Important RGPV Question
EX-801 Electrical Drives
VIII Sem, EX
UNIT 1-Basic Concepts Of Electric Drives
Q.1) What is the requirement of Electric Drives?
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Q.2) Discuss about constant power and constant torque drives.
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Q.3) What do you understand by rating of drives and how should be the selection of drives be done?
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Q.4) Discuss about the mechanical systems stability of electric drives.
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Q.5) Discuss about the referred moment of inertia and torque of motor load combination.
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Q.6) Explain about the different speed torque characteristics of different machines and give their utility in section for industrial loads.
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Q.7) Differentiate between two and four quadrant drives.
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Q.8) Explain briefly about the functions of different converters that are operated in block diagram of electrical Drives.
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Q.9) A motor equipped with a flywheel is to supply a load torque of 1000 N-m for 10 sec. followed by a light load period of300 N-m long enough for the flywheel to regain its steady state speed. It is desired to limit the motor torque to 700 N-m.What should be the moment of inertia of flywheel? Motor has an inertia of 10 Kg-m². Its no load speed is 500 rpm and the slip at a torque of 500 N-m is 5%. Assume speed torque characteristic of motor to be a straight line in the region of interest.
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Q.10) Explain that the steady-state stability of a drive depends on relative characteristics of the motor and load and not just on motor (or load) characteristic.
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Q.11) A drive has following equations for motor and load torques.
T=(1+2ωm) and Tt =3√ωm
Obtain the equilibrium points and determine their steady-state stability.
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UNIT 2-DC Drives Starting & Braking Of Conventional
Q.1) Give a brief review of AC and DC motors.
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Q.2) Discuss about phase, controlled and chopper controlled drives.
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Q.3) Discuss about Energy Recovery System.
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Q.4) Draw and explain the torque-speed characteristics for dynamic braking operation of D.C series motor. Why torque becomes zero at finale speed?
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Q.5) Define a DC chopper. Describe the various types of chopper configuration with necessary diagrams.
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Q.6) Sketch the appropriate voltage and current waveforms for firing angle 30° that is working with a single phase semi converter fed with DC series motor.
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Q.7) A 200V, 10.5 A, 2000 rpm shunt motor has the armature and field resistances of 0.5 and 400 respectively. It drives a load whose torque is constant at rated motor torque. Calculate motor speed if the source voltage drops to 175 V.
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Q.8) Field control is employed for getting speeds higher than rated and armature voltage control is employed for getting speeds less than rated. Why?
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Q.9) A 220 V, 1500 rpm separately excited dc motor has rated armature current of A. The armature resistance is 3 ohm. It is fed through fully controlled converter from a 220 V 50 Hz supply. Final firing angle of converter for half the rated torque at 600 rpm. Assume that torque is proportional to armature current.
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UNIT 3-Induction Motor Drives
Q.1) Discuss about conventional method of starting braking and speed control.
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Q.2) Discuss about current sources fed IM drives.
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Q.3) Explain about VSI and CSI fed synchronous motor drives
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Q.4) Explain about Self-Controlled-Brush less and commutator less DC and AC motor drives.
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Q.5) Explain with suitable block diagrams the various types of VSI controlled induction motor drives.
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Q.6) A 3-Phase 6-pole, 400 V, 970 rpm, 20 kW, 970 rpm, 50 Hz delta connected induction motor has rotor leakage impedance of stator impedance and rotational losses are assumed as negligible. If this motor is energized from a source of 3-phase, 400 V, 80 Hz, then compute
i) The motor speed at rated torque
ii) The slip at which maximum torque occurs
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Q.7) Explain the conventional Scherbius system with that of a Scherbius drive.
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Q.8) A wound rotor induction motor has full load speed of 288 rpm. The supply frequency in 50 Hz. Find
i) Number of poles
ii) Slip
iii) Slip for full load if rotor resistance is doubled
iv) New value of rotor copper loss if initial rotor copper loss is 275 W.
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Q.9) For variable frequency control of induction motor explain the following points
i) For speeds below base speed (V/f) ratio is maintained constant, why?
ii) For speeds above base speed, the terminal voltage is maintained constant, why?
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Q.10) A 3-phase induction motor takes 4 time full-load current on direct starting and develops 1.5 times full-load torque. What must be the applied voltage to obtain full-load torque at starting and what will be the starting current?
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UNIT 4-Synchronous Motors Drives VSI And CSI Fed
Q.1) Draw the block diagram of closed loop synchronous motor drive fed from VSI and explain.
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Q.2) Describe self controlled load commutated inverter, controlled synchronous motor drive in detail and compare them.
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Q.3) A 500 kW, 3-phase, 6.6 kV, 60 Hz, 6 pole Y-connected wound field synchronous motor has the following parameters: Xm=78Ω, Xs=3Ω, p.f=1, Nr=5, Rs=0 (negligible) the motor speed is controlled by variable frequency control with a constant V/f ratio up to base speed and rated terminal voltage above base speed. Calculate T, Pm, Im and If for the motor operation at rated armature current and upf. What is the range of constant power operation, neglect friction, windage and core loss.
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Q.4) Explain working of Voltage Source Inverter (VSI) fed synchronous motor drives.
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Q.5) A 3-phase, 400V, 50Hz, 4 pole star-connected reluctance motor with negligible armature resistance has and For a load torque of 80 Nm. Calculate:
i) The load angle
ii) The line current
iii) The input power factor
Neglect rotational losses.
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Q.6) When rotor speed is close to synchronous speed, application of dc field leads to pull-in of the rotor into synchronism. However, application of dc field at a speed considerably lower than synchronous speed does not lead to pull-in of the rotor into synchronism, why?
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UNIT 5-Special Drives
Q.1) Explain the fundamentals of switched reluctance motors.
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Q.2) Discuss about the digital control of drives.
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Q.3) Briefly describe how to control load angle in Stepper Motor.
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Q.4) Draw and explain digital control of drives.
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Extra Questions-
Q.1) Write short notes on any two of the followings.
i) Slip controlled 1M drives
ii) Crammers and Scherbius drives
iii) CNC
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Q.2) Write short notes on any two of the followings:
i) Group and individual drives
ii) CNC
iii) Energy recovery system
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Q.3) Write a short notes on (any two):
i) Constant power and constant torque drive
ii) Transient and steady state analysis of dc drives
iii) Scherbius induction drives
iv) Electric traction drives
(RGPV May 2024)
— Best of Luck for Exam —
