Aim :1. Construct a full wave rectifier.

Requirement

SR.NO.	Tools/Instrument	Size	Qty	SR.NO.	Materials/Machinery	Size	Qty
1	Long nose plier	200mm	01	1.	Silicon diode	IN4007	02
2	Connector screw driver	75mm	1	2	Step down taransformer	220/12-0-12 v	1
3	Side cutting plier	150mm	01	3	Base board C.B	2*2	01
4	Electrician knife	75mm	01	4	Flexible wire Red and Black colour	7/0.36	as requird

PROCEDURE :-
1).Draw the circuit diagram.
2).Test the continuity of the primary and secondary winding of the given transformer.
3).Referring to fig  follow  order of steps given below.
-- Mount the test transformer on base board using  suitable size nut,washer and bolt.
-- Mount the rectifier diodes on lug board soldering.
-- Solder the wire connection and the three core power cord.
4).Connect A.C main to the transformer ON main measure and record the main voltage and transformer secondary voltage Vs(rms).
5).measure the rectifier D.C voltage Vde across resistor RL using multimeter/ voltmeter.

PRECAUTIONS .
1).Connect diodes proper directions.
2).Do not lose contact on the base board of silicon diode


Aim:2. To measure the internal resistance of a battery.

Requirement

SR.NO	Tools/Instrument	Size	Qty	SR.NO.	Materials/Machinery	Size	Qty
1	Insulated combination plier	200mm	01	1.	Rheostate wire wound	1k ohm/50A	01
2	Connector screw driver	75mm	1	2	Knife switch	220v 50A	01
3	Electrician knife	75mm	01	3	Battery	12v	01
4	Volt meter M.C	0025v	01	4	Wire pieces	7/0.36	as requird
5	Ammeter M.C	0-50A	01

PROCEDURE :-
1).Select the meter accessories,etc and connect as per diagram.
2).check connection for second time.
3). Not down the open circuit voltage of the battery.
4). close the switch ,s, and adjust the resistance to get the minimum readable current.
5). Not down the readings on voltmeter and ammeter.
6).Increase the  current and repeat readings.
7). Note down the reading in table and calculate the result.

PRECAUTIONS.
1). Do not cut of the resistance completely when the switch is closed.
2). Do not increase the current more than rated current of the resistance.
3).Do not keep the circuit ON  for long time.


Aim 3:- To control the speed of ceiling fan motor by the fan regulator.

Requirement

SR.NO.	Tools/Instrument	Size	Qty	SR.NO.	Materials/Machinery	Size	Qty
1	Combination plier	200mm	01	1.	Lead wire	1.55 sqm	as requird
2	Electrician screw driver	75mm	1	2	Switch (S.P)	250 / 0A	01
3	Side cutting plier	150mm	01
4	Electrician knife	75mm	01
5	Screw driver	150mm	01
6	Ceiling fan		01
7	Fan regulator		01

PROCEDURE:-
1). Draw the connection diagram.
2).Not the name plate detail of the given ceiling fan motor.
3).Identify the terminal of the ceiling fan motor.
4). select the suitable range of  regulator.
5).Connect the fan regulator in series with the fan regulator.
6).Switch ON the main supply.
7).Control the speed of the fan regulator by the rotary switch knob rotate of the regulator.

PRECAUTIONS.
1).Do not connect the regulator in parallel with the supply.
2).Increase the speed of the fan motor cut of the internal resistance step by step rotate the rotary switch
     of the regulator.


Aim:4:- Measure of the resistance by using post office box.

Requirement

SR.NO.	Tools/Instrument	Size	Qty	SR.NO.	Materials/Machinery	Size	Qty
1	Nose plier	150mm	01	1.	Deferent type of restance		one each
2	Connector screw driver	75mm	1
3	Electrician knife	75mm	01
4	Post office box		01
5	Galvanometer			2	P.V.C wire	1.55sq	3m
6	Battery	06v	01	3	Battery lead		as requird
7	Insulated combination plier	200mm	01

PURPOSE:- Post office box connections selecting ratios- calculation of resistance.

PROCEDURE > 

1).Connect the battery galvanometer and unknown resistance at the marked terminals as per diagram.

2).Adjust two 10 ohm and 1 ohm i each of the ratio arms P and Q.

3).Adjust 1 ohm in variable (arm)R.

4).press the push button and sec  the deflection of the galvanometer.

NOTE} press battery switch first and then the galvanometer switch.

5).Adjust the max resistance in R and repeat the operation.

NOTE} the deflection of the meter must be on the other side other wise very the resistance in ratio arm 

            P and Q.

6). very the resistance R  until the galvanometer null point.

Part - A(Objective test items)- july 2007

Q:1. The relationship between power, voltage and current can be represented by a divided triangle.

        Draw a power triangle for DC circuit.

Ans:1. p/v/i

Q:2. Identify the fault in the battery charging circuit shown.

Ans:2. Polarity of battery is wrongly connected to the rectifier supply.

Q:3. What will happen if a permanent magnet moving coil instrument is connected to AC supply?

Ans:3. NO deflection or NO readings.

Q:4. In a serial lamp set the number of lamps used are generally 5% more than the calculated number 

        of lamps fora given voltage.

Ans:4. To compensate for higher voltage fluctuations.

Q:5. What are the possible causes of a food mixer running hot at normal speed?

        Two causes are

       a) sparking at commutator

       b) Over voltage.

       What are other two causes.

Ans:5. a) Overloading.

           b) Partial short in the field or armature.

Q:6. Earth tester is mainly used for measuring earth electrode resistance.

        Given two more uses of the earth tester.

Ans:6. a) Earth continuity test.

          b) Soil Resistivity.

Q:7. What is mutual induction?

Ans:7. Changing magnetic flux of one coil induces emf in an other electrically isolated coil.

Q: 8. You find a coil with core in contactors.

         What is the main function?

Ans:8. Switch ON / OFF the supply.

Q:9. What is the material used for the core of a high frequency transformer?

Ans:9. Ferrite core.

Q:10.  More retentivity magnetic material is to be used for transformers core.

          Name the material is used for the core in power transformers?

Ans:10. Silicon steel.

Q:11. A mechanism is incorporated in circuit breakers to switch off the circuit breaker at fault cindition 

         either automatically or manually at the desired time.

         What is the mechanism known as?

Ans:11. Trip mechanism.

Q:12. The input voltage of a regulator circuit is different from the output voltage.

           What can you state about the value of the input voltage compared to the output voltage?

Ans:12. Higher or lower than output voltage and is not constant.

Q:13. a) How many contactors are there in fully automatic star-delta starters?

          b) Name the contactors in fully automatic star-delta starters?

Ans:13. a) Automatic star-delta starters have three contuctors.

             b) One main conductor with OL relay, one star contactor and one delta contactor.

Q:14. inspite of no electrical fault in the fan motor and its wiring circuit, it is still running slow, even by

          applying rated voltage. The blades are not deformed and ther is no wobbling.

          What are the reasons?

Ans:14. i) No lubrication / Dry lubrication / Resistive bearing.

             ii) Bearing fault.

Q:15. Domestic mixers / liquidizer generally use universal motor, and it has two windings.

          a) What are these windings?

          b) How they are connected together?

Ans:15.a) Armature winding and field winding.

            b) The two windings are connected in series.

Q:16. In figure part of a fluorescent lamp circuit is shown.

        a) What is the name of this part?

        b) How it is connected initially at the time of starting?

Ans:16. a) Starter            b) In series with the filament.

Q:17. You have to replace a thermostat in a geyser.

          How do you connect the thermostat with the heating element?

Ans:17. In series with the heating elements.

Q:18. What is the function of a fuse with respect to vaule of current in a circuit?

Ans:18. The fuse must open the circuit, if the current is greater than the reted value of the circuit current.

Q:19. The charging  curve of a RC circuit is shown in the figure.

          The value og vc is 90 v.

           Calculate

          a) the value v c11 fot 1t,

          b) the value vc2 for 2t,

Ans:19. a) vc1=90x63/100= 56.7v          b) vc2=90x86/100=77.4v

Q:20. Among various type of bulbs one type of bulb should not be handled by bare hands even 

          while replacing the bulb.  

          What is the type of lamp?

Ans:20. Hologen lamps.

Part - B - july 2007

Q:1. a) Describe the purpose of earting?

        b) A battery operated circuit requires 6v and a capacity of 4 Ah. Cells rated at 1.5v and 2 Ah 

            are available to do the job.

         Calculate the required arrangement of cells.

        c) State the different types of singale phase watt meter.

Ans:1. a) The purpose of earthing is to provide protection to personnel, equipment and circuits by 

               eliminating the possibility of dangerous or excessive voltage.

           b) No of cells in series= vr/vp.c=6v/1.5v=4cells

               No of parallel row= Ahr/Ahp.c=4Ah//2Ah=2 rows

            c) There are three types of wattmeters,they are

                 (i) Dynamometer type

                 (ii) Induction type

                 (iii) Electrostatic type.

Q:2. a)Explain the purpose of the fuse in a circuit?
        b) A four pole generator having a simplex wave wound armature has 51 slots,each slot contanining
           20 conductors.
           What will be the voltage generated in the machine, when driven at 1500 rpm.assuming the flux
            per pole is 7.0 mWb?

Ans:2. a) A fuse is a safety device used for the purpose of protecting a circuit against excess current. In 
               the event of excessive current, the fuse element melts and opens up the circuit there by protecting
               equipment machine from damage.

            b) Data given
                Z=51x20=1020
                P=4
                N=1500 RPM
                Q=7x10-3wb
                 A=2 (wave winding)
                We know E=thita ZN/60xP/A=7x10-3squrex1020x1500/60x4/2=357v

Q:3. a) List the conditions to be fulfilled to connect two transformer in parallel.
        b)When the load is removed from an AC generator, its terminal voltage rises from 480v at ful load
           to 660v at no load.
            Calculate the voltage regulation.
         c) What is the function of centrifugal switch in single phase AC motor?

Ans:3. a) To operate two or more transformer in parallel, the following conditions to be fuldilled. They are
           
               (i) Voltage ratings of transformer must be same.
               (ii) Impedance rating of transformer must be same.
               (iii) Polarity of the transformer must be same.
               (iv) Phase sequence of the transformer must be same.
         
             b) Data given
                 No load voltage=660v
                 Full load voltage=480v

                  % Regulation = Vnl - Vfl/Vflx100
                   = 660-480/480x100=37.5%

             c) The centrifugal switch is located inside the motor and is connected in series with the starting 
                 winding. The function of the centrifugal switch is to disconnect starting winding after the rotor 
                  has reached 75 to 80% of the rated speed.

Q:4. a) State the necessity of a star-delta starter for a 3-phase squirrel cage induction motor.
        b) State the definition of a circuit breaker and list the various types of circuit breakers.
        c) A 400v, 3-phase, 8 pole, 50 Hz squirral cage motor has a rated full load speed of 720 rpm.
            Determine the synchronous Speed.

Ans:4 a) Squirral cage motor during starting time it will take 5-6 times of full load current for a few seconds.
             This starting current will cause too much fluctuations in the power lines and disturb the other loads.
             On the other hand, if all the squirral cage motors connected to the power lines are started at the 
              same times, they may momentarily over load the power lines.
             Because of these reasons, the applied voltage to the squirral cage motors needs to be reduced
             during the starting periods and regular supply could be given when the motor picks up its speed. 
             For This purpose only star-delta starters are required to start the squirral cage motors.

          b) Definition:
              A circuit breaker is a device capable of making and breaking a circuit under normal conditions 
              as well as under abnormal conditions such as those of short circuit.
              Types:
           (i) Air break circuit breaker.(ACB).
           (ii) Oil circuit breaker.(OCB)
           (iii) Air blast circuit breaker.(ABCB)
           (iv) Miniature circuit breaker.(MCB)
           (v) Earth leakage circuit breaker.(ELCB)

          c) Solution:
               Synchronous speed Ns=120xf/p=120x50/8=750 rpm