Exam Details
| Subject | dc machines and transformers (ee) | |
| Paper | ||
| Exam / Course | b.tech | |
| Department | ||
| Organization | Government Degree College, Kamalpur | |
| Position | ||
| Exam Date | December, 2017 | |
| City, State | tripura, dhalai |
Question Paper
D D7145
Page 1 of 2
Total Pages:2
Reg
APJ ABDUL KALAM TECHNOLOGICAL UNIVERSITY
THIRD SEMESTER B.TECH DEGREE EXAMINATION, DECEMBER 2017
Course Code: EE205
Course Name: DC MACHINES AND TRANSFORMERS
Max. Marks: 100 Duration: 3 Hours
PART A
Answer all questions, each carries 5 marks. Marks
1 What is the function of equalizer ring in a lap wound dc machine?
2 Derive the emf equation of a dc generator.
3 What is starter? What is the necessity of starter in dc motor?
4 Distinguish between core and shell type transformer?
5 What is an auto transformer? Derive an expression for the saving of copper in
an autotransformer as compared to an equivalent two winding transformer?
6 Derive the condition for maximum efficiency of transformer.
7 What are the necessary conditions for parallel operation of three phase
transformer?
8 What is the purpose of tertiary winding on transformer?
PART B
Answer any two full questions, each carries 10 marks.
9 With neat diagram explain the construction of dc generator.
10 A 250V short shunt compound generator is delivering 80A. Armature, series
and shunt field resistances are 0.05Ω, 0.03Ω and 100Ω respectively. Calculate
the induced emf.
Define commutation. Explain the process of commutation with neat sketches.
11 What are the effects of armature reaction on the operation of dc machine? What
are the remedial measures taken to counter effects of armature reaction?
PART C
Answer any two full questions, each carries 10 marks.
12 Explain with neat sketch how speed control of a dc motor is done.
Draw the phasor diagram of a single phase transformer supplying to inductive
load.
13 A 6 pole 250V series motor is wave connected. There are 240 slots and each
slot has 4 conductors. The flux per pole is 0.175mWb when the motor is taking
80A. The field resistance is 0.05Ω, the armature resistance is 0.1Ω and the iron
and frictional loss is 0.1kW. Calculate speed BHP shaft torque
the pull in newtons at the rim of the pulley of diameter 25cm.
14 What are the different cooling methods used in transformer?
PART D
Answer any two full questions, each carries 10 marks.
15 The following test results were obtained on a 20kVA, 2200/220V, 50Hz single
phase transformer
OC Test(LV side) 220V 1.1A 125W
SC Test(HV side) 52.7V 8.4A 287W
D D7145
Page 2 of 2
The transformer is loaded at unity power factor on secondary side with a
voltage of 220V. Determine the maximum efficiency and load at which it
occurs.
Explain the working of Off-Load tap changing transformer with help of neat
diagram.
16 In detail explain scott connection in three phase transformer.
17 A 220kVA single phase transformer is in circuit continuously. For 8 hours in a
day, the load is 60kW at 0.8 pf. For 6 hours, the load is 80kW at unity pf and
for the remaining period of 24 hours it runs on no load. Full load copper losses
are 3.02kW and the iron losses are 1.6kW. Find all day efficiency.
What are the advantages and disadvantages of delta-delta connection?
Page 1 of 2
Total Pages:2
Reg
APJ ABDUL KALAM TECHNOLOGICAL UNIVERSITY
THIRD SEMESTER B.TECH DEGREE EXAMINATION, DECEMBER 2017
Course Code: EE205
Course Name: DC MACHINES AND TRANSFORMERS
Max. Marks: 100 Duration: 3 Hours
PART A
Answer all questions, each carries 5 marks. Marks
1 What is the function of equalizer ring in a lap wound dc machine?
2 Derive the emf equation of a dc generator.
3 What is starter? What is the necessity of starter in dc motor?
4 Distinguish between core and shell type transformer?
5 What is an auto transformer? Derive an expression for the saving of copper in
an autotransformer as compared to an equivalent two winding transformer?
6 Derive the condition for maximum efficiency of transformer.
7 What are the necessary conditions for parallel operation of three phase
transformer?
8 What is the purpose of tertiary winding on transformer?
PART B
Answer any two full questions, each carries 10 marks.
9 With neat diagram explain the construction of dc generator.
10 A 250V short shunt compound generator is delivering 80A. Armature, series
and shunt field resistances are 0.05Ω, 0.03Ω and 100Ω respectively. Calculate
the induced emf.
Define commutation. Explain the process of commutation with neat sketches.
11 What are the effects of armature reaction on the operation of dc machine? What
are the remedial measures taken to counter effects of armature reaction?
PART C
Answer any two full questions, each carries 10 marks.
12 Explain with neat sketch how speed control of a dc motor is done.
Draw the phasor diagram of a single phase transformer supplying to inductive
load.
13 A 6 pole 250V series motor is wave connected. There are 240 slots and each
slot has 4 conductors. The flux per pole is 0.175mWb when the motor is taking
80A. The field resistance is 0.05Ω, the armature resistance is 0.1Ω and the iron
and frictional loss is 0.1kW. Calculate speed BHP shaft torque
the pull in newtons at the rim of the pulley of diameter 25cm.
14 What are the different cooling methods used in transformer?
PART D
Answer any two full questions, each carries 10 marks.
15 The following test results were obtained on a 20kVA, 2200/220V, 50Hz single
phase transformer
OC Test(LV side) 220V 1.1A 125W
SC Test(HV side) 52.7V 8.4A 287W
D D7145
Page 2 of 2
The transformer is loaded at unity power factor on secondary side with a
voltage of 220V. Determine the maximum efficiency and load at which it
occurs.
Explain the working of Off-Load tap changing transformer with help of neat
diagram.
16 In detail explain scott connection in three phase transformer.
17 A 220kVA single phase transformer is in circuit continuously. For 8 hours in a
day, the load is 60kW at 0.8 pf. For 6 hours, the load is 80kW at unity pf and
for the remaining period of 24 hours it runs on no load. Full load copper losses
are 3.02kW and the iron losses are 1.6kW. Find all day efficiency.
What are the advantages and disadvantages of delta-delta connection?
Other Question Papers
Subjects
- analog electronic circuits (ee)
- basics of electrical engineering
- basics of mechanical engineering
- circuits and networks (ee)
- computer aided design and analysis (ma, me, mp, pe)
- computer programming (ee)
- dc machines and transformers (ee)
- digital electronics and logic design (ee)
- dynamics of machinery (me, mp, au, pe)
- fluid mechanics and machinery
- heat and mass transfer (ma, me, au)
- machine design (pe)
- machine tools and digital manufacturing (ie, me)
- manufacturing technology
- manufacturing technology (ie, me, ma)
- material science (ee)
- measurements and instrumentation (ee)
- mechanics of machinery (me, mp, pe)
- mechanics of solids (me,mp,ma,mt,au,pe,sf)
- mechanics of solids(au, ma, me, mp, mt, pe, sf)
- metallurgy and materials engineering(mc, mp, ma, me, pe)
- metrology and instrumentation (me, mp, pe)
- synchronous and induction machines (ee)