LIST OF QUESTIONS

ELECTRICAL ENGINEERING PRACTICAL VIVA-VOCE QUESTIONS LIST OF QUESTIONS: COMMON QUESTIONS: 1) WHY DO WE REPLACE CURRENT SOURCE WITH A OPEN CIRCUIT FOR CALCULATING RTH? 2) WHY DO WE REPLACE VOLTAGE SOURCE BWITH A SHORT CIRCUIT FOR CALCULATING RTH? 3) WHAT DO YOU MEAN BY LOAD? 4) WHICH QUANTITY IS SAME IN SERIES CIRCUIT? 5) WHICH QUANTITY IS SAME IN PARALLEL CIRCUIT? 6) WHAT DO YOU MEAN BY RESISTANCE OF A CONDUCTOR? 7) WHAT DO YOU MEAN BY IDEAL VOLTAGE SOURCE? 8) WHAT DO YOU MEAN BY IDEAL CURRENT SOURCE? 9) WHAT DO YOU MEAN BY PRACTICAL VOLTAGE SOURCE? 10) WHAT DO YOU MEAN BY PRACTICAL CURRENT SOURCE? 11) WHAT DO YOU MEAN BY POSITIVE TEMPRATURE COEFFICIENT OF RESISTANCE? 12) WHAT DO YOU MEAN BY NEGATIVE TEMPRATURE COEFFICIENT OF RESISTANCE? 13) WHAT DO YOU MEAN BY ZERO TEMPRATURE COEFFICIENT OF RESISTANCE? 14) WHICH COLOR WIRE IS THE POSITIVE WIRE OF MULTIMETER? 15) WHICH COLOR WIRE IS THE NEGATIVE WIRE OF THE MULTIMETER? 16) WHEN THE DIGITAL MULTIMETER READ VOLTAGE WITH NEGATIVE SIGN, AT THAT TIME THE POINT AT WHICH RED PROBE YOU HAVE CONNECTED IS AT __________ POTENTIAL? 17) WHAT DOES IT MEAN WHEN THE METER READ VOLTAGE OR CURRENT WITH NEGATIVE SIGN? 18) THE RESISTANCE OF A CONDUCTOR___________ IF WE INCREASE THE CROSS-SECTIONAL AREA OF A CONDUCTOR? 19) THE RESISTANCE OF A CONDUCTOR___________ IF WE INCREASE THE LENGTH OF A CONDUCTOR? 20) IF THE VALUE OF VOLTAGE IOS IN VOLTS AND CURRENT IS IN MILLIAMPERES THEN VALUE OF RESISTANCE IS IN__________? 21) WHY DO WE CONNECT AMMETER IN SERIES? 22) WHY DO WE CONNECT VOLTMETER IN PARALLEL? 23) WHAT DO YOU MEAN BY RESISTANCE? 24) WHAT DO YOU MEAN BY IMPEDANCE?

KIRCHHOFF’S LAWS: 1) 2) 3) 4)

STATE KIRCHHOFF’S VOLTAGE LAW? STATE KIRCHHOFF’S CURRENT LAW? STATE OHM’S LAW? WHICH LAW IS REQUIRED FOR APPLYING KIRCHHOFF’S VOLTAGE LAW TO A CLOSED PATH IF WE KNOW ONLY RESISTANCES AND CURRENT FLOWING IN THAT PATH? 5) IS KIRCHHOFF VOLTAGE LAW APPLICABLE TO LOOP CONTAINING OPEN IN IT? 6) IS KIRCHHOFF’S LAWS APPLICABLE TO A.C CIRCUITS?

7) NAME THE MATERIAL USED OR EQUIPMENTS REQUIRED FOR PERFORMING KIRCHHOFF’S LAWS EXPERIMENT? 8) HOW CAN YOU FIND OUT VOLTAGE RISE OR VOLTAGE DROP OR POSITIVE AND NEGATIVE SIGN USING MULTIMETER? 9) HOW CAN YOU FIND OUT DIRECTION OF CURRENT USING MULTIMETER? 10) IN RESISTIVE LOAD BANK RESISTOR ARE CONNECTED IN SERIES OR PARALLEL? 11) IF VOLTAGE RISE IS TAKEN AS POSITIVE THEN VOLTAGE DROP IS TAKEN AS________? 12) IF INCOMING CURRENT IS TAKEN AS NEGATIVE THEN OUTGOING CURRENT IS TAKEN AS ____________?

THEVENIN’S THEOREM: 1) EXPLAIN IN BREIF HOW TO THEVENIZE THE GIVEN CIRCUIT? 2) IS THEVENIN’S THEOREM APPLICABLE TO A.C CIRCUITS? 3) NAME THE MATERIAL USED OR EQUIPMENTS REQUIRED FOR PERFORMING THEVENIN’S THEOREM EXPERIMENT? 4) HOW DO WE MEASURE RTH PRACTICALLY? 5) HOW DO WE MEASURE VTH PRACTICALLY? 6) HOW DO WE CALCULATE RTH THEORETICALLY? 7) HOW DO WE CALCULATE VTH THEORETICALLY? 8) WHAT DO YOU MEAN BY RTH OF A CIRCUIT? 9) STATE THEVENIN’S THEOREM?

SUPERPOSITION THEOREM: 1) HOW DO YOU PERFORM SUPERPOSITION THEOREM? 2) IS SUPERPOSITION THEOREM APPLICABLE TO A.C CIRCUITS? 3) NAME THE MATERIAL USED OR EQUIPMENTS REQUIRED FOR PERFORMING SUPERPOSITION THEOREM EXPERIMENT? 4) IN SUPERPOSITION THEOREM WHEN DEACTIVATE VOLTAGE SOURCE WHY WE REPLACE IT WITH A SHORT CIRCUIT? 5) IN SUPERPOSITION THEOREM WHEN DEACTIVATE CURRENT SOURCE WHY WE REPLACE IT WITH A OPEN CIRCUIT? 6) SUPERPOSITION THEOREM IS APPLICABLE TO CIRCUIT CONTANING ANY NUMBER OF LINEAR INDEPENDENT SOURCES? 7) STATE SUPERPOSITION THEOREM? MAXIMUM POWER TRANSFER THEOREM: 1) HOW DO YOU PERFORM MAXIMUM POWER TRANSFER THEOREM?

2) IS MAXIMUM POWER TRANSFER THEOREM APPLICABLE TO A.C CIRCUITS? 3) NAME THE MATERIAL USED OR EQUIPMENTS REQUIRED FOR PERFORMING MAXIMUM POWER TRANSFER THEOREM EXPERIMENT? 4) UNDER WHAT CONDITION MAXIMUM POWER IS DELIVERED TO THE LOAD RESISTANCE IN A CIRCUIT CONTAINING ONLY RESISTANCES? 5) NAME ANY APPLICATIONS OF MAXIMUM POWER TRANSFER THEOREM? 6) STATE MAXIMUM POWER TRANSFER THEOREM? TRANSFORMERS: 1) 2) 3) 4) 5)

WHAT ARE THE APPLICATIONS OF TRANFORMER? TRANSFORMER IS A CONSTANT POWER DEVICE, TRUE OR FALSE? WHAT DO YOU MEAN BY VOLTAGE REGULATION OF A TRANSFORMER? WHICH ARE TWO WINDINGS IN A TRANSFORMER AS FAR AS VOLTAGES ARE CONCERNED? WHAT DO YOU MEAN BY VOLTAGE TRANSFORMATION RATIO OF SINGLE PHASE TRANSFORMER? 6) WHAT DO YOU MEAN BY CURRENT RATIO OF SINGLE PHASE TRANSFORMER? 7) WHAT DO YOU MEAN BY TURNS RATIO OF SINGLE PHASE TRANSFORMER? 8) CAN TRANSFORMER WORK ON DC SUPPLY? 9) IF THERE ARE MORE NUMBER OF TURNS ON SECONDARY WINDING AS COMPARED TO PRIMARY WINDING, THEN WHICH WINDING IS HIGH VOLTAGE WINDING? 10) NAME THE APPARATUS USED FOR PERFORMING EXPERIMENT ON DETERMINATION OF VOLTAGE AND CURRENT RATIOS OF TRANSFORMER? 11) NAME THE APPARATUS USED FOR PERFORMING EXPERIMENT ON DETERMINATION OF VOLTAGE REGULATION AND EFFICIENCY OF TRANSFORMER? 12) THE VALUE OF VOLTAGE REGULATION SHOULD BE ________FOR A GOOD TRANSFORMER? 13) WHICH WINDING WIRE IS THICHER OUT OF TWO WINDINGS OF A TRANSFORMER? 14) UNDER NO LOAD CONDITION TERMINAL VOLTAGE AND VOLTAGE INDUCED VOLTAGE ON SECONDARY SIDE ARE __________? 15) WHAT ARE THE DIFFERENT TYPES OF TRANSFORMERS WITH RESPECT TO THE CORES OF TRANSFORMERS? DC MOTOR: 1) IN WHAT MANNER FIELD WINDING AND ARMATURE WINDING OF A DC SERIES MOTOR IS CONNECTED? 2) IN WHAT MANNER FIELD WINDING AND ARMATURE WINDING OF A DC SHUNT MOTOR IS CONNECTED? 3) WHY DO WE NEED STARTER FOR STARTING OF A DC MOTOR? 4) WHAT DO YOU MEAN BY BACK EMF IN A DC MOTOR? 5) WHAT IS THE FREQUENCY OF THE VOLTAGE APPLIED TO DC SHUNT MOTOR? 6) HOW THE DIRECTION OF THE DC SHUNT MOTOR CAN BE REVERSED?

7) WILL THE DIRECTION OF THE DC MOTOR GETS REVERSED IF THE SUPPLY TERMINALS ARE INTERCHANGED? 8) WHY DO WE CALLED ROTOR OF A DC MOTOR AS ARMATURE? MEASUREMENT OF POWER: 1) WHICH ARE THE TWO COILS OF WATTMETER? 2) WHAT DOES L IN A WATTMETER TERMINALS TERMINOLOGY STANDS FOR? 3) WHAT DOES M IN A WATTMETER TERMINALS TERMINOLOGY STANDS FOR? 4) WHAT DOES V IN A WATTMETER TERMINALS TERMINOLOGY STANDS FOR? 5) THE POWER FACTOR OF A PURELY RESISTIVE LOAD IS_______? 6) THE POWER FACTOR OF A PURELY CAPACITIVE LOAD IS ____? 7) THE POWER FACTOR OF A PURELY INDUCTIVE LOAD IS ______? 8) WHAT DOES WATTMETER READS, INSTANTANEOUS POWER OR AVERAGE POWER? 9) WHAT DOES AC AMMETER READS, PEAK VALUE OR RMS VALUE? 10) WHAT DOES AC VOLTMETER READS, PEAK VALUE OR RMS VALUE? 11) THE POWER INDICATED BY WATTMETER INCREASES OR DECRESASES AS WE INCREASE THE LOAD IN LOAD BANK? 12) CAN WE CALCULATE ENERGY AFTER MEASURING POWER WITH WATTMETER?

EXPERIMENT NO. AIM:

MEASUREMENT OF POWER AND POWER FACTOR IN A SINGLE PHASE AC CIRCUIT USING

DYNAMOMETER TYPE WATTMETER.

SCOPE: i)

ACTIVE POWER CAN BE MEASURED FOR ANY TYPE OF LOAD.

ii) POWER FACTOR AND REACTIVE POWER CAN BE CALCULATED IF WE ALSO MEASURE VOLTAGE ACROSS AND CURRENT FLOWING THROUGH THE LOAD.

APPRATUS: i)

CONNECTING WIRES,

ii) AMMETER (0-5A) – 1NOS. iii) VOLTMETER (0-300V) – 1NOS. iv) WATTMETER (10A, 300V) – 1 NOS. v) LOAD BANK. vi) AUTOTRANSFORMER.

CIRCUIT DIAGRAM:

THEORY: THE ACTIVE POWER OR AVERAGE POWER OR REAL POWER IN ANY SINGLE PHASE LOAD CAN BE MEASURED WITH THE HELP OF DYNAMOMETER TYPE WATTMETER. THE WATTMETER CONTAINS TWO COILS CURRENT COIL AND PRESSURE OR VOLTAGE COIL. CURRENT COIL (CC) IS CONNECTED IN SERIES WITH THE LOAD AND PRESSURE COIL (PC) IS CONNECTED IN PARALLEL WITH THE LOAD. WATTMETER HAS FOUR TERMINALS M, L, C, V. THE TERMINAL M IS CONNECTED TO MAINS SUPPLY, TERMINAL L IS CONNECTED ON THE LOAD SIDE, TERMINAL V IS CONNECTED TO THE OTHER END OF THE LOAD AND TERMINALS M AND C ARE SHORT CIRCUITED. IF WE ALSO CONNECT THE AMMETER AND VOLTMETER ALONGWITH THE WATTMETER, WE CAN ALSO MEASURE THE VOLTAGE ACROSS THE LOAD AND CURRENT THROUGH IT AND THE PRODUCT OF VOLTAGE AND CURRENT WILL GIVE APPARENT POWER (VI). AFTER KNOWING ACTIVE AND APPARENT POWER WE CAN EASILY CALCULATE POWER FACTOR OF THE LOAD.

FORMULAE: ACTIVE POWER, P = VIcosФ, APPARENT POWER, S = VI, POWER FACTOR, cosФ = (ACTIVE POWER/APPARENT POWER) = P/S.

PROCEDURE: 1) CONNECT THE CIRCUIT AS SHOWN IN THE CIRCUIT DIAGRAM USING CONNECTING WIRES AND THE MEASURING INSTRUMENTS. 2) SET THE VALUE OF VOLTAGE AT ONE LEVEL BY LOOKING AT VOLTMETER. 3) INITIALLY KEEP THE SWITCH OF LOAD BANK OPEN, AT THIS TIME CURRENT AND POWER WILL BE ZERO. TAKE THE READING OF ALL THE THREE METERS. 4) NOW CLOSE THE SWITCH OF LOAD BANK, AND INCREASE THE LOAD GRADUALLY BY CLOSING ONE SWITCH AT A TIME. 5) EVERY TIME WHEN YOU INCREASE THE LOAD, AJDUST THE VOLTAGE TO ITS INITIAL VALUE USING AUTOTRANSFORMER. 6) NOTE DOWN THE READING OF ALL THE METERS, EVERY TIME WHEN YOU INCREASE THE LOAD.

7)

CALCULATE POWER FACTOR USING ABOVE GIVEN FORMULA.

OBSERVATION TABLE: SR NO.

VOLTAGE (V)

1 2 3 4 5 6

CALCULATIONS:

RESULT AND CONCLUSION:

CURRENT (A)

ACTIVE POWER,P (W)

POWER FACTOR, cosФ

EXPERIMENT NO. AIM:

TO STUDY STARTING OF DC SHUNT MOTOR USING THREE POINT STARTER AND REVERSING OF DC

SHUNT MOTOR.

SCOPE: i)

NEED OF STARTER AT THE TIME OF STARTING.

ii) REVERSING OF DC SHUNT MOTOR.

APPRATUS: i)

CONNECTING WIRES,

ii) DC SHUNT MOTOR, iii) THREE POINT STARTER, iv) VARIABLE DC SUPPLY (30A),

CIRCUIT DIAGRAM:

THEORY: DC SHUNT MOTOR IS WIDELY USED MOTOR IN INDUSTRIAL APPLICATIONS. IT IS A CONSTANT SPEED MOTOR IDEALY BUT THERE SOME DROP IN SPEED FROM NO-LOAD TO FULL-LOAD PRACTICALLY. THE DC SHUNT MOTOR IS STARTED WITH THE HELP OF THREE POINT STARTER. STARTER CONSISTS OF RESISTANCES IN SERIES WITH ARMATURE WHICH LIMITS THE STARTING CURRENT OF MOTOR AND THE RESISTANCE IS GRADUALLY CUT-OUT AS THE MOTOR GAINS SPEED. ONCE THE MOTOR IS ATTAINING FULL SPEED ALL RESISTANCES OF STARTER HAS BEEN CUT OUT AND MOTOR RUN AT RATED SPEED. SINCE THE BACK EMF OF MOTOR IS ZERO AT THE TIME OF STARING AS MOTOR IS AT REST SO THE HEAVY CURRENT CAN FLOW THROUGH ARMATURE AND TO LIMIT THIS STARTER IS USED. THE DIRECTION OF DC SHUNT MOTOR CAN BE REVERSED OR CHANGED EITHER BY INTERCHANGING ITS FIELD TERMINALS OR ARMATURE TERMINALS BUT NOT BOTH, BECAUSE CHANGING BOTH THE FIELD AND ARMATURE TERMINALS WILL NOT CHANGE THE DIRECTION OF MOTOR AND THE MOTOR WILL CONTINUE TO RUN IN SAME DIRECTION.

PROCEDURE: 1) CONNECT THE CIRCUIT AS SHOWN IN FIGURE 1. 2) NOW SWITCH ON THE DC SUPPLY SOURCE AND MOVE THE STARTER ARM GRADUALLY. THE MOTOR WILL PICK UP THE SPEED SLOWLY AND FINALLY RUNS AT RATED SPEED. 3) NOTE THE DIRECTION OF MOTOR. 4) NOW SWITCH OFF THE SUPPLY AND INTERCHANGE THE FIELD WINDING TERMINALS AS SHOWN IN FIGURE 2, NEGATIVE OF SUPPLY CONNECTED TO F OF FIELD AND POSITIVE NOW CONNECTED TO FF OF FIELD. 5) AGAIN MOVE THE STARTER ARM GRADUALLY. THE MOTOR WILL PICK UP THE SPEED SLOWLY AND FINALLY RUNS AT RATED SPEED. 6) AND AGAIN NOTE DOWN THE DIRECTION OF MOTOR. 7) DISCONNECT THE CIRCUIT AFTER FINISHING EXPERIMENT.

OBSERVATIONS :

RESULT AND CONCLUSION:

EXPERIMENT NO. AIM:

DETERMINATION OF VOLTAGE AND CURRENT RATIOS OF SINGLE PHASE TRANSFORMER.

APPRATUS: i)

CONNECTING WIRES,

ii) AMMETER (0-5A) – 2NOS. iii) VOLTMETER (0-300V) – 2NOS. iv) LOAD BANK. vi) AUTOTRANSFORMER.

CIRCUIT DIAGRAM:

FORMULAE: VOLTAGE RATIO = V1/V2, CURRENT RATIO = I1/I2, RELATIONSHIP:

PROCEDURE: 1) CONNECT THE CIRCUIT AS SHOWN IN THE CIRCUIT DIAGRAM USING CONNECTING WIRES AND THE MEASURING INSTRUMENTS. 2) GRADUALLY INCREASE THE VOLTAGE APPLIED TO PRIMARY USING AUTOTRANSFORMER AND SET IT TO ONE LEVEL BY LOOKING AT VOLTMETER. 3) INITIALLY KEEP THE SWITCH OF LOAD BANK OPEN, AT THIS TIME CURRENT WILL BE ZERO. TAKE THE READING OF ALL THE THREE METERS.

4) NOW CLOSE THE SWITCH OF LOAD BANK, AND INCREASE THE LOAD GRADUALLY BY CLOSING ONE SWITCH AT A TIME. 5) EVERY TIME WHEN YOU INCREASE THE LOAD, AJDUST THE PRIMARY SIDE VOLTAGE TO ITS INITIAL VALUE USING AUTOTRANSFORMER. 6) NOTE DOWN THE READING OF ALL THE METERS, EVERY TIME WHEN YOU INCREASE THE LOAD.

7)

CALCULATE THE VOLTAGE AND CURRENT RATIOS.

OBSERVATION TABLE: SR NO.

PRIMARY SIDE VOLTAGE V1 (V)

CURRENT I1 (A)

1 2 3 4 5

CALCULATIONS:

RESULT AND CONCLUSION:

SECONDARY SIDE VOLTAGE V2 (V)

CURRENT I2 (A)

VOLTAGE RATIO, V1/V2

CURRENT RATIO, I1/I1