5104

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					     BOARD OF TECHNICAL EDUCATION
                          PORVORIM-GOA
                    November,2010 Examinations

Programme: Electrical Engineering

Subject: Testing & Maintenance of Electrical Equipments(5104)

Time Duration: 3 Hrs.                                Max. Marks: 75
Instructions: 1) All Questions are compulsory.
              2) Figures to the right indicate full marks.
              3) Assume suitable additional data if required.

Q.No.1. Answer any five of the following:                                     5 x 3 = 15
     a) State two points of distinction between acceptance test & pre-
         commissioning test.
     b) Generally large capacity machines are tested by using indirect
         testing method say True or False & justify your choice.
     c) Define i) Mechanical efficiency        ii) Electrical efficiency iii)
         Overall efficiency in a d.c. machine.
     d) What is the significance of polarity test to be performed on
         transformer? How is it performed?
     e) What is the significance of H.V. test on induction motor? When
         & where is it performed?
      f) Why is the sudden three phase short circuit test performed on
         a synchronous machine?
     g) Differentiate between Preventive maintenance & breakdown
         maintenance of electrical equipment.
     h) Enlist the various “type tests” performed on Induction motor.

Q.No.2. Answer any two of the following:                                  2 x 6 = 12
     a) With the help of neat circuit diagram, state the various steps
        required to perform Swinburn’s test on D.C. machine.
     b) With the help of neat circuit diagram, explain the regenerative
        test to be performed on d.c. machine in order to determine its
        efficiency.
     c) Two similar d.c. machines each rated at 500 V, 1000 KW were
        tested by Hopkinson’s test. The test data obtained is as follows:
        Output current of generator = 2000 A
        Input current from supply mains = 380 A
        Shunt field current of generator = 22 A
        Shunt field current of motor = 17 A
        Resistance of armature of each machine is 0.01 ohm. Calculate
        efficiency of generator at full load by assuming equal iron,
        friction & windage losses.

Q.No.3. Answer any two of the following:                              2 x 6 = 12
     a) With the help of neat circuit diagram, explain in brief the
        method of determining efficiency of transformer by performing
        ‘Sumpner test’.
     b) How insulation resistance is measured for Power transformer?
        What are the minimum permissible values of insulation
        resistance of transformer windings?
     c) Obtain an equivalent circuit of 200/400 V, 50 Hz, 1 phase
        transformer from the following test data:
        O.C. Test: 200 V, 0.7 A, 70 W on L.V. side.
        S.C. Test : 15 V, 10 A, 85 W, on H.V. side.
        Calculate the secondary voltage when delivering 5 KW at 0.8
        p.f. lagging, the primary voltage being 200V.
                                                                        ………2/-
                                          -2-

Q.No.4. Answer any two of the following:                                  2 x 6 = 12
     a) Explain with the help of neat circuit diagram, how no load test
        and blocked rotor test is performed on three phase Induction
        motor. Also specify the data required to be obtained to perform
        such test.
     b) For the heat run test to be performed on an Induction motor,
        explain the procedure to perform it. Also explain any one
        method used to measure temperature of winding.
     c) The power input to a 500 V, 50 Hz, 6 pole, 3 phase Induction
        motor running at 975 R.P.M. is 40 Kw. The stator loss is 1Kw
        calculate i) The slip ii) rotor copper loss iii) Efficiency.

Q.No.5. Answer any two of the following:                               2 x 6 = 12
     a) State the different types of losses we came across in a
        synchronous machine. Explain the method of determining any
        one of such losses of your choice.
     b) Enlist various methods of measurement of d.c. resistance of
        field and armature winding of synchronous machine. Explain
        any one of such method in brief. What is the possible cause of
        higher value of resistance in comparison to their permissible
        variation from designed value?
     c) Explain the method of testing of field system of electrical
        machine for its correct polarity of magnetic pole & short
        circuited winding turns.
     d) State the various commissioning tests to be performed on 3
        phase Induction motor.

Q.No.6.   Write short note on any three:                                  3 x 4 = 12
     a)   List of checks on Induction motor if it fails to short
     b)   Preventive maintenance measures in transformer
     c)   Impregnation of varnishes in electrical machines
     d)   Procedure of inspection of electrical machines prior to its
          installation

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Description: question papers of previous exams of board of technical education