Download GTU B.Tech 2020 Winter 6th Sem 2160912 Design Of Dc Machines And Transformer Question Paper

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Subject Code:2160912

Enrolment No.

GUJARAT TECHNOLOGICAL UNIVERSITY

BE- SEMESTER-VI (NEW) EXAMINATION - WINTER 2020

Subject Name:Design of DC Machines and Transformer

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Time:02:00 PM TO 04:00 PM

Instructions:

Attempt any THREE questions from Q.1 to Q.6

Q.7 is compulsory.

Make suitable assumptions wherever necessary.

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Figures to the right indicate full marks.

1. 1. Define specific magnetic and Electrical loading.
   2. Explain the Factors affecting size of machines

   MARKS

   03

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   04

2. 1. Determine the main dimensions of the 3 limb core (i.e., 3 phase, 3 leg core 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 d?, window space factor = 0.27, window proportion = 3: 1, current density = 250 A/cm?, ON cooled (means oil immersed, self-cooled or natural cooled) transformer having + 2.5% and + 5% tapping on high voltage winding.

   07

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3. 1. What are the advantages and disadvantages-of stepped cores?
   2. Describe about the effect of frequency-on Iron losses.

   03

   04

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4. 1. Estimate the no-load current of a three phase transformer
   2. Explain Why circular coils are preferred in transformers?
   3. List out different types of windings used in power and distribution transformer.

   07

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5. 1. Discuss about cooling/of transformer using cooling tubes
   2. Only List the design aspects of dry type transformer

   03

   04

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6. 1. Show that losses in transformer are proportional to the cube of its linear dimensions
   2. Drive the expression for leakage reactance of transformer with primary and secondary cylindrical coil of equal length .state clearly the assumption made.

   07

1. 1. In which way the air gap length influence the design of machines?

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   2. List the factors that influence the separation of D and L of a dc machine.
   3. What is square pole criterion?

   03

   04

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1. 1. Discuss the choice of number of poles used in a D.C machine
   2. Write a short not on slot insulation of D C machine.
   3. Enumerate the procedure for shunt field design
   4. Discuss in detail about the design of commutator and brushes in D C machine.

   07

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Q.7 (a) Prove that in designing the D.C machine the torque is proportion to the volume of active materials. 05

OR

Q.7 (a) What do you understand by armature reaction in D C machine .Explain any one methods to reduce this? 05

Date:20/01/2021

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Total Marks: 47