ANDERSON S BRIDGE & SCHERING S BRIDGE

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Loren O’Connor’
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1 ANDERSON S BRIDGE & SCHERING S BRIDGE

2 ANDERSON S BRIDGE AIM: A)To measure inductance of a given coil by Anderson s bridge. B) To determine the value of a given capacitor and to obtain for its dissipation factor. APPARATUS: S.NO. Apparatus required Range Type Qty THEORY:

3 CIRCUIT DIAGRAM: ANDERSON'S BRIDGE:- 1KHZ Oscillator L S B D R 1K Ohm C Q 1K Ohm P 1K Ohm SCHERING BRIDGE:- 230V 50Hz S B R 100 Ohm - 10 Ohm C D A D

4 OBSERVATION TABLE: S.NO. P (Ω) Q (Ω) R (Ω) S (Ω) r (Ω) C(mf) L = RC(Q+2r)H S.NO. R 2 (Ω) C 3 ( µ F) R 1 (Ω) C x = C 3 (R 1 / R 2 )

5 PROCEDURE: ANDERSON S BRIDGE: 1. Connect the circuit as per circuit diagram. 2. Keep P/ Q ratio 1 and resistance in branch P should be of resistance R. 3. Now adjust the capacitance value. 4. Adjust r and S such a way to reduce sound. 5. Note down the values P, Q, R, S & r. 6. Repeat the above for different values of C. 7. Calculate self inductance L. SCHERING S BRIDGE: 1. Connect the circuit show. 2. Oscilloscope is connected across points B and D. 3. The bridge is balanced by adjusting C 4 and R The readings are tabulated and C 1 & r 1 are calculated. PRECAUTIONS: 1. Loose connections must be avoided. 2. In unbalanced conditions large current flows through the speaker. 3. Sound should be heard clearly where it is reducing more. 4. The readings are taken without any parallax error. RESULT: Viva Questions: 1) What is the application of Anderson Bridge? 2) What are the advantages and disadvantages of Schering Bridge? 3) What is the application of Schering bride? 4) What is the balancing equation in Schering Bridge? 5) Draw the phasor diagrams for the above two?

6 C.T. TESTING BY SILSBEE S METHOD

7 C.T. TESTING BY SILSBEE S METHOD AIM: To calibrate current transformer by using Silsbee s method. APPARATUS: S.NO. Apparatus required Type Range Qty THEORY:

8 Circuit Diagram:

9 OBSERVATION TABLE: S.NO. I P (A) I SS (A) I SX (A) I (A) W 1 (W) W 2 (W) R X α PROCEDURE: 1. Connect the circuit as per circuit shown. 2. Using the auto T/ F, the current through the primary in gradually increased. 3. The difference b/ w C.T secondaries I should be zero, if it is not zero then connection to any one of C.T secondaries are reversed. 4. The current I p through C.T primaries is made equal to a fixed value using auto T/F. 5. By operating the phase shifter, W 1 is made zero. The readings of ammeter and W 2 are noted. 6. Now, W 1 is adjusted to maximum value by rotating phase shifting T/ F and ammeter and W 2 readings are noted. 7. Above procedure is repeated for different primary current. PRECAUTIONS: 1. Avoid loose connections. 2. Readings to be taken without parallax error.

10 RESULT: Viva Questions: 1) why the C.T & P.T are called instrument transformers? 2) Why we have to close the secondary of a C.T always? 3) What are the different errors in C.T s? 4) What is the procedure to conduct Silsbee s method? 5) Is there any another method to test the C.T? 6) What are the advantages & disadvantages in Silsbee s method?

11 CALIBRATION OF PMMC AMMETER & VOLTMETER BY USING D.C. POTENTIOMETER

12 CALIBRATION OF PMMC AMMETER & VOLTMETER BY USING D.C. POTENTIOMETER AIM: To calibrate the low range Voltmeter, Ammeter and Wattmeter by using D.C. crampton potentiometer. APPARATUS: S.NO. Apparatus required Range Type Qty CIRCUIT DIAGRAM: Circuit is as shown in figure. THEORY:

13 CIRCUIT DIAGRAM:

14 OBSERVATION TABLE: Calibration of Voltmeter: Actual reading (V) True reading (V) % error Calibration of Ammeter: Actual reading (A) True reading (A) % error

15 PROCEDURE: For Standardisation: 1. Connect the circuit as per circuit diagram. 2. Adjust the jockey position on the slide wire nearer to the second terminal of the potentiometer. 3. Apply 10 V from the power supply. 4. By varying the resistance, obtain the zero deflection in the galvanometer. 5. Remove the high resistance from the circuit and again obtain the balance point in galvanometer. 6. Now, the potentiometer is std. against the std.cell. For Calibration of Voltmeter 1. Connect the circuit as per the circuit diagram. 2. Vary the resistance for obtaining the deflection in the voltmeter. 3. Now vary the jockey positions on the slide wire of the potentiometer and obtain the O deflection in the galvanometer. 4. Remove the high resistance from the circuit & obtain exact balancing point. 5. Voltmeter reading Potentiometer reading Calculate % error = 100 Voltmeter reading For Calibration of Ammeter: 1. Connect the circuit as per the circuit diagram. 2. Vary the resistance for obtaining deflection in ammeter. 3. Now vary the jockey positions on the slide wire of the potentiometer and obtain zero deflection in the galvanometer. 4. Remove the high resistance from the circuit and bring obtain the exact balance point. 5. Calculate % error = Ammeter reading Potentiometer reading 100 Ammeter reading 6. Vary the resistance for different values in the Ammeter.

16 For Calibration of Wattmeter: 1. Connect the circuit as per the circuit diagram. 2. Vary the resistance for obtaining deflection in wattmeter. 3. Now vary the jockey positions on the slide wire of the potentiometer and obtain zero deflection in the galvanometer. 4. Remove the high resistance from the circuit and obtain the exact balance point. 5. Calculate % error. 6. Vary the resistance for different values in Wattmeter. GRAPHS: PRECAUTIONS: 1. Connections must be tight. 2. Remove the high resistance and obtain exact balance point. RESULT: Viva Questions: 1) what is the classification in measuring instruments? 2) what are the different errors in PMMC instruments? 3) what are the different errors in MI instruments? 4) what is the procedure to extend the range of meters? 5) By seeing the instrument How do you identify the moving iron instruments? 6) What is the significance Crompton D.C Potentiometer?

17 CALIBRATION OF POWERFACTOR METER

18 CALIBRATION OF POWERFACTOR METER AIM: To calibrate the given power factor meter using Inductive and Capacitive loads. APPARATUS: S.NO. Apparatus required Range Type Qty THEORY:

19 CIRCUIT DIAGRAM:

20 OBSERVATION TABLE: Voltage (V) Current (A) Wattmeter (W) Cos φ Observed Cos φ (actual) Error Tabular form when calibrating used capacitive load: Voltage (V) Current (A) Wattmeter VARS Cos φ Observed Sin φ = W/ V 1. I 1 Actual Cos φ Error

21 PROCEDURE: 1. The circuit is connected as per the circuit diagram in fig.(1). 2. A Rheostat is connected is series with the capacitive load for the single phase. The supply is switched ON. 3. The Voltmeter reading is noted. The load is switched ON in steps and the corresponding values of current, Voltage, Wattmeter and p.f are noted. 4. Now, the supply is switched OFF and is connected as in Fig. (2). 5. The supply is switched ON and steps 3 is repeated. 6. % error is calculated in both the cases. GRAPHS: PRECAUTIONS: 1. Loose connections are to be avoided. 2. Readings should be taken without parallax error. 3. All the connections are checked before starting the experiment. RESULTS: Viva Questions: 1)what is the purpose of controlling, deflecting & damping torque? 2) How do you produce the damping torque in Power factor meter? 3) why the controlling torque is not necessary in p.f meters? 4) what is the construction of p.f meter?

22 CALIBTATION OF WATTMETER BY PHANTOM LOADING

23 CALIBRATION OF WATTMETER BY PHANTOM LOADING AIM: To calibrate the given Wattmeter by Phantom loading. APPARATUS: S.NO. Apparatus required Range Type Qty THEORY:

24 Circuit Diagram:

25 OBSERVATION TABLE: Calibration of U.P.F. Wattmeter: S.No. Volts (V) Amp (A) Watt (W) True Value % error Correction factor Calibration of L.P.F. Wattmeter: S.No. Volts (V) Amp (A) Watt (W) True Value % error Correction factor

26 PROCEDURE: 1. Connect the circuit as per circuit diagram. 2. Apply the rated voltage to the pressure coil and low voltage to the current coil of the Wattmeter. 3. For different values of current through the ammeter measure and record the readings of the voltmeter and ammeter. 4. Repeat the above procedure for different values of voltage applied to the current coil of the Wattmeter. 5. True power = VI (UPF) = VI Cos φ (LPF) 6. Actgual True Calculate % error = 100 True 7. True Actual % correction error factor = 100 True GRAPH: PRECAUTIONS: 1. Readings must be observed with any parallax error. 2. Connections must be tight. 3. Junctions must be avoided at the terminals of voltmeter and ammeter. RESULT: Viva Questions: 1) What is the advantages of phantom loading method? 2) what is the significance of calibration of any meter? 3) what is the construction of wattmeter? 4) What are the different errors occur in wattmeter? 5) What are the different compensating techniques to reduce the errors? 6) What is the significance of multiplication factor?

27 CALIBRATION OF ENERGY METER

28 CALIBRATION OF ENERGY METER AIM: To calibrate energy meter using wattmeter with inductive coil. APPARATUS: S.NO. Apparatus required Range Type Qty THEORY:

29 CIRCUIT DIAGRAM:

30 OBSERVATION TABLE: S.NO. I L (A) No. of rev t (s) W (watt) X4 Actual Reading % error

31 PROCEDURE: 1. Connect the circuit as per the circuit shown. 2. Vary the load in steps and note down ammeter and wattmeter readings. 3. Note down the no. of revolution made of by the energy meters and note down the time taken by using stop watch. 4. By using the energy meter constant, calculate the energy for definite no. of revolutions. Wi Wa 5. % error = 100 W i GRAPH: PRECAUTIONS: 1. Loose connections must be avoided. 2. Readings should be taken without parallax error. 3. Stop watch must be operate properly. RESULT: Viva Questions: 1) what do you mean by creeping? 2) what is meter constant? 3) What are the different errors in energy meters/ 4) what are the compensating methods to reduce the errors? 5)what is the purpose of braking magnet?

32 DETERMINATION OF CHOKE COIL PARAMETERS

33 DETERMINATION OF CHOKE COIL PARAMETERS AIM: To determine the choke coil parameters using 3 ammeter and 3 voltmeter methods. APPARATUS: S.NO. Apparatus required Range Type Qty THEORY:

34 CIRCUIT DIAGRAM:

35 OBSERVATION TABLES: S.NO. A 1 (A) A 2 (A) A 3 (A) Cos φ R (Ω) L (H) V 1 X 0 (Ω) 3 Voltmeter Method: S.NO. V 1 (V) V 2 (V) V 3 (V) COS φ R (Ω) L (H) A (A) X0 (Ω)

36 PROCEDURE: 3 Ammeter Method: 1. Connect the circuit as per the circuit shown. 2. Give the supply of 1 φ 230 V A.C, 50 Hz to variac. 3. Now, by slowly varying the variac note down different values of A 1, A 2 and A Calculate Cos φ = A A2 A 2A A 2 5. Calculate the internal resistance and inductance of the choke coil. 3 Voltmeter Method: 1. Connect the circuit as per the circuit shown Give the supply of 230V, 50 Hz A.C. and note down the value of V 1, V 2 and V 3 by varying the variac. 3. Calculate Cos φ = V V2 V 2V V Calculate the internal resistance and inductance of the choke coil. PRECAUTIONS: 1. Connections must be tight. 2. Readings should be taken without parallax error. 3. Before switch ON supply variac position should be at same voltage. RESULT: Viva Questions: 1) what is the application of chock? 2) What are the parameters in this circuit? 3) Draw the phasor diagram for the two circuits? 4) What is inductance? 5) What is the significance of power factor? 2 3

37 MEASUREMENT OF ACTIVE POWER USING TWO C.T S & ONE WATTMETER

38 MEASUREMENT OF ACTIVE POWER USING TWO C.T S & ONE WATTMETER AIM: To measure the active power of a balanced load. Using single wattmeter and two C.T s. APPARATUS: S.NO. Apparatus required Rating Type Qty THEORY:

39 CIRCUIT DIAGRAM:

40 OBSERVATION TABLE: S.NO. I 1 (A) I 2 (A) I (A) V)V) W(W) W The W Pral. (W) PROCEDURE: 1. Connect the circuit as per the circuit diagram. 2. By adjusting variac, applying 3 - φ voltage to the circuit. 3. Vary the load until the ammeter gives full scale deflection. 4. Read the ammeter in the C.C of wattmeter. 5. This wattmeter reading gives active power consumed by the load. PRECAUTIONS: 1. Connections must be tight. 2. Avoid the parallax error. 3. Before switching ON check fuse ratings. RESULTS: Viva Questions: 1) How many types of powers are there? 2) What is the significance of CT? 3) Why you have to close the secondary of a C.T always? 4) What are the different errors in C.T s? 5) What is the significance of multiplying factor in watt meters?

41 MEASUREMENT OF REACTIVE POWER

42 MEASUREMENT OF REACTIVE POWER AIM: Measuring reactive power of a 3 - φ circuit using single wattmeter. APPARATUS: S.NO. Apparatus required Range Type Qty THEORY:

43 CIRCUIT DIAGRAM:

44 OBSERVATION TABLE: S.NO. V L (V) I L (A) W (watt) 3 W 3 V L I L Sin φ

45 PROCEDURE: 1. Connect the circuit as per circuit diagram. 2. Initially variac should be in minimum position. 3. Close the TPST switch on slowly vary the variac until voltmeter reads line voltage of 415 V. 4. Now apply load in step by step until rated current recommended. 5. Note down the readings of Wattmeter, Voltmeter and Ammeter and tabulate. PRECAUTIONS: 1. Connections must be tight. 2. Readings should be taken without parallax error. RESULT: Viva Questions: 1) what is reactive power? 2) What are the different powers available? 3) What is the difference between balanced load & un balanced load?

46 MEASUREMENTS OF LOW RESISTANCE BY KELVIN S DOUBLE BRIDGE

47 MEASUREMENTS OF LOW RESISTANCE BY KELVIN S DOUBLE BRIDGE AIM: To determine the low resistance by Kelvin s double bridge. S.NO. ITEMS Qty Specifications THEORY:

48 CIRCUIT DIAGRAM:

49 OBSERVATION TABLE: Unknown Resistance 1 P S.NO. P / Q S(Ω) X = S Q Unknown Resistance 2 P S.NO. P / Q S(Ω) X = S Q

50 PROCEDURE: 1. Connect the circuit as per the circuit diagram. 2. Across the terminal R unknown resistance can be measured by ammeter. 3. The ratio P/ Q is adjusted to a particular value. 4. For this ratio, known resistance S is varied until galvanometer shows null deflection and obtain balance bridge conditions for different P/ Q ratio. PRECAUTIONS: 1. Avoid loose connections. 2. Readings must be taken without parallax error. 3. At balance condition galvanometer must read zero deflection. RESULT: Viva Questions: 1) what are the advantages & disadvantages of Kelvin s double bridge? 2) What is the extension in Kelvin s double bridge? 3) What is the application of Kelvin s double bridge?

51 MEASUREMENT OF CAPACITANCE BY SCHERING S BRIDGE

52 MEASUREMENT OF CAPACITANCE BY SCHERING S BRIDGE AIM: To determine the value of a given capacitor and to obtain for its dissipation factor. APPARATUS: S.NO. Apparatus required Range Type Qty THEORY:

53 CIRCUIT DIAGRAM: SCHERING BRIDGE:- 230V 50Hz S B R 100 Ohm - 10 Ohm C D A D

54 OBSERVATION TABLE: S.NO. R 2 (Ω) C 3 ( µ F) R 1 (Ω) C x = C 3 (R 1 / R 2 ) PRECEDURE: 1. Connect the circuit show. 2. Oscilloscope is connected across points B and D. 3. The bridge is balanced by adjusting C 4 and R The readings are tabulated and C 1 & r1 are calculated. PRECAUTIONS: 1. Avoid the loose connections. 2. The readings are taken without any parallax error. RESULT:

ELECTRICAL MEASUREMENTS LAB MANUAL

ELECTRICAL MEASUREMENTS LAB MANUAL Prepared by B.SAIDAMMA R13 Regulation Any 10 of the following experiments are to be conducted 1. Calibration and Testing of single phase energy Meter 2. Calibration of