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1) prepare down the energy balance equation of a motor.

2) What is the energy conversion medium in the singly-excited magnetic field system?

3) A100 kVA, 6.6kV/415V, single phase transformer has the effective impedance of (3+8j) _ referred to HV side. Evaluate full load voltage regulation at 0.8 pf lagging and 0.8 leading pf.

4)(a) Describe the working of auto transformer and prove that when transformation ratio approaches unity, amount copper used approaches smaller value.

(b) Emf per turn of single phase, 6.6kV/440V, 50 Hz transformer is approximately 12V. Compute the number of turns in HV and LV windings and net cross sectional area of the core for a maximum flux density of 1.5T.

5)(a) Get the equivalent circuit of a 200/400V, 50Hz,single phase transformer from test data given below:

OC test: 200V,0.7A,70W on LV side
SC test: 15V,10A,85W on HV side

(b) With the help of suitable circuit diagrams, describe any two kinds of three phase transformer connections

6) Determine the all day efficiency of a 500kVA, distribution transformer whose iron loss and full load copper loss are 1.5kW and 6kW respectively. In a day it is loaded as follows:

Duration (Hi)   Output(Po) in kW  Power factor(cosØ2)

     6                      400                               0.8
    10                     300                             0.75
     4                      100                               0.8
     4                         0                                 -

7) Design the circuit diagrams for conducting OC and SC tests on single phase transformer. Also describe how efficiency an d voltage regulation can be estimated by these tests.

8) What do you mean by the sumpner’s test? Design the circuit diagram to conduct this test and describe its principle.

9)(a) Deduce the condition for maximum efficiency in the transformer.

(b) A11000/230 V, 150 KVA, 1-phase, 50 Hz transformer has core loss of 1.4Kw and F.L cu loss of 1.6 Kw. Find out:

(i) kVA load for maximum efficiency and value of maximum efficiency at unity p.f

(ii) Efficiency at half F.L 0.8 pf leading

10) Describe in detail about parallel operation of single phase transformers.

Electrical & Electronics, Engineering

  • Category:- Electrical & Electronics
  • Reference No.:- M911367

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