(Approved by AICTE & Affiliated to Calicut University) DEPARTMENT OF ELECTRICAL & ELECTRONICS ENGINEERING : ELECTRICAL MEASUREMENTS AND

Transcription

1 (Approved by AICTE & Affiliated to Calicut University) DEPARTMENT OF ELECTRICAL & ELECTRONICS ENGINEERING ELECTRICAL MEASUREMENTS AND INSTRUMENTATION LAB CLASS SEMESTER SUBJECT CODE SUBJECT : II YEAR (EEE) : IV th SEM (EEE) :EE (P) : ELECTRICAL MEASUREMENTS AND INSTRUMENTATION

2 DEPARTMENT OF ELECTRICAL AND ELECTRONIC ENGINEERING EE09 408(P): ELECTRICAL MEASUREMENTS AND INSTRUMENTATION LAB LIST OF EXPERIMENTS SI.No Name of Experiment Page No 1 MEASUREMENT OF RESISTANCE USING WHEATSTONE BRIDGE 03 2 RESISTANCE MEASUREMENT USING KELVINS DOUBLE BRIDGE 07 3 CALIBRATION OF SINGLE PHASE STATIC ENERGY METER 11 4 CALIBRATION OF SINGLE PHASE ENERGY METER BY PHANTOM LOADING WITHOUT USING PHASE SHIFTING TRANSFORMER 17 5 CALIBRATION OF SINGLE PHASE ENERGY METER BY DIRECT LOADING 23 6 MEASUREMENT OF SELF INDUCTANCE, MUTUAL INDUCTANCE AND COUPLING COEFFICIENT OF TRANSFORMER COILS 27 7 EXTENSION OF RANGE OF WATTMETER USING CT& PT 33 CALIBRATION OF SINGLE PHASE ENERGY METER BY PHANTOM 8 LOADING USING PHASE SHIFTING TRANSFORMER EXTENSION OF RANGE OF AMMETER USING CURRENT TRANSFORMER LINEAR VARIABLE DIFFERENTIAL TRANSFORMER MEASUREMENTS CALIBRATION OF THREE PHASE STATIC ENERGY METER THERMOCOUPLE CHARACTERSTICS RTD CHARACTERISTICS 59

3 Page 1

4 CIRCUIT DIAGRAM Page 2 PORTABLE FORM OF WHEATSTONE BRIDGE

5 Expt No:1 Page 3 MEASUREMENT OF RESISTANCE USING WHEATSTONE BRIDGE Aim To measure the given medium resistances using Wheatstone bridge. Apparatus Required SI.No. NAME OF THE APPRATUS RANGE TYPE QTY 1 Wheat stone Bridge kit Rheostat 15Ω, 5A Wire wound 1 3 Voltmeter 0-30V MC 1 4 Galvanometer DC source Principle The Wheatstone bridge is the most widely used circuit for precisely measuring resistance by the comparison method. The Wheatstone bridge is designed to be used for precision resistance measurements in the laboratory. Values of resistance from to 9,999,000 ohms can be measured with this instrument. When the instrument is used as a Wheatstone bridge, the Ration Multiplier switch allows selection of seven multipliers from to 1,000. Multiplying the reading obtained from the decade dials by the ratio selected yields the value, in ohms, of the unknown resistance. Ratio resistances are accurate to ±0.05%. Procedure The given voltmeter(unknown resistance) is connected to the terminal marked X on the bridge. The toggle switches are adjusted for external battery and galvanometer. An external battery is connected to terminals BB through a rheostat. A galvanometer is connected to the terminals marked GG. on the bridge. The P/Q ratio (Multiplier) is suitably selected. The resistance S is varied by varying the four decade resistances (one at a time starting from the highest range) till null deflection is observed in the galvanometer, when the B and G keys are pressed. Adjustments are made till null deflection is obtained, The reading of the Multiplier and

6 Tabular Column Page 4 Sl.no. Unknown resistance P/Q ratio (multiplier) S 1 (Ω) S 2 (Ω) S 3 (Ω) S 4 (Ω) S =s 1 +s 2 +s 3 +s 4 (Ω) Unknown Resistance X=(p/q)*s (Ω) Sample Calculation =.. S1=.. S2= S3=.. S4=.. S=S1+S2+S3+S4= X=(P/Q)*S=..

7 Page 5 the four dials of the variable resistance S are noted. The readings are tabulated as shown. The experiment is repeated for rheostat instead of voltmeter. Result Measured the given voltmeter using Wheatstone bridge. Resistance of voltmeter =.. Resistance of Rheostat=..

8 CIRCUIT DIAGRAM Page 6 KELVIN DOUBLE BRIDGE

9 Expt No:2 Page 7 RESISTANCE MEASUREMENT USING KELVINS DOUBLE BRIDGE Aim bridge. To measure the resistance of the given ammeter(0-2.5a) using Kelvins double Apparatus Required SI.NO NAME OF THE APPRATUS RANGE TYPE QTY 1 Kelvins Double Bridge D.C source (0-30V) DC 1 3 Ammeter (0-2.5A) MC 1 4 Galvanometer Rheostat 45,5A Wire wound - Principle This method is the best available for precise measurement of low resistances(less than 1). In the figure X is the low resistance to be measured and S is a standard variable resistance of the same order of magnitude, M,Q, p and q are four non-inductive resistances, one pair of which are variable. These are connected to form two sets of ratio arms, which are used for range selection. The ratio Q/M is kept same as q/m ratio along with S being varied till null deflection of the galvanometer is obtained. Procedure Then Connections are made as shown in the figure. Choose a suitable range multiplier. Set the current switch in forward position. Press the galvanometer initial key first and adjust main dial and slide wire to get null deflection in the galvanometer. Then press the galvanometer final

10 Tabular Column Page 8 SI No. Unknown Resistance Remarks Range Multiplier S 1 (mω) S 2 X10-4 (Ω) S=S 1 +S 2 (Ω) X (mω) Mean Resistance (mω) 1 Ammeter+ leads Direct Reverse 2 Leads only Direct Reverse Sample Calculation (Set No..) For Direct: Range multiplier=. S1= S2= S=S1+S2=... X1=(Range Multiplier) X (S)= For Reverse: Range multiplier=. S1= S2= S=S1+S2=... X2=(Range Multiplier) X (S)= Mean Resistance X=(X1+X2)/2=.. Resistance of ammeter= (Resistance of ammeter + leads) - (Resistance of leads alone)=

11 Page 9 key and check whether the galvanometer reads null deflection. If not, adjust the dial readings to get null deflection. The readings of the main dial and slide wire are noted down.the current switch is then put to the reverse position. This reverses the direction of current in circuit. The main dial and slide wire are adjusted to get null deflection and the readings are noted again. The mean of the two is taken as the correct value. This is done to eliminate errors due to thermal effect. The ammeter is then disconnected and the resistance of the connecting leads alone is measured using the same method. The experiment is repeated with different values of range multiplier. The readings are tabulated as shown. Result Resistance of ammeter = (Resistance of ammeter + leads) - (Resistance of leads alone) Measured the resistance of the given ammeter using Kelvins double bridge. Resistance of given ammeter =

12 CIRCUIT DIAGRAM Page 10 Tabular Column SI. No. Volt meter (V) Ammeter (A) Wattmeter (W) Time for 5 Impulses t 1 (s) Time for 1 Impulse t 2 (s) Indicating IR(ws) True Readin g TR (ws) Error IR-TR (ws) %Error

13 Expt No:3 Aim loading. Page 11 CALIBRATION OF SINGLE PHASE STATIC ENERGY METER To calibrate the given single phase static energy meter at unity power factor by direct Apparatus Required SI.NO NAME OF THE APPRATUS RANGE TYPE QTY 1 Autotransformer V Ammeter 0-5A MI 1 3 Voltmeter 0-300V MI 1 4 Wattmeter 250V, 5A UPF 1 5 Energy Meter 240V, 5A 3200 imp/kwhr Static 1 6 Lamp Load - - -

14 Sample Graph Error Curve Page 12 Calibration Curve

15 Principle Page 13 An energy meter is an instrument used to measure electrical energy. It keeps a record of the total energy consumed in a circuit during a particular period. It is an integrating type of instrument. Calibration involves comparing the energy measured by an energy meter with a standard instrument. The standard chosen here is a wattmeter. Since the wattmeter measures only the power, it has to be multiplied with time to get the energy reading. The readings are then compared to find the error in the energy meter. Calibration can be done either by direct loading or phantom loading. In direct loading both the current and pressure coils are fed from the same supply at rated voltage. Energy meters of high rating when tested by direct loading would involve large amount of power. Such meters are thus tested using phantom loading, wherein the pressure coil is supplied from rated supply and current coil circuit from a separate low voltage supply. Procedure Connections are made as shown in the connection diagram. The supply is switched on, keeping the autotransformer in the minimum position. The autotransformer is then varied to get the rated voltage. The lamp load is then switched on and the ammeter reading adjusted for a small value of current. The corresponding readings of voltmeter, ammeter and wattmeter are noted down. The time for five impulse of the energy meter disc is also noted. The experiment is repeated in steps adding loads till the rated current of the energy meter is reached. The true energy and indicated energy is evaluated and the error found out. The error curve and calibration curve are then plotted as shown.

16 Page 14 Sample calculation( Set No ) Energy meter constant k = Voltmeter reading (V ) = Ammeter reading (I) = Time for 5 impulse of energy meter(t 1 )= Time for 5 impulse of energy meter (t 2 )= =.. Indicated energy for 1 impulse of energy meter (IR)= =. Wattmeter reading (W) = True energy for t 2 seconds (TR) = W t 2 = Error = %Error= *100=

17 Result loading. Page 15 Calibrated the given single phase static energy meter at unity power factor by direct

18 Page 16 CIRCUIT DIAGRAM FOR UPF (FIG 1) CIRCUIT DIAGRAM FOR 0.5 LAG/LEAD (FIG 2)

19 Expt No:4 Page 17 CALIBRATION OF SINGLE PHASE ENERGY METER BY PHANTOM Aim LOADING WITHOUT USING PHASE SHIFTING TRANSFORMER transformer To calibrate single phase energy meter by phantom loading without using phase shifting Apparatus Required SI.No. NAME OF THE APPRATUS RANGE TYPE QTY 1 Autotransformer V Single Phase 1 2 Ammeter 0-5A MI 1 3 Voltmeter 0-300V MI 1 4 Wattmeter 300V, 10A UPF 1 5 Energy meter 240V,5-10A Single Phase 1 6 Resistive Load 45Ω, 5A Wire Wound 1

20 Tabular Column For UPF: Page 18 SI No. Voltmeter (V) Ammeter (A) Wattmeter (W) Time for 5 Revolution(t 1 ) (s) Time for 1 Revolution (t 2 ) (s) Indicative IR (W) True TR (W) Error %Error For 0.5 lag: SI No. Voltmeter (V) Ammeter (A) Wattmeter (W) Time for 5 Revolution(t 1 ) (s) Time for 1 Revolution (t 2) (s) Indicative IR (W) True TR (W) Error %Error For 0.5 lead: SI No. Voltmeter (V) Ammeter (A) Wattmeter (W) Time for 5 Revolution(t 1 ) (s) Time for 1 Revolution (t 2) (s) Indicative IR (W) True TR (W) Error %Error

21 Principle Page 19 When a energy meter is designed for high current loads, it is uneconomical to arrange such loads for testing purposes as it involves a considerable waste of time and power. To avoid this problem "phantom loading is done. In phantom loading, pressure coil is excited from normal supply voltage and current coil is excited from a separate low voltage supply. The low impedance of current coil circuit makes it possible to circulate the required current even with low supply voltage. Procedure For testing energy meter at upf condition connections are done as shown in fig 1. Keep the autotransformer position in minimum and loading rheostat position in maximum. Supply is given and apply rated voltage across pressure coil of energy meter and wattmeter. Current in the current coil of the circuit is adjusted by varying auto transformer. First adjust auto transformer to low value of current (say 1A) and increase the current to rated current (say up to 5A). The voltmeter, ammeter, wattmeter and time for 5 revolution of energy meter are noted for various loads current. For a power factor of 0.5, connections are made as shown in figure2. Keep the autotransformer position in minimum. The current coil of wattmeter and energy meter is connected in series to R-phase and pressure coil to Y-phase for lead and B-phase for lag. Supply is given and applies rated voltage across pressure coil of energy meter and wattmeter. If the wattmeter reads negative the pressure coil connections are interchanged. Current in the current coil of the circuit is adjusted by varying auto transformer. First adjust auto transformer to low value of current (say 1A) and increase the current to rated current (say up to 5A). The voltmeter, ammeter, wattmeter and time for 5 revolution of energy meter are noted for various loads current. Calculate indicating reading, true reading, error and %error. Then plot error and calibration curve.

22 Page 20 Sample calculation (Set No..) Energy meter constant k = Voltmeter reading (V ) = Ammeter reading (I) = Time for 5 revolutions of energy meter disc(t 1 )= Time for 5 revolutions of energy meter disc (t 2 )= =.. Indicated energy for 1 revolutions of energy meter disc (IR)= =. Wattmeter reading (W) = True energy for t 2 seconds (TR) = W t 2 = Error = %Error= *100=

23 Result transformer. Page 21 Calibrated single phase energy meter by phantom loading without using phase shifting

24 CIRCUIT DIAGRAM Page 22 Sample Graph Calibration curve Error Curve

25 Expt No:5 Aim Page 23 CALIBRATION OF SINGLE PHASE ENERGY METER BY DIRECT LOADING To calibrate the single phase energy meter by direct loading at unity power factor. Apparatus Required SI.NO NAME OF THE APPRATUS RANGE TYPE QTY 1 Autotransformer V Ammeter 0-5A MI 1 3 Voltmeter 0-300V MI 1 4 Wattmeter 250V, 5A UPF 1 5 Energy Meter 240V, 5A 1800 rev/kwhr Dynamic 1 6 Load - Resistive - Principle In order to check the calibration of a single phase energy meter, the reading of the energy meter is compared with that of a standard instrument. For determining the true energy consumption, a standard wattmeter and an accurate stopwatch is used. From the calculated true energy, the error and the percentage error in the energy meter reading is determined. In direct loading, the current coils of the energy meter and wattmeter are connected to a single phase supply in series with the loading device (say rheostat) whereas the pressure coils are connected directly to the supply. The loading device is adjusted to get the required current. Then the energy consumption is determined by observing the time for a fixed number (say N) of revolutions. The true energy is calculated from the wattmeter reading and the time indicated by the stopwatch.

26 Tabular Column Page 24 SI No. Voltmeter (V) Ammeter (A) Wattmeter (W) Time for 5 Revolution(t 1 ) (s) Time for 1 Revolution (t 2 ) (s) Indicative IR (W) True TR (W) Error %Error Sample calculation (Set No..) Energy meter constant K = Voltmeter reading (V ) = Ammeter reading (I) = Time for 5 revolutions of energy meter disc (t 1 )= Time for 5 revolutions of energy meter disc (t 2 )= =.. Indicated energy for 1 revolutions of energy meter disc (IR)= =. Wattmeter reading (W) = True energy for t 2 seconds (TR) = W t 2 = Error = %Error= *100=

27 Procedure Page 25 The connections are done as shown in the circuit diagram. Adjust the auto transformer to minimum position. Supply is switched on and rated voltage is applied. Remove the loads completely. The current is varied using loading rheostat till the rated current step by step. The ammeter reading, voltmeter reading, wattmeter reading and time for 5 revolutions of energy meter disc are noted in each step. Remove the load step by step. Adjust the auto transformer to minimum position and switch off supply. Result Calibrated the single phase energy meter by direct loading at unity power factor and plotted the graph.

28 CIRCUIT DIAGRAM For Resistance (R): Page 26 Aiding Flux Circuit:

29 Expt No:6 Aim Page 27 MEASUREMENT OF SELF INDUCTANCE, MUTUAL INDUCTANCE AND COUPLING COEFFICIENT OF TRANSFORMER COILS To determine the self inductance, mutual inductance and coupling coefficient of the given iron cored transformer windings. Apparatus Required S.No. Apparatus Range Type Quantity 1 Ammeter (0-0.1)A MI 1 (0-2)A MC 1 2 Voltmeter (0-300)V (0-150V) MI MI 2 1 (0-30V) MC 3 Transformer 1KVA, 230/115V Single phase 1 4 Rheostats 45Ω, 5A Wire Wound 1 5 Auto transformer 230V/(0-270V), single phase Connecting Wires 2.5sq.mm. Copper Few

30 Opposing Flux Circuit: Page 28 Tabular Column For Aiding Flux Circuit: S.No. V A V A1 V A2 I A V A =V A1 +V A2 (V) (V) (V) (A) (V) 1 For Opposing Fux Circuit: S.No. V B (V) V B1 (V) V B2 (V) I B (A) V B =V B1 -V B2 (V) 1

31 Page 29 Principle Inductance is the property of a circuit element by which energy is capable of being stored in a magnetic flux field and any circuit element exhibit the property of inductance is called an inductor. Self Inductance of a coil is the property by which it opposes any flux through it. Mutual inductance of a coil is the ability to produce an emf in the neighbouring coil by induction, when the current in the first coil changes. Consider two magnetically coupled coils of self inductance L1 and L2. Let M be the mutual inductance of the coils connected in series so that flux is produced by current I through the coils are in the same direction, then the effective inductance L A = L 1 + L 2 + 2M If coils are connected such that the flux produced by the current in opposite direction, then effective inductance L B = L 1 + L 2-2M Therefore mutual inductance M= ( L A -L B ) / 4 Coupling coefficient k = M / ((L 1 L 2 ) 1/2 In the first case, if V 1 and I 1 are the applied voltage and current, then Z A =V 1 / I 1, X LA = Z A -R, L A = X LA /(2πf) Similarly for the second case Z B =V 2 / I 2, X LB = Z B -R, L B = X LB /(2πf) L N 230 L N L 1 =4L 2 L L A 2M 5 From the above equations L 1, L 2, M and k can be found out. The experimental determinations of the above parameters are carried out for a pair of transformer winding.

32 Sample Calculation Page 30 For Aiding flux circuit V A =V A1 +V A2 For opposing flux circuit V B =V B1 -V B2 Resistance of transformer winding R =. Applied voltage for aiding circuit V A = Applied current for aiding circuit I A =... Applied voltage for opposing circuit V B = Applied current for opposing circuit I B =... Z A = (V A / I A ) =.. X LA =( Z A 2 -R 2 ) 1/2 = L A = X LA /(2πf)=. Z B = (V B / I B ) =.. X LB = (Z B 2 -R 2 ) 1/2 = L B = X LB /(2πf)=. Mutual inductance M= (L A -L B ) / 4=.. L L A M L 1 =4L 2 =. k = M / (L 1 L 2 ) 1/2 =.

33 Procedure For aiding flux circuit: Page Connections are made as shown in the first figure(aiding flux circuit). 2. Supply is switched on with autotransformer in the minimum position. 3. The autotransformer is adjusted to get the rated voltage in voltmeter V A. 4. The corresponding readings in all meters are noted down. In this case the fluxes produced by both the coils are additive in nature (ie, V A = V A1 + V A2 ). 5. Adjust the auto transformer to minimum position and switch of supply. For opposing flux circuit: 1. Connections are made as shown in the second figure(opposing flux circuit) 2. Supply is switched on with autotransformer in the minimum position. 3. The fluxes produced by the two coils are now in subtractive polarity (ie, V B = V B1 V B2 ). 4. Adjust the auto transformer till the voltmeter V B1 reading equal to V A1 reading of flux aiding circuit. 5. This is done to maintain the same flux in both the cases. 6. The readings of all meters are noted down and tabulated. 7. Adjust the auto transformer to minimum position and switch of supply. Result Determined the self inductance, mutual inductance and coupling coefficient of the given iron cored transformer windings.

34 CIRCUIT DIAGRAM Page 32 Tabular Column SI. Voltmeter Ammeter Voltmetr Ammeter Wattmeter Wattmeter True Error %Error= No. = [(TR- (V 1 ) (A 1 ) (V 2 ) V (A 2 ) (W1) W (W2) W TR= TR- IR)/TR]*100 V A A [Indicative (W 1 /n 1 n 2 IR (IR)] )

35 Expt No:7 Aim (PT) Page 33 EXTENSION OF RANGE OF WATTMETER USING CT& PT To extent range of wattmeter using Current Transformer (CT) and Potential Transformer Apparatus Required SI.No. NAME OF THE APPRATUS RANGE TYPE QTY 1 Autotransformer V Ammeter 0-5A MI A MI 1 3 Voltmeter 0-300V MI V MI 1 4 Wattmeter 300V, 10A UPF 1 150V,5A UPF 1 5 Resistive Load Principle Current transformer (CT) is used for measurement of electric currents. Current transformers, together with voltage transformers (VT) (potential transformers (PT)), are known as instrument transformers. When current in a circuit is too high to directly apply to measuring instruments, a current transformer produces a reduced current accurately proportional to the current in the circuit, which can be conveniently connected to measuring and recording instruments. A current transformer also isolates the measuring instruments from what may be very high voltage in the monitored circuit. Current transformers are commonly used in metering and protective relays in the electrical power industry. Potential transformer or current transformers are used in electrical power system for stepping down the system voltage to a safe value which can be fed to low ratings meters and relays. Commercially available relays and meters used for protection and metering, are designed Sample Calculation (Set No..)

36 CT turn ratio n 1 = PT turn ratio n 2 = V 1 =. I 1 = V 2 =.. I 2 =.. W 1 =.. Page 34 = =.. W 2 =IR=.. TR=(W 1 /n 1 n 2 )= Error=TR-IR=.. %Error= 100 Sample Graph

37 Page 35 for low voltage. A Voltage Transformer theory or Potential Transformer theory is just like theory of general purpose step down transformer. Primary of this transformer is connected across the phases or and ground depending upon the requirement. Just like the transformer, used for stepping down purpose, potential transformer i.e. PT has lowers turns winding at its secondary. The system voltage is applied across the terminals of primary winding of that transformer, and then proportionate secondary voltage appears across the secondary terminals of the PT. The secondary voltage of the PT is generally 110V. In an ideal potential transformer or voltage transformer when rated burden connected across the secondary the ratio of primary and secondary voltages of transformer is equal to the turns ratio and furthermore the two terminal voltages are in precise phase opposite to each other. But in actual transformer there must be an error in the voltage ratio as well as in the phase angle between primary and secondary voltages. Procedure Connections are done as per the circuit diagram. Adjust auto transformer to minimum position. Keep the load in minimum position. Switch on supply. Adjust autotransformer to the rated voltage. Vary the load till the rated current step by step and not down corresponding voltmeters ammeters and wattmeter readings. Then adjust autotransformer to minimum position after removing load. Note down CT and PT ratios. Result Extended the range of wattmeter using current transformer and potential transformer.

38 CIRCUIT DIAGRAM Page 36 Tabular Column SI No. Power factor Voltm eter Readin g (V) Amm eter Read ing (A) Wattmeter (W) Time for 3 Revolution(t 1 ) (s) Time for 1 Revolution (t 2 ) (s) Indicative IR (W) True TR (W) Error %Error Unity 0.6 lead 0.6 lag

39 Expt No:8 Page 37 CALIBRATION OF SINGLE PHASE ENERGY METER BY PHANTOM LOADING USING PHASE SHIFTING TRANSFORMER Aim To calibrate single phase energy meter by phantom loading using phase shifting transformer Apparatus Required SI.NO NAME OF THE APPRATUS RANGE TYPE QTY 1 Autotransformer V Single Phase 1 2 Ammeter 0-5A MI 1 3 Voltmeter 0-250V MI 1 4 Wattmeter 300V, 10A UPF 1 5 Energy meter Phase Shifting 6 Transformer 240V,5-10A Single Phase Resistive Load 45Ω, 5A Wire Wound 1

40 Page 38 Sample Calculation (Set No.) Energy meter constant K = Voltmeter reading (V ) = Ammeter reading (I) = Time for 3 revolutions meter disc(t 1 )= Time for 3 revolutions of energy meter disc (t 2 )= =.. Indicated energy for 1 revolutions of energy meter disc (IR)= =. Wattmeter reading (W) = True energy for t 2 seconds (TR) = W t 2 = Error = %Error= *100= Sample Graph Error Curve Calibration Curve

41 Principle Page 39 Phase shifting transformer is a device is used to obtain different power factor. It consists of laminated silicon steel stator which uses a three phase winding. The rotor is laminated structure having slots in which winding is provided. There is a small gap between the rotor and stator. When the current flows in the stator winding a rotating field is produced. An emf is induced in the rotor. The rotor can be adjusted to any angle. The phase displacement of the rotor emf being equal to angle through which rotor has been moved from the zero position. A scale and the pointer are provided on the top of the instrument to indicate the angle through which the rotor has moved from the zero position. Procedure The connections are done as shown the circuit diagram. Keep the autotransformer in minimum and load in maximum position. Supply is given, and then the voltmeter across the pressure coil of energy meter and wattmeter will show rated voltage. Current in the current coil of the circuit is adjusted by varying autotransformer. The voltmeter, ammeter, wattmeter and time for 3 revolution of energy meter are noted for various loads current. Result Calibrated single phase energy meter by phantom loading using phase shifting transformer

42 CIRCUIT DIAGRAM Page 40 Tabular Column SI. Voltmeter Ammeter Indicative True Error= %Error= No. (A 1 ) IR-TR [(IR- (V) A (IR)=Ammeter (TR) TR)/IR]*100 (A 2 ) A

43 Expt No:9 Aim Page 41 EXTENSION OF RANGE OF AMMETER USING CURRENT TRANSFORMER To extent range of ammeter using Current Transformer (CT) Apparatus Required SI.No. NAME OF THE APPRATUS RANGE TYPE QTY 1 Autotransformer V Ammeter 0-2A MI A MI 1 3 Voltmeter 0-300V MI 1 4 Resistive Load Principle Current transformer (CT) is used for measurement of electric currents. Current transformers, together with voltage transformers (VT) (potential transformers (PT)), are known as instrument transformers. When current in a circuit is too high to directly apply to measuring instruments, a current transformer produces a reduced current accurately proportional to the current in the circuit, which can be conveniently connected to measuring and recording instruments. A current transformer also isolates the measuring instruments from what may be very high voltage in the monitored circuit. Current transformers are commonly used in metering and protective relays in the electrical power industry. Procedure Connections are done as per the circuit diagram. Adjust auto transformer to minimum position. Keep the load in minimum position. Switch on supply. Adjust autotransformer to the rated voltage. Vary the load till the rated current step by step and not down corresponding ammeters readings. Then adjust autotransformer to minimum position after removing load. Note down CT ratios.

44 Page 42 Sample Calculation (Set No..) CT turn ratio n 1 = = V=. Ammeter (A 1 ) = Ammeter (A 2 )=.. True (TR) = Ammeter (A 1 )/n 1 =.. Indicative (IR) = Ammeter (A 2 )=.. Error=IR-TR.. %Error= 100 Sample Graph

45 Result Page 43 Extended the range of ammeter using current transformer.

46 Page 44 LVDT CIRCUIT Sample Graph

47 Expt No:10 Aim Page 45 LINEAR VARIABLE DIFFERENTIAL TRANSFORMER MEASUREMENTS Measuring voltage with displacement variation using Linear Variable Differential Transformer (LVDT). Apparatus Required SI.NO NAME OF THE APPRATUS RANGE TYPE QTY 1 LVDT Voltmeter 0-15V MC 1 Principle The Linear Variable Differential Transformer is a position sensing device that provides an AC output voltage proportional to the displacement of its core passing through its windings. LVDTs provide linear output for small displacements where the core remains within the primary coils. The exact distance is a function of the geometry of the LVDT. An LVDT is much like any other transformer in that it consists of a primary coil, secondary coils, and a magnetic core. An alternating current, known as the carrier signal, is produced in the primary coil. The changing current in the primary coil produces a varying magnetic field around the core. This magnetic field induces an alternating (AC) voltage in the secondary coils that are in proximity to the core. As with any transformer, the voltage of the induced signal in the secondary coil is linearly related to the number of coils. The basic transformer relation is: where, V out is the voltage at the output, V in is the voltage at the input, N out is the number of windings of the output coil, and N in is the number of windings of the input coil.

48 Tabular Column Page 46 SI No. Displacement (cm) Voltage (V)

49 Page 47 As the core is displaced, the number of coils in the secondary coil exposed to the coil changes linearly. Therefore the amplitude of the induced signal varies linearly with displacement. The LVDT indicates direction of displacement by having the two secondary coils whose outputs are balanced against one another. The secondary coils in an LVDT are connected in the opposite sense (one clockwise, the other counter clockwise). Thus when the same varying magnetic field is applied to both secondary coils, their output voltages have the same amplitude but differ in sign. The outputs from the two secondary coils are summed together, usually by simply connecting the secondary coils together at a common center point. At an equilibrium position (generally zero displacement) a zero output signal is produced. The induced AC signal is then demodulated so that a DC voltage that is sensitive to the amplitude and phase of the AC signal is produced. Procedure Connect the LVDT signal conditioner with the power supply of 110 Volts. Set the position of LVDT such that a range of voltage from +10 to -10 volts can be achieved. Change the LVDT displacement and record the voltmeter reading in the table. Plot the graph voltage versus displacement. Result Measured voltage with displacement variation using linear variable differential transformer.

50 CIRCUIT DIAGRAM Page 48

51 Page 49 Exp No:11 CALIBRATION OF THREE PHASE STATIC ENERGY METER Aim To calibrate the given 3-Phase static energy meter at unity power factor by direct loading. Apparatus Required SI.NO NAME OF THE APPRATUS RANGE TYPE QTY 1 Autotransformer 440 V, 6A 3phase 1 2 Ammeter 0-10A MI 1 3 Voltmeter 0-600V MI 1 4 Wattmeter 250V, 10A UPF 1 5 Energy Meter 240V, 10A 3200 imp/kwhr 3 Phase Static Phase Load - Resistive - Principle The conventional mechanical energy meter is based on the phenomenon of Magnetic Induction. It has a rotating aluminium Wheel called Ferriwheel and many toothed wheels. Based on the flow of current, the Ferriwheel rotates which makes rotation of other wheels. This will be converted into corresponding measurements in the display section. Since many mechanical parts are involved, mechanical defects and breakdown are common. More over chances of manipulation and current theft will be higher. Electronic Energy Meter is based on Digital Micro Technology (DMT) and uses no moving parts. So the EEM is known as Static Energy Meter In EEM the accurate functioning is controlled by a specially designed IC called ASIC (Application Specified Integrated Circuit). ASIC is constructed only for specific applications using Embedded System Technology. Similar ASIC are now used in Washing Machines, Air Conditioners, Automobiles, Digital Camera etc.

52 Page 50 Sample Graph Error Curve Calibration Curve Tabular Column SI. No. Volt meter Readin g (V) Amm eter Readi ng (A) Wattmeter (W) W 1 W 2 W 3 W Time for 5 Impulses t 1 (s) Time for 1 Impulses t 2 (s) Indicating IR(ws) True TR (ws) Error IR-TR (ws) %Error

53 Page 51 In addition to ASIC, analogue circuits, Voltage transformer, Current transformer etc are also present in EEM to Sample current and voltage. The Input Data (Voltage) is compared with a programmed Reference Data (Voltage) and finally a Voltage Rate will be given to the output. This output is then converted into Digital Data by the AD Converters (Analogue- Digital converter) present in the ASIC. The Digital Data is then converted into an Average Value. Average Value / Mean Value is the measuring unit of power. The output of ASIC is available as Pulses indicated by the LED (Light Emitting Diode) placed on the front panel of EEM. These pulses are equal to Average Kilo Watt Hour (kwh / unit). Different ASIC with various kwh are used in different makes of EEMs. But usually 800 to 3600 pulses / kwh generating ASIC s are used in EEMs. The output of ASIC is sufficient to drive a Stepper Motor to give display through the rotation of digits embossed wheels. The output pulses are indicated through LED. Procedure Connections are made as shown in the connection diagram. The supply is switched on, keeping the autotransformer in the minimum position. The autotransformer is then varied to get the rated voltage. The load is then switched on and the ammeter reading adjusted for a small value of current. The corresponding readings of voltmeter, ammeter and wattmeter are noted down. The time for three impulse of the energy meter disc is also noted. The experiment is repeated in steps adding loads till the rated current of the energy meter is reached. The true energy and indicated energy is evaluated and the error found out. The error curve and calibration curve are then plotted as shown.

54 Sample Calculations Page 52 Energy meter constant k = Voltmeter reading (V ) = Ammeter reading (I) = Time for 3 impulse of energy meter(t 1 )= Time for 3 impulse of energy meter (t 2 )= =.. Indicated energy for 1 impulse of energy meter (IR)= =. Wattmeter reading (W 1 ) = Wattmeter reading (W 2 ) = Wattmeter reading (W 3 ) = Total wattmeter reading (W) =W 1 +W 2 +W 3 = True energy for t 2 seconds (TR) = W t 2 = Error = %Error= *100=

55 Page 53 Result Calibrated the given three phase static energy meter at unity power factor by direct loading.

56 Circuit Diagram Page 54 Tabular Column SI No. Actual Temperature ( C) Displayed Temperature ( C)

57 Page 55 Exp No :12 Aim THERMOCOUPLE CHARACTERSTICS To study thermocouple characteristics Apparatus Required SI.NO NAME OF THE RANGE TYPE APPRATUS 1 Thermo couple J Type 1 2 Water kettle C Glass 3 Thermometer bead thermom 1 eter QTY 4 Power chord 1 Principle Thermocouple consists of two dissimilar conductors in contact, which produces a voltage when heated. The size of the voltage is dependent on the difference of temperature of the junction to other parts of the circuit. Thermocouples are a widely used type of temperature sensor for measurement and control and can also be used to convert a temperature gradient into electricity. Commercial thermocouples are inexpensive, interchangeable, are supplied with standard connectors, and can measure a wide range of temperatures. In contrast to most other methods of temperature measurement, thermocouples are self powered and require no external form of excitation. The main limitation with thermocouples is accuracy; system errors of less than one degree Celsius ( C) can be difficult to achieve.

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59 Page 57 Any junction of dissimilar metals will produce an electric potential related to temperature. Thermocouples for practical measurement of temperature are junctions of specific alloys which have a predictable and repeatable relationship between temperature and voltage. Different alloys are used for different temperature ranges. Properties such as resistance to corrosion may also be important when choosing a type of thermocouple. Where the measurement point is far from the measuring instrument, the intermediate connection can be made by extension wires which are less costly than the materials used to make the sensor. Thermocouples are usually standardized against a reference temperature of 0 degrees Celsius; practical instruments use electronic methods of cold-junction compensation to adjust for varying temperature at the instrument terminals. Electronic instruments can also compensate for the varying characteristics of the thermocouple, and so improve the precision and accuracy of measurements Procedure Ensure that the power supply and sensor connections made properly and then switch ON the instrument. The display glows to indicate the instrument is ON. Allow the instrument is ON position for initial warm up. Pore around 3/4 th full of water to kettle and place thermocouple sensor inside the kettle. Note down the Initial water temperature from the thermometer. Relay ON, which indicates the relay, is in ON status. Press the INCREMENT/DECREMENT KEY TO SET THE CUTOFF temperature. When the temperature, relay will switch over it shows the LED OFF. Result Measured the temperature using thermo couple method and plotted Temperature vs %Error curve

60 Page 58 RTD Tabular Column SI No. Actual Temperature (TR) ( C) Displayed Temperature (IR) ( C) %Error ( C)

61 Exp. No.13 Aim Page 59 RTD CHARACTERISTICS Measurement of temperature using RTD method and to plot Temperature vs %Error curve Apparatus Required SI.NO NAME OF THE APPRATUS RANGE TYPE QTY 1 ITB-06-CE unit RTD sensor Water bath Multimeter Thermometer C Glass bead thermometer 1 6 Powerchord Principle Resistance temperature detectors, or RTDs, are highly accurate temperature sensors. They are also known for their excellent stability characteristics. They are used to measure temperature from 0 C to 450 C, although some can be used up to 800 C. Due to their low resistance values, you must be careful with the RTD lead resistances. Resistance temperature detectors (RTDs) are made of coils or films of metals (usually platinum). When heated, the resistance of the metal increases; when cooled, the resistance decreases. Passing current through an RTD generates a voltage across the RTD. By measuring this voltage, you determine its resistance, and thus its temperature.

62 Page 60 Sample Calculation (Set no.) Actual Temperature=. Displayed Temperature= %Error= [(Actual Temperature- Displayed Temperature)/Actual temperature]*100=. Sample Graph

63 Page 61 Procedure Adjust the temperature of RTD to room temperature using initial key. Then pour water into the jar attached to the RTD. Boil the water to c. Adjust the final key of RTD to boiling temperature of water. Allow the water to cool. Again reheat the water to boiling temperature. Not down the reading of thermometer and RTD for different temperature and plot the error curve. Result Measured the temperature using RTD method and plotted Temperature vs %Error curve