Em Qb1.docx

CAMBRIDGE INSTITUTE OF TECHNOLOGY K.R. PURAM, BENGALURU-560036.

Department of Electrical and Electronics Engineering Subject name:

Electric Motors

Subject code:

17EE44

Semester: IV

QUESTION BANK FOR MODULE-1 Sl. No. 1.

2.

3.

4.

QUESTIONS

RBT Levels

Marks

a)

Draw a neat sketch of four point starter of dc shunt motor.

CO1

L1

04M

b)

Explain the characteristics of dc shunt motor. List its applications.

CO1

L2

05M

c)

A 230 V dc shunt motor runs at 800 rpm and takes armature current of 50 A. Determine the resistance to be added to the field circuit to increase speed from 800 rpm to 1000 rpm at an armature current of 80 A. Assume flux proportional to field current. Given armature resistance and field resistance to be 0.15  and 250  respectively.

CO1

L2

06M

a)

Give the symbolic representation of power flow in dc machines.

CO1

L1

04M

b)

Derive an expression for the torque in a dc motor.

CO1

L2

05M

c)

Explain the different methods of speed control of dc series motor with relevant circuit diagrams.

CO1

L2

06M

a)

Find the condition for maximum efficiency of a dc motor.

CO1

L1

04M

b)

Explain the characteristics of dc series motor. Mention its applications.

CO1

L2

05M

c)

Explain the operation of three point starter with a neat sketch.

CO1

L2

06M

a)

What is the necessity of starter for dc motors?

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L1

04M

b)

Explain the different methods of controlling speed of dc shunt motor with relevant circuit diagrams.

CO1

L2

05M

CO1

L2

06M

c)

5.

COs

A series motor with an unsaturated magnetic circuit and 0.5  total resistance, when running at certain speed takes 60 A at 500 V. If the load torque varies as the cube of the speed, determine the resistance required to reduce the speed by 25%.

a)

What is the action of no-volt coil in three point starter during supply failure?

CO1

L1

04M

b)

With a neat diagram, explain Ward Leonard method of speed control for dc shunt motor.

CO1

L2

05M

c)

6.

7.

A dc series motor of resistance 1.5  runs at 750 rpm at 220 V with a current of 20 A. Determine the speed at which it will run when connected in series with a 4.5  resistance and taking the same current.

06M CO1

L2

a)

How overload release in three point starter functions during overloading condition?

CO1

L1

04M

b)

What is back EMF ? Explain its significance in dc motor.

CO1

L2

05M

c)

A 4 pole dc shunt motor takes 22 A from 220 V supply. The armature and shunt field winding resistances are 0.5  and 100  respectively. The armature is lap connected with 300 conductors, if the flux/pole is 20m wb, determine the speed and torque developed.

CO1

L2

06M

a)

What are the advantages and limitations of four point starter?

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L1

04M

b)

Explain the various losses occurring in dc motor.

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L2

05M

A 10 kW, 250 V dc shunt motor with an armature resistance of 0.8  and a field resistance of 275  takes 3.91 A, when running light at rated voltage and rated speed. Determine the machine efficiency at rated voltage and speed as a

CO1

L2

06M

COs

RBT Levels

Marks

CO2

L1

04M

CO2

L2

05M

c) With a neat circuit diagram, explain the procedure of conducting Swinburne’s test on dc motor.

CO2

L2

06M

a) What are the advantages of back to back test over other tests?

CO2

L1

04M

CO2

L2

05M

CO2

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06M

c)

i. ii.

generator when delivering an output of 10 kW motor drawing an input of 10 kW.

QUESTION BANK FOR MODULE-2 Sl. No. 1.

QUESTIONS a) What are the advantages & disadvantages of Swinburne’s test? b) A 500 V, dc shunt motor when running on no load takes 5 A. Armature resistance is 0.5  and shunt resistance is 250 . Determine the output in kW and efficiency of the motor when running on full load and taking a current of 50 A.

2.

b) A 500 V shunt motor takes 4 A on no load. The armature resistance including that of brushes is 0.2  and the field current is 1 A. Determine the output and the efficiency when the input current is i) 20 A and ii) 100 A.

c) With a neat circuit diagram, explain the procedure of conducting brake test on dc motor. 3.

4.

a) What are the advantages and disadvantages of brake test?

CO2

L1

04M

b) Obtain the equation for efficiency of the machines both as generator and motor in field test.

CO2

L2

05M

c) With neat circuit diagram, explain the procedure for conducting field test on dc series motor.

CO2

L2

06M

a) The Hopkinson’s test on two shunt machines has following results on full load: Load voltage is 250 V, Current drawn from supply excluding field current is 50 A, Motor Armature current is 380 A, generator field current is 5 A, motor field current is 4.2 A. Find the stray losses of each machine, given Ra to be 0.02 .

CO2

L1

04M

b) With a neat circuit, explain the procedure of conducting Hopkinson’s test on two identical shunt machines.

CO2

L2

05M

c) Derive the efficiency equation of the dc machines both as generator and motor in regenerative test.

CO2

L2

06M

Name & Signature of Course Instructor

[Manasa G P]