Download Polytechnic Electrical Machine Previous Year Sample Paper 2020. Polytechnic Old Exam Paper of Electrical Machine Electrical Branch Old Exam Paper 2020. Hello Dear Readers, If you Polytechnic Students and looking for Electrical Engineering Brach 4th Semester Electrical Machine Old Exam Paper then you are in right place. Computer Tutorials Live brings Electrical Machine Previous Year Exam Paper for you.
Polytechnic Electric Machine Previous Year Sample Paper 2020
4th Semester / Electrical Engg.
Subject: ELECTRICAL MACHINE
Time: 3 Hrs. M.M. 100
Instruction: Solve All Questions
SECTION-A
Note: Attempt any ten parts. 10x2= 20
Q.1 Attempt all these questions:
i) Transformer oil is used as……………………….
ii) What are the factors on which magnitude of torque depends in D.C. motor?
iii) Define faraday’s first law of Electromagnetic induction.
iv) When Conductor cutes the ………………… an …………………. Is induced in it.
v) Name the D.C. motor which is having high starting torque.
vi) When the machine operates as a motor E is ……………………… than V.
vii) What will be parallel paths for a 4 pole Lap would D.C. Machine?
viii) In a D.C. motor starts is used to ………………… starting current.
ix) Why the core of the transformer is laminated?
x) To determine iron losses in a transformer……………… test is performed.
xi) Transformers are rated in ………………………….
xii) Define the working principle of the transformer.
Section- B
Note: Attempt any five Question. 5x6 = 30
Q.2 What is the difference between the Power Transformer and Distribution transformer?
Q.3 Explain why D.C. Series motor is having excessively high starting current.
Q.4 The no-load current of the transformer is 4 amps. At 0.2 power factor when supplies at 200 volts, 50 Calculate magnetizing current and core loss current.
Q.5 State various losses in a transformer in a transformer and condition for maximum efficiency.
Q.6 Explain the various methods of cooling of transformers.
Q.7 Describe an expression for torque developed in D.C. motor.
Section- C
Note: Attempt all the questions. 5x10 = 50
Q.8 Draw and Explain the power flow diagram of a D.C. machine working as a motor.
Q.9 Draw the phasor diagram of a transformer on load labeling all the quantities and indicating voltage drops at a leading power factor.
OR
Derive an expression for the relative of the winding material in an auto-transformer and two winding transformers.
Q.10 A 50 KVA 250/500V. The Single-phase transformer gave the following test result.
- O.C. test – 250V, 1 amp, 80 watts.
- S.C. test – 20V, 10 amp, 100 watts.
Determine the efficiency of a transformer at full load at 0.8 power factors and maximum efficiency.
Q.11 Draw and explain:
i) Speed VsIa characteristic of D.C. shunts motor.
ii) Torque VsIa characteristics
Q.12 Write down the speed equation of D.C. motor and Describe the methods to control the speed of D.C. motor.
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