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AC / DC Motor Drives

Electrician Trade Theory, Module-9

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By Roni
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AC / DC Motor Drives


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Q1: Which control system consumes very low power for motion control in AC and DC motors?

  • Field control
  • Drives control
  • Voltage control
  • Armature control

Q2: Which drive is classified according to mode of operation?

  • Group drive
  • Manual drive
  • Individual drive
  • Continuous duty drive

Q3: What is the name of the characteristic curve in D.C drive?

characteristic curve in D.C drive

  • Speed Vs torque characteristic
  • Torque Vs field current characteristic
  • Speed Vs armature current characteristic
  • Field current Vs armature current characteristic

Q4: What is the name of the component marked as 'X' in the block diagram of AC drive?

block diagram of AC drive component X

  • Rectifier
  • D.C bus
  • Inverter
  • A.C motor

Q5: What is electric drive?

  • A device used as prime mover for generator
  • A device converts A.C to D.C supply
  • An electro mechanical device for controlling motor
  • A machine converts mechanical energy into electrical

Q6: What is the full form of B.O.P in D.C drive?

  • Bridge Operation Panel
  • Basic Operational Panel
  • Basic Operation Programme
  • Bridge Operator Programme

Q7: Which is the classification of drive according to dynamics and transients?

  • Short time duty drive
  • Intermittent duty drive
  • Automatic control drive
  • Variable position control drive

Q8: What is the function of power controller in drive circuits?

  • It sounds an alarm in no load conditions
  • It detects the overloading condition of motor
  • It reduce motor current during transient operation
  • It maintain the torque at low voltage conditions

Q9: Why it is necessary to keep V/F ratio constant in a drive?

  • Keep the stator flux maximum
  • Maintain the rotor current minimum
  • Maintain the speed of motor constant
  • Maintain the rated torque at all speeds

Q10: Which power modulator used in the electric drive system?

  • Cyclo converters
  • Frequency multiplier
  • Phase sequence indicator
  • Servo controlled voltage stabilizer

Q11: Which type of sensing unit employed in drive system?

  • Opto coupler
  • Speed sensing
  • Photo voltaic cell
  • Resistance temperature detector

Q12: Which type of machine in industries is provided with multi motor electric drive?

  • Rolling machine
  • Air Compressor
  • Shearing machine
  • Heavy duty electric drilling machine

Q13: Which control system is used for Eddy current drives?

  • Slip controller
  • Rectifier controller
  • AC voltage controller
  • DC chopper controller

Q14: What is the purpose of JOG key in control panel of D.C drive?

  • Stop the motor
  • Restart the motor
  • Inching operation
  • Reverse the direction of motor

Q15: What is the purpose of LCD on basic operator panel in D.C drive?

  • Indicate the fault
  • Display the speed
  • Monitor the parameter
  • Display availability of supply

Q16: What is the reason of using shielded cable for connecting low level signal circuits in DC drives?

  • Easy for connection
  • Good appearance
  • Protects from mechanical injuries
  • Eliminates the electrical interference

Q17: Which device controls the speed of A.C motor in A.C drive?

  • Field supply unit (FSU)
  • COMMS technology box
  • Speed feedback technology box
  • Microprocessor based electronic device

Q18: What is the main use of A.C drive?

  • High starting torque
  • Group drive motors
  • Control stepless speed in motors
  • Interlocking system in Industries

Q19: What is the function of IGBT in AC drive?

  • Smoothening incoming A.C supply
  • Controls the power delivered to the motor
  • Stabilize the output voltage from the rectifier
  • Converts incoming A.C power into D.C power output

Q20: Why the A.C drives are better suited for high speed operation?

  • High starting torque
  • Robust in construction
  • Having lighter gauge winding
  • No brushes and commutation

Q21: What is the advantage of AC drive compared to DC drive?

  • Requires less space
  • Installation and running cost is less
  • Fast response and wide speed range of control
  • Power circuit and control circuits are simple

Q22: Which is the application of single quadrant loads operating in first quadrant in drives?

  • Hoists
  • Elevators
  • Conveyors
  • Centrifugal pumps

Q23: What is the function of Field Supply Unit (FSU) in DC drive?

  • Produces required firing current to the firing circuit
  • Provides variable voltage to the field winding of motor
  • Provides a constant voltage to the field winding of motor
  • Provides a constant voltage to the armature of the motor

Q24: What is the disadvantage of DC drive?

  • Not suitable for high speed operation
  • More complex with a single power conversion
  • More expensive than AC drive for high capacity motor
  • Installation of DC drives is more complicated

Q25: What is the purpose of LCD in Basic Operator Panel (BOP) in AC drive?

  • Indicate the status of drive
  • Monitor the parameter of AC drive
  • Indicate the display error in reading
  • Indicate the incorrect operation of BOP

Q26: Which is the correct sequence operation of key button in BOP of AC drive to change the direction of rotation?

  • Press ON REV ON
  • Press OFF REV ON
  • Press ON OFF REV ON
  • Press ON REV OFF ON

Q27: What is the purpose of PROG/DATA button in BOP of AC drive?

  • To change the parameter setting
  • To store the entered data and factory stored data
  • To display the data direction of rotation forward/REV
  • To display the data status of frequency and current

Q28: Which is proportional to the torque in D.C motor?

  • Back e.m.f
  • Field current
  • Terminal voltage
  • Armature current

Q29: What is IGBT in VF drive?

  • Inverter switching device
  • D.C bus switching device
  • Rectifier switching device
  • Field supply switching device

Q30: What is the function of VSI drives?

  • Converts A.C to D.C
  • Converts A.C to A.C
  • Converts D.C to A.C
  • Converts D.C to D.C

Q31: Why the A.C drives are mostly used in process plant?

  • Easy to operate
  • Robust in construction
  • Very high starting torque
  • Maintenance free long life

Q32: How the base speed of D.C shunt motor can be increased by using D.C drive?

  • By reducing the field current
  • By increasing the field current
  • By increasing the supply voltage
  • By reducing the armature voltage

Q33: How the constant torque can be obtained from armature and field controlled drives?

  • By reducing the field current
  • By increasing the field current
  • By reducing the armature current
  • By controlling the armature voltage
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2nd year, Trade Theory
Theory ITI
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