8/18/2019 An assignment on Electromechanics

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EE201: Assignment 2

Due Date:  13 April, 2016, during our class   Total Marks:   20

General Instructions

•   Please write the answers in your own words. Cite the references that you may use to find the answers (includingweb-pages, if any), but  do not copy sentences and diagrams from the references .

•  Please write your name and roll number at the beginning of the assignment.

•  Main focus of this assignment is on self-study and your own thinking/analysis. Please make sure that your submissionreflects honest efforts made by you.

•   Submitted assignments shall be strictly checked against copying/plagiarism. Defaulters shall receiveno marks.

Question 1 : Exact and Approximate equivalent circuits of a transformer are given below.

V  p

I p

V  s′

I s′

I mI c

Rp   Rs′

Rc   X m

X lp   X ls′

++

−−

Fig. 1: Exact Equivalent Circuit

V  p

I p

V  s′

I s′

I mI c

Rp + Rs′

Rc   X m

X lp + X ls′

+   +

−−

Fig. 2: Approximate Equivalent Circuit

The transformer is rated at 1.2 KVA, 230/150 V. HV side is treated as primary side for this question. The parameter valuesare given below:

•   Rp  =  R′

s = 5Ω

•   X lp =  X ls′  = 6Ω•   Rc  = 1000Ω

•   X m = 1500Ω

The approximate equivalent circuit is obtained by shifting the magnetizing branch before the primary winding seriesimpedance. Answer the following with respect to these circuits.

(3 + 4 marks)

1. If the short-circuit test is carried out on the transformer, what will be the readings of all measuring instruments, if the exact transformer circuit is taken as the reference?

2. Now, based on these readings, transformer parameters are calculated taking the approximate equivalent circuit as thereference. Calculate the error in the values of all parameters as a percentage of their actual values.

8/18/2019 An assignment on Electromechanics

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Question 2   (self-study): Explain in short the working of an autotransformer. State one advantage and one limitation.(3 marks)

Question 3   (self-study): With respect to a practical transformer, briefly explain the finction of the following:

1. Transformer Oil

2. Conservator Tank

3. On-load Tap Changer

4. Breather

5. Radiator

(2 marks each)