Hybrid
motor?
By Vijay Kumar Dubey, Asst. Professor (Department of Electrical Engineering, PIEMR-Indore)

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IMPORTANT QUESTIONS IN ELECTRICAL

By Vijay Kumar Dubey, Asst. Professor (Department of Electrical Engineering, PIEMR-Indore)

By Vijay Kumar Dubey, Asst. Professor (Department of Electrical Engineering, PIEMR-Indore)

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