Download GTU (Gujarat Technological University Ahmedabad) B.Tech/BE (Bachelor of Technology/ Bachelor of Engineering) 2020 Winter 6th Sem 2160912 Design Of Dc Machines And Transformer Previous Question Paper
Enrolment No.___________
GUJARAT TECHNOLOGICAL UNIVERSITY
BE- SEMESTER?VI (NEW) EXAMINATION ? WINTER 2020
Subject Code:2160912 Date:20/01/2021
Subject Name:Design of DC Machines and Transformer
Time:02:00 PM TO 04:00 PM Total Marks: 47
Instructions:
1. Attempt any THREE questions from Q.1 to Q.6
2. Q.7 is compulsory.
3. Make suitable assumptions wherever necessary.
4. Figures to the right indicate full marks.
MARKS
Q.1 (a) Define specific magnetic and Electrical loading.
03
(b) Explain the Factors affecting size of machines
04
(c) Determine the main dimensions of the 3 limb core (i.e., 3 phase, 3 leg core
07
type transformer), the number of turns and cross-sectional area of the
conductors of a 350 kVA, 11000/ 3300 V, star / delta, 3 phase, 50 Hz
transformer. Assume: Volt / turn = 11, maximum flux density = 1.25 T. Net
cross-section of core = 0.6 d2, window space factor = 0.27, window
proportion = 3: 1, current density = 250 A/cm2, ON cooled (means oil
immersed, self-cooled or natural cooled) transformer having ? 2.5% and ?
5% tapping on high voltage winding.
Q.2 (a) What are the advantages and disadvantages of stepped cores?
03
(b) Describe about the effect of frequency on Iron losses.
04
(c) Estimate the no-load current of a three phase transformer
07
Q.3 (a) Explain Why circular coils are preferred in transformers?
03
(b) List out different types of windings used in power and distribution
04
transformer.
(c) Discuss about cooling of transformer using cooling tubes
07
Q.4 (a) Only List the design aspects of dry type transformer
03
(b) Show that losses in transformer are proportional to the cube of its linear
04
dimensions
(c) Drive the expression for leakage reactance of transformer with primary and
07
secondary cylindrical coil of equal length .state clearly the assumption made.
Q.5 (a) In which way the air gap length influence the design of machines?
03
(b) List the factors that influence the separation of D and L of a dc machine.
04
What is square pole criterion?
(c) Discuss the choice of number of poles used in a D.C machine
07
Q.6 (a) Write a short not on slot insulation of D C machine.
03
(b) Enumerate the procedure for shunt field design
04
(c) Discuss in detail about the design of commutator and brushes in D C
07
machine.
1
Q.7 (a) Prove that in designing the D.C machine the torque is proportion to the
05
volume of active materials.
OR
Q.7 (a) What do you understand by armature reaction in D C machine .Explain any
05
one methods to reduce this?
*************
2
This post was last modified on 04 March 2021