Electrical Drives And Controls Set 12

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This set of Electrical Drives and Controls EDC Multiple Choice Questions & Answers (MCQs) focuses on Electrical Drives And Controls Set 12

Q1 | Thyristor controlled starter is preferred over DOL starter due to                    
  • lesser losses
  • controlled direction
  • least resistance offered
  • all of the mentioned
Q2 | For a 7.46 kW, 200 V dc shunt motor with full load efficiency of 85% has armature resistance of 0.25 ohms. Calculate the value of starting resistance in ohms for a current 1.5 times of the full load current.
  • 2.788
  • 3.038
  • 2.688
  • 2.588
Q3 | The effect of fringing increases as we
  • increase air gap
  • decrease air gap
  • increase in flux density
  • introduce more ferric core material
Q4 | The post effects of the armature reaction is                    
  • main field distortion
  • shift in mna
  • reduction in main field
  • none of the mentioned
Q5 | If the students give a forward shift of 10° to the dc generator, then it                    
  • reduces flux per pole
  • improves flux per pole
  • increases the flux density in core
  • none of the mentioned
Q6 | A dc machine is run at rated speed in forward direction and then in backward direction. It is observed that, speeds of the rotation are different, then it leads to the conclusion of                    
  • incorrect brush placement
  • incorrect pole and core alignment
  • incorrect field supply
  • all of the mentioned
Q7 | For a dc machine, its commutator has a diameter of 50 c rotating at 1000 rpm. For a brush width of 1 cm, the time commutation taken by the machine will be                    
  • 0.382 ms
  • 0.456 ms
  • 0.573 ms
  • 0.312 ms
Q8 | An induction motor can be said analogous to                    
  • transformer
  • synchronous motor
  • universal motor
  • stepper motor
Q9 | A 3-phase induction motor with its rotor blocked behaves similar to a                    
  • transformer under short circuit of secondary terminals
  • transformer under open circuit of secondary
  • synchronous motor under slip test
  • synchronous motor under open circuit
Q10 | No load current in induction motor is 10- 20% of full load current and the no load current of transformer is 2-6%.
  • true
  • false
Q11 | The no load current of the transformer is very less due to                    
  • mutual flux having low reluctance iron core
  • mutual flux having high reluctance iron core
  • leakage flux having low reluctance iron core
  • leakage flux having high reluctance iron core
Q12 | The no load current of the induction motor is high due to                    
  • long and high reluctance path between stator and rotor
  • mutual flux having moderate reluctance path between stator and rotor
  • leakage flux having low reluctance iron core
  • leakage flux having high reluctance iron core
Q13 | At no load induction motor has possible power factor as                    
  • 0.2
  • 0.5
  • 0.65
Q14 | Mechanically air gaps in induction motor are kept very low to avoid                    
  • lower power factor
  • lagging nature
  • magnetizing current
  • all of the mentioned
Q15 | The low no load power factor                    
  • reduces full load operating pf
  • increases full load operating pf
  • reduces full load excitation voltage
  • increases full load excitation voltage
Q16 | An induction motor when started on load, it does not accelerate up to full speed but runs at 1/7th of the rated speed. The motor is said to be                    
  • locking
  • plumming
  • crawling
  • cogging
Q17 | The great advantage of the double squirrel-cage induction motor over single cage rotor is that its                    
  • efficiency is higher
  • power factor is higher
  • slip is larger
  • starting current is lower
Q18 | Ward-Leonard system of system of speed control is not recommended for                    
  • constant speed operation
  • wide speed
  • frequent-motor reversed
  • very slow speed
Q19 | Mark the wrong option. Which of the following cause and effect behaviour in speed control is correct when field resistance is increased.
  • decrease in flux
  • increase in armature current
  • increase in emf
  • decrease in speed
Q20 | At a very low speed, increase in field resistance will                    
  • decrease the speed of motor
  • increase the speed of motor
  • not have signicant effect on speed
  • no effect
Q21 | Small DC motors have best speed control by                    
  • armature voltage control
  • field resistance control
  • any of the methods
  • none of the mentioned
Q22 | To implement armature voltage control, it must be ensured that                    
  • it is used on separately excited machine
  • it is used on shunt machine
  • it is used on series machine
  • any of the mentioned machine
Q23 | The torque limit of speed for a shunt motor                    
  • remains constant till base speed
  • remains constant after base speed
  • varies linearly after base speed
  • varies inversely till base speed
Q24 | A laboratory group was working with a set of 3-hp shunt DC motor. But there was a mistake that it was fused with a 0.3A fuse instead 3A fuse. Then it was started
  • a flash occurred instantly
  • it ran for 3s and fuse was blown
  • it ran normal
  • none of the mentioned
Q25 | Run-away for large DC machine is avoided by using                    
  • a turn or two of cumulative compounding
  • compensating winding
  • stablizer winding
  • all of the mentioned