IIIRDSEMESTER ELECTRICAL DEPARTMENT OF ELECTRICAL ENGINEERING G.H.RAISONI COLLEGE OF ENGINEERING, NAGPUR Department Of Electrical Engineering IIIRD Sem Electrical Engg. Electrical Measurement & Measuring Instruments Lab ________________________________________________________________________ INDEX Sr. No. 1 2 3 4 5 6 7 8 9 10 11 12 Name of Experiment Page No. Measurement of medium resistance by using Voltmeter Ammeter method. Measurement of medium resistance by using Wheatstone’s bridge. Measurement of high resistance by using loss of charge method. 02 Measurement of low resistance by using Kelvin’s double bridge. Measurement of unknown inductance by using Hay’s bridge. Measurement of unknown inductance by using Owen’s bridge. Measurement of unknown inductance by using Maxwell bridge. Measurement of unknown capacitance by Desauty bridge. Measurement of unknown capacitance by Schering bridge. Measurement of 3-phase power by the onewatt meter method. Measurement of 3-phase power by the two-watt meter method. Measurement of Reactive power in 3- phase circuit by Wattmeter method. 09 G.H.RAISONI COLLEGE OF ENGINEERING, NAGPUR 1 04 07 12 15 17 20 22 24 26 28 IIIRDSEMESTER ELECTRICAL DEPARTMENT OF ELECTRICAL ENGINEERING Experiment No-01 Aim:- Measurement of medium resistance by the Voltmeter , Ammeter method. Apparatus:- DC ammeter(0-50mA) DC Voltmeter (0-50V) Dc power supply (0-30V) Variable Resistance -100 ohm. Connecting wires. Circuit Diagram:- (0-50mA) -+ A (0-50mA) _ + A + (0-30v) V (0-50V) R V (0-30v) - 100 Ohm Fig.(1) (0-50v) R 100 Ohm Fig. (2) Theory: Two types of the connections are done in this method. Ammeter voltmeter method is shown in the figure (2) voltmeter and ammeter are connected in series, where ammeter measures the total current flowing through the circuit and voltmeter measures the voltage across the unknown resistance .The voltmeter should have ideally infinite resistance and ammeter should have ideally zero resistance so that it will measure total current flowing through the unknown resistance. But practically it is not possible and measured value Rm of the resistance is the sum of resistance of ammeter and actual resistance. Rm =R1+Ra Where R1=Actual resistance. Ra=Resistance of the ammeter. It is clear from the expression that the value of measured resistance is equal to actual resistance when ammeter has zero resistance. G.H.RAISONI COLLEGE OF ENGINEERING, NAGPUR 2 1 IIIRDSEMESTER ELECTRICAL DEPARTMENT OF ELECTRICAL ENGINEERING Observation Table:For CASE 1 – voltmeter Ammeter Method Voltage (volt) Current (Amp) Resistance (calculated) Resistance (measured) For CASE 2 – Ammeter voltmeter Method Voltage (volt) Current (Amp) Resistance (calculated) Resistance (measured) Procedure:1) 2) 3) 4) Make the connections as per circuit diagram. Switch on the supply and note down the readings of ammeter and voltmeter. Calculate the value of the unknown resistance by ohms low. Perform the procedure for the other case similarly. Result: - Hence the measured value of the unknown resistance is found to be _________. Viva Questions:1) What are the other methods of measurement of medium resistance? 2) What are the disadvantages of this method? G.H.RAISONI COLLEGE OF ENGINEERING, NAGPUR 3 1 IIIRDSEMESTER ELECTRICAL DEPARTMENT OF ELECTRICAL ENGINEERING Experiment No.-02 Aim: - Measurement of the medium resistance by using wheatstone bridge. Apparatus: Power supply (0-32V D.C) Resistor: - R1=1KΏ, RX=1KΏ, R3=1KΏ, R4=10KΏ. Unknown resistor=100Ώ, Wheatstone bridge kit. Digital multimeter-1no, Patch chords. Circuit Diagram:- d I3 R1 a R3 I1 b G I2 Rx R4 c I4 0-32v G.H.RAISONI COLLEGE OF ENGINEERING, NAGPUR 4 1 IIIRDSEMESTER ELECTRICAL DEPARTMENT OF ELECTRICAL ENGINEERING TheoryWheat stones bridge is very important device used in the measurement of medium resistances. It is an accurate and reliable instrument .The wheat stone bridge is an instrument based on the principle of null indication and comparison measurements . The basic circuit of a wheat stone bridge is shown in fig . it has four resistive arms, consisting of resistances R1,RX,R3 and R4 together with a source of emf and a null detector , usually a galvanometer G or other sensitive current meter is used. The bridge is said to be balanced when there is no current through the galvanometer or when the potential difference across the galvanometer is zero. This occurs when the voltage from point ‘a’ to point ‘d’ equals the voltage from point ‘d’ to point ‘b’ or by referring to other battery terminal, when the voltage from point ‘a’ to point ‘c’ equals the voltage from point ‘c’ to point ‘b’. For bridge balance; I1=I3= E/(R1+R3) (1) I2=I4=E/(RX+R4) (2) E=emf of battery. Combining equ (1) and (2) we get RX*R3=R1*R4 OR RX=(R1*R4)/R3 Where RX is the unknown resistance, R1, R3 and R4 are called the ratio arms. Observation Table: Ratio Arm Resistor R1 R3 Std. Arm Resistor R4 Measured Rx Calculated Rx Procedure: 1) Connect the patch chords as per the circuit diagram. 2) Note the resistance of R1,R4 and R3 using multimeter. G.H.RAISONI COLLEGE OF ENGINEERING, NAGPUR 5 1 IIIRDSEMESTER ELECTRICAL DEPARTMENT OF ELECTRICAL ENGINEERING 3) Switch on the power supply and adjust the resistance R4 such that galvanometer shows the zero deflection. 4) Disconnect the supply & measure the value of RX. 5) Now calculate the value of unknown Resistor R, Using formula Rx=(R1*R4)/R3. Result:- Unknown Resistance found to be __________Ω. Viva Questions: 1) What are the other methods used for measurement of medium resistance? 2) Why we use this method for measurement of medium resistance? G.H.RAISONI COLLEGE OF ENGINEERING, NAGPUR 6 1 IIIRDSEMESTER ELECTRICAL DEPARTMENT OF ELECTRICAL ENGINEERING Experiment No-03 Aim:- Measurement of the high resistance by using loss of charge method. Apparatus:Multimeter –1no Voltmeter –(0-30v)-1no Capacitor-10uf-1no Resister-100K-1no Power supply-(0-30v)-1no . Circuit Diagram:S1 S2 (0-30V) V (0-30V) C=10uf R Theory:In this method the resistance which is measured is connected in parallel with the capacitor C and the electronic voltmeter V. The capacitor is the charged up to some suitable voltage by means of the battery having the voltage V and is then allowed to discharge through the resistance. The terminal voltage is observed over the considerable period of the time during discharge. Let, V=initial voltage on the charged capacitor. v=instantaneous discharging voltage. G.H.RAISONI COLLEGE OF ENGINEERING, NAGPUR 7 1 IIIRDSEMESTER ELECTRICAL DEPARTMENT OF ELECTRICAL ENGINEERING t=the charging time of the capacitor. V=v exp (-t/C*R) or V/v=exp (-t/C*R) or Insulation resistance R=t/(Clog V/v) =0.4343*t/(C log10 V/v) R’=0.4343*t/(C log10 V/v) Where R’ is a resistance of R1 & R in parallel R1 represents the leakage Resistance & R is the unknown resistor. The test is then repeated with the unknown resistance R disconnected & the capacitor discharging through R1 R’=(R*R1)/(R+R1) Observation Table:S. Time (sec) NO. V (withoutR) V(with R) Log10(V/v) without R Log10(V/v) with R Procedure:1) Connections is make as per the circuit diagram. 2) Close the switch S1 and keep S2 open till the capacitor charge upto V volts. 3) Now open the switch S1 & allow the capacitor to discharge by its Owen leakage resistance 4) Note down the reading of the voltmeter verses equal interval of the time. 5) Calculate the unknown resistance using the formula. 6) Now close the switch S1 & S2 till the capacitor charge upto V volts. 7)Now open the switch S1 & allow the capacitor to discharge through the unknown Resistance. Result:- Unknown value of high resistance is calculated by using loss of charge method. Viva Questions:1) Why this method is called as loss of charge method? 2)What kind of errors occurs while performing this practical? G.H.RAISONI COLLEGE OF ENGINEERING, NAGPUR 8 1 IIIRDSEMESTER ELECTRICAL DEPARTMENT OF ELECTRICAL ENGINEERING Experiment No:-04 Aim: - Measurement of the low resistance by using Kelvin’s Double bridge . Apparatus: Regulated dc supply-1no Standard resistance coil-1no Kelvin’s double bridge kit. Digital multimeter-1no, Patch chords. Components Used: Q=q=10KΩ, RX1 =5Ω, RB=11KΩ,, S=Pot of 1kΩ. RX2=10Ω, P=p=100Ω, Circuit Diagram: - b P G Q q d p R S r a m n c R Rb G.H.RAISONI COLLEGE OF ENGINEERING, NAGPUR E 9 1 IIIRDSEMESTER ELECTRICAL DEPARTMENT OF ELECTRICAL ENGINEERING Theory: Kelvin’s bridge is a modification of wheatstone bridge and always used in measurement of low resistance. It uses two sets of ratio arms and the four terminal resistances for the low resistance. As shown in above fig. The first set of ratio P and Q & second set of ratio arms are p and q are used to connect to the galvanometer to a pt ‘d’ at an Approx. potential between points ‘m’ and ‘n’ to eliminate the effects of connecting lead of resistance ‘r’ between the known std. resistance ‘s’ and unknown resistance ‘R’. The ratio P/Q is made equal to p/q. under balanced condition there is no current flowing through galvanometer which means voltage drop between a and b, Eab equal to the voltage drop between a and d, Eamd. Now Eab = Eamd Eab=(P*Eac/P+Q); Eac=I[R+S+[(p+q)r/p+q+r]] ---------(1) Eamd= I[R+ p/p+q[ (p+q)r/p+q+r]] =I[R+p*r/(p+q+r)] ----------------------- (2) For zero deflection-> Eab=Eamd [ P/P+Q]I[R+S+{(p+q)r/p+q+r}]=I[R+pr/p+q+r] --3) Now, if P/Q=p/q Then equa… (3) becomes R=P/Q=S -(4) Equation (4) is the usual working equation. For the Kelvin’s Double Bridge .It indicates the resistance of connecting lead r. It has no effect on measurement provided that the two sets of ratio arms have equal ratios. Equation (3) is useful however as it shows the error that is introduced in case the ratios are not exactly equal. It indicates that it is desirable to keep r as small as possible in order to minimize the error in case there is a diff. between the ratio P/Q and p/q. R=(P*S)/Q Observation Table: P (ratio arm resistor) Q (ratio arm resistor) G.H.RAISONI COLLEGE OF ENGINEERING, NAGPUR Standard resistor S 10 R measured value Calculated R 1 IIIRDSEMESTER ELECTRICAL DEPARTMENT OF ELECTRICAL ENGINEERING Procedure: 1) The circuit configuration on the panel is studied. 2) The unknown resistance is connected as shown. 3) The value of P,Q was selected such that P/Q=p/q 4) S was adjusted for proper balance i.e., galvanometer to shows zero deflection. 5) The value of Unknown Resistance R=(P*S/Q) was calculated. Precautions1) Check all the connections before turning ON the power supply. 2) Note the readings accurately. Result- The observed value of unknown resistance is __________. Viva Questions: 1) Why this method is called as double bridge method? 2) Can this method be beneficial for measurement of low value of Resistance or not? G.H.RAISONI COLLEGE OF ENGINEERING, NAGPUR 11 1 IIIRDSEMESTER ELECTRICAL DEPARTMENT OF ELECTRICAL ENGINEERING Experiment No :-5 Aim: - Measurement of the unknown Inductance by using Hay’s bridge. Apparatus:- Multimeter LCR meter Hay’s bridge kit, Patch cords. Components Used: R2=100Ω, R3= 4.7KΩ, R4= 100Ω, C4= 1uf Circuit Diagram:- E1 E3 D I1 L1 R3 I1 R1 A B G I2 R4 R2 C4 E2 C I2 E4 E G.H.RAISONI COLLEGE OF ENGINEERING, NAGPUR 12 1 IIIRDSEMESTER ELECTRICAL DEPARTMENT OF ELECTRICAL ENGINEERING Observation:R2 = __________. C4 = __________. For Unknown Inductance Lx1:Calculated - Lx1 = (R2R3C4) /(1+ω2R42C42). Lx1 =________mH. Measured - Lx1 = ________mH. Quality factor (Q)=1/ωR4C4. For Unknown Inductance Lx2: Calculated - Lx2 = (R2R3C4) /(1+ω2R42C42). Lx2 =________mH. Measured - Lx2 = ________mH. Quality factor (Q)=ωR4C4. Theory:The hays bridge is the modification of the Maxwell Bridge. This bridge uses a resistance in series with the standard capacitor. The bridge has four resistive arms in which the arms one is consists of the resister R1, Lx .The arm 2 is consists of the variable resistance R3.The low value of the resistance is obtain by the low resistive arms of the bridge. The value of R4 and C4 is the standard value of the capacitor and resistance. By using the unknown inductance having a resistanceR1. R2, R3,R4-is the known non-inductive resistance and C4 is standard value of the capacitor. The unknown value of inductance and Quality factor of the Bridge is obtained by formula. Lx = (R2R3C4) /(1+ω2R42C42) Quality factor (Q)=(1/ωR4C4) 2 For value of Q greater 10, the term (1/Q) will be smaller & hence neglected. Therefore Lx= R2*R3*C4 Basic AC bridges consist of four arms, source excitation and a balanced detector. Commonly used detectors for AC bridges are: (1) Head phones (2) Vibration galvanometers (3) Tunable amplifier detectors Vibration galvanometer is extremely useful at power and low audio frequency ranges. Vibration galvanometers are manufactured to work at various frequency ranging from 5 KHZ to 1 KHZ. But one most commonly used between G.H.RAISONI COLLEGE OF ENGINEERING, NAGPUR 13 1 IIIRDSEMESTER ELECTRICAL DEPARTMENT OF ELECTRICAL ENGINEERING 200HZ. Advantage-1) This Bridge gives very simple expression for unknown for High Q coil. 2) This bridge also gives a simple expression for Q factor. Disadvantage- 1) The hays bridge is suited for the measurement of the High Q inductor. 2) It is used to find the inductor having the q value of the smaller then 10. Procedure:1) Study the circuit provided on the front panel of the kit. 2) Connect unknown inductance LX1 in the circuit. Make all connections to complete the bridge. 3) Put the supply ON 4) Set the null point of galvanometer by adjusting variable resistance R3. 5) Note value of R2, R3, and C4 by removing connection by patch cords. 6) Calculate theoretical value of LX1 using L=R2R3C4 7) Measure value of LX2 by LCR meter and compare it. 8) Repeat process for LX2. Result:- The unknown inductance is measured using Hay’s bridge and is found to be___ Viva Questions:1) What is the Q factor of the coil? 2) Which bridges are used for measurement of inductances? G.H.RAISONI COLLEGE OF ENGINEERING, NAGPUR 14 1 IIIRDSEMESTER ELECTRICAL DEPARTMENT OF ELECTRICAL ENGINEERING Experiment No :-6 Aim:- Measurement of the unknown inductance by using OWEN’S bridge method Apparatus:Digital multimeter, Patch chords. Components used: R3=1K(pot), C4=1uF, R2=1K(pot), L1= L2= -----Galvanometer, 12VAC source. Circuit Diagram:- D R3 R1L1 A B G R2 C4 C2 C Theory:Bridge are used for the accurate measurement of electrical quantities viz; esistance, Capacitance, Inductance, Storage Factor, Loss factor etc. Depending upon the excitations used , the bridge are classified as AC bridges & DC bridges. G.H.RAISONI COLLEGE OF ENGINEERING, NAGPUR 15 1 IIIRDSEMESTER ELECTRICAL DEPARTMENT OF ELECTRICAL ENGINEERING Owen’s – Inductance Capacitance Bridge comes under category of AC bridges and it is used for measurement of an Inductance in terms of capacitance. General form of AC bridges consists of four arms of impedances & AC excitation. Let L1= unknown self inductance of resistance R2=variable non- inductive resistance R3= fixed non- inductive resistance C2=variable standard capacitor C4=fixed standard capacitor And At balance condition, (R1+jwL1) (1/jwC4)=(R2+1/jwC2)*R3 Separating the real & imaginary terms, we obtain: L1=R2R3C4 & R1=R3*C4/C2 Procedure:1. 2. 3. 4. 5. Study the circuit provided on the front panel of the kit. Connect unknown inductance LX1 OR LX2 by patch chords Switch ON power supply By varying the pot R2 & R9 make bridge balance Switch off the power supply, disconnect the patch chords & measure the value of R3 & R2 6. Find the value of unknown inductance by using formula 7. L1=R2R3C4 Observations: Measured value of L Calculated value of L Result:Using Owen’s Bridge we can calculate the value of unknown inductance & we found there is short difference between theoretical and practical value of L. VIVA QUESTIONS:1) Draw the Phaser diagram of OWE’N Bridge? 2) What are the balancing conditions of any a.c. bridge? G.H.RAISONI COLLEGE OF ENGINEERING, NAGPUR 16 1 IIIRDSEMESTER ELECTRICAL DEPARTMENT OF ELECTRICAL ENGINEERING Experiment no 7 Aim:- Measurement of the unknown inductance by using Maxwell’s bridge. Apparatus:Digital multimeter, Patch chords. R2=100Ω, R4=1KΩ, R3=4.7KΩ, C4=1µf, LX2=318mH, LX1=73 mH Circuit Diagram:- D I3 L1 R3 I1 R1 A B G I2 R2 C4 R4 C I4 E Theory:The Maxwell’s bridge is used to measured inductance by comparison with a standard variable capacitance. One of the ratio arms has a résistance and the capacitance in the parallel. In this bridge at the balance condition there is no current flow in the G.H.RAISONI COLLEGE OF ENGINEERING, NAGPUR 17 1 IIIRDSEMESTER ELECTRICAL DEPARTMENT OF ELECTRICAL ENGINEERING galvanometer. At balanced condition, (R1+jwL1) (R4/1+jwC4R4) = R2*R3 By separating the real and imaginary term, the unknown value of the resistor (R1) and the unknown value of the capacitor (C1) has given below. R1= R2*R3/R4 L1= (R2*R3*C4) Observation:R2 = __________. C4 = __________. For Unknown Inductance Lx1:Calculated - Lx1 = (R2R3C4) Lx1 =________mH. Measured - Lx1 = ________mH. Quality factor (Q)=ωR4C4 For Unknown Inductance Lx2: Calculated - Lx2 = (R2R3C4) Lx2 =________mH. Measured - Lx2 = ________mH. Advantage1) This bridge is very useful for measurement of a wide range of a inductance at the power and audio frequencies. 2) The frequency does not appear in any of the two equations. Disadvantage1) This bridge requires a variable standard capacitor, which may be Vary expensive if the calibration to a high degree of the accuracy. 2) The bridge is limited the measure the low Q value. G.H.RAISONI COLLEGE OF ENGINEERING, NAGPUR 18 1 IIIRDSEMESTER ELECTRICAL DEPARTMENT OF ELECTRICAL ENGINEERING Procedure:1) Study circuit on kit from panel. 2) Connect unknown inductance LX1 in circuit. Make all possible connections to complete the network. Switch the supply on. 3) Set null point of galvanometer by adjusting variable resistance R3 4) Note values of R2, R3, C4 by removing their connections. Calculate theoretical values of LX using L1=R2R3C4. 5) Measure actual value of LX1 using LCR meter. Compare this value with calculated. also calculate Q factor by using above equation. Result:- Unknown inductance measured using Maxwell’s bridge is found to be LX1=____ , & LX2 =__---------. ___________ Viva Questions:1) What are the limitations of this bridge? 2) What is the difference between this method and Hays bridge method? G.H.RAISONI COLLEGE OF ENGINEERING, NAGPUR 19 1 IIIRDSEMESTER ELECTRICAL DEPARTMENT OF ELECTRICAL ENGINEERING Experiment no-08 Aim:- Measurement of the unknown capacitance by using De Sauty’s bridge. Apparatus:De Sauty’s bridge kit Digital multimeter, Patch chords, R2=100Ω, R4=10KΩ, R3=10KΩ, C2=1µf, CX1= 1µf, CX2=4.7µf Circuit Diagram:D I3 C1 R3 I1 A B G I2 R4 C2 C I4 E Theory:Bridge are used for the accurate measurement of electrical quantities viz; Resistance, Capacitance, Inductance, Storage Factor, Loss factor etc. Depending upon the excitations used , the bridge are classified as AC bridges & DC bridges. De-sauty Bridge comes under category of AC bridges and it is used for measurement of capacitance. General form of AC bridges consists of four arms of impedances & AC G.H.RAISONI COLLEGE OF ENGINEERING, NAGPUR 20 1 IIIRDSEMESTER ELECTRICAL DEPARTMENT OF ELECTRICAL ENGINEERING excitation. At balanced condition, (1/jwC1) * R4 = (1/jwC2)*R3 Separating real & imaginary part, C1= C2*(R4/R3) Resistance R3 Calculated C1=C2*R4/R3 Measured C1 Procedure: 1) 2) 3) 4) Study the circuit provided on the front panel on the kit. Connect the unknown capacitance of the position given. Set the null point of galvanometer by adjusting the variable resistor R3. Calculate the value of unknown capacitance by formula given Result: -The values of unknown capacitance is measured using De Sauty’s bridge is found to be C1= ______uF. VIVA questions: i) ii) What are the limitation of this bridge? Can Dissipation factor be measured by this bridge? G.H.RAISONI COLLEGE OF ENGINEERING, NAGPUR 21 1 IIIRDSEMESTER ELECTRICAL DEPARTMENT OF ELECTRICAL ENGINEERING Experiment No-09 Aim:- Measurement of the unknown capacitance using schering bridge. Apparatus:- Schearing bridge kit digital multimeter, patch chords, Circuit Diagram:D I3 R1 R3 C1 A I1 B G IC4 I2 C4 C2 C IR4 R4 E Theory:The schering bridge is one of the most important ac bridge used extensively for the measurement of capacitance. In schering bridge the arm 1 contains a series combination of the resistor and the capacitor and standard arm contain only one capacitor. The standard capacitor is usually a standard high quality mica capacitor. In the balance condition of the bridge the sum of the phase angles of the arms 1 G.H.RAISONI COLLEGE OF ENGINEERING, NAGPUR 22 1 IIIRDSEMESTER ELECTRICAL DEPARTMENT OF ELECTRICAL ENGINEERING and 4 is equal the sum of the phase angle of arms 2 and 3.At the balance condition there is no current flow in the galvanometer. At balance condition, [R1+(1/jωC1)] * [R4/(1+jωC4R4)] =R3/( jωC2) After solving & equating real & imaginary parts, we get R1= C4*R3/C2. C1= R4*C2/R3 Observation:R4 = __________. C2 = __________. For Unknown Capacitor C1:Calculated - C1 = (R4*C2/R3) C1 =________. Measured - C1 = ________. Dissipation factor (D.f)=ωR4C4 Procedure: 5) Study the circuit provided on the front panel on the kit. 6) Connect the unknown capacitance of the position given. 7) Set the null point of galvanometer by adjusting the variable resistor R4 8) Calculate the value of unknown capacitance by formula given Result: -The values of unknown capacitance is found to be C1= ______uF. Viva Questions1) What is the Q factor of the coil? 2) Which bridges are used for measurement of inductance G.H.RAISONI COLLEGE OF ENGINEERING, NAGPUR 23 1 IIIRDSEMESTER ELECTRICAL DEPARTMENT OF ELECTRICAL ENGINEERING Experiment no-10 Aim-. Measurement of the 3phase power by the one watt meter method. Apparatus:Three phase variable load. Wattmeter (0-5A)-, 300v-1no Ammeter (0-10A)-1no Voltmeter (0-600v) , (0-300v)-2no Three phase variac. Circuit Diagram:- R (0-5A) A (0-5A,300V) L M C V V (0-300v) 3Phase ,440V, Supply R (100 Ohm,5A) Y R B R (100 Ohm,5A) (100 Ohm,5A) N Theory:In this method the total power consumed is calculated by using one wattmeter . This method is used only if the load is balanced. Current coil is connected in series with one phase ‘R’ & pressure coil of the wattmeter is connected between ‘R’ phase & Neutral of the 3- phase load. Here-V1=V2=V3=V (line voltage) & I1=I2=I3=Line G.H.RAISONI COLLEGE OF ENGINEERING, NAGPUR 24 1 IIIRDSEMESTER ELECTRICAL DEPARTMENT OF ELECTRICAL ENGINEERING &V13-V12=V23 3- phase power = √3* V1*I1*cos θ = 3* Wattmeter Reading (The load is resistive so cos θ=1) Observation Table:Sr no Voltage Current Power 3 phase watt Procedure:1) 2) 3) 4) Make the arrangement as per the circuit diagram. Increase the dimmerstat reading Note the corresponding values of voltmeter ,ammeter and wattmeter. Take consequent 3 readings. Result:- The 3phase Power by one watt meter method is ________Watts. Viva Questions:1) Explain in short how the wattmeter is connected in the circuit to . Measure the power delivered to the Load and the Line. 2) Explain How the Resistive Power is measured by the Wattmeter Method. G.H.RAISONI COLLEGE OF ENGINEERING, NAGPUR 25 1 IIIRDSEMESTER ELECTRICAL DEPARTMENT OF ELECTRICAL ENGINEERING Experiment no- 11 Aim:- Measurement of the 3phase power by the two watt meter method. Apparatus:Ammeter (0-5A)- 1no. Voltmeter (0-600v) –1no Rheostat (100 ohm-5A)-3no Wattmeter (300V-5A) -2no. 3-PHASE dimmerstat connecting wires. Circuit Diagram- 300v,5A R (0-5A) M A C 3-phase, 440V, Supply L V V (0-300v) R Y 100ohm 5A 100ohm 5A R R B N G.H.RAISONI COLLEGE OF ENGINEERING, NAGPUR C V 100ohm 5A L M 300V,5A 26 1 IIIRDSEMESTER ELECTRICAL DEPARTMENT OF ELECTRICAL ENGINEERING Theory:Here two wattmeter are connected to measure power in 3 phase circuit. Let V1,V2,V3 be rms values of phase voltage and i1,i2,i3 be rms values of line current Phase voltage=V1=V2=V3=V Line voltage=V13=V23=V12=√3V Power factor=cos φ Reading of P1 wattmeter =V13*I1cos(30-φ) = √3VIcos(30-φ) Reading of P2 wattmeter= V23*I2cos(30+φ) = √3VI(30+φ) Sum of two wattmeter readings=P=P1+P2 = √3VI[cos( 30-φ)- cos(30+φ)] =3VIcosφ Total Power consumed by the load P= W1+W2. Observation Table:Sr no Voltage Current Power W1 W2 3 phase watt W1+W2 Procedure:1) Make the arrangement as per the circuit diagram. 2) Adjust supply voltage to 100v. Take the reading when the wattmeter is connected between the R and Y phase. 3) Repeat previous for the different reading of the voltage. 4) Also note the corresponding current. 5) Now connect wattmeter between R and B phase . 6) Repeat the previous procedure which will give by the total power consumed by the load. Result:- Hence it is found that the calculated power and the measured power by the two wattmeter method is nearly same. Viva Questions:1) Explain the working of 3phase wattmeter? 2) Explain in short how the wattmeter is connected in the circuit to measure the power delivered to the Load? G.H.RAISONI COLLEGE OF ENGINEERING, NAGPUR 27 1 IIIRDSEMESTER ELECTRICAL DEPARTMENT OF ELECTRICAL ENGINEERING Experiment no- 12 Aim:- Measurement of the 3phase Reactive power by the one watt meter method. Apparatus:Ammeter (0-5A)- 1no. Voltmeter (0-600v) –1no Rheostat (100-5A)-3no 3- phase variable reactive load. 3-PHASE dimmerstat connecting wires. Circuit DiagramR (0-5A) A (0-5A,300V) L M C (0-300v) V 3phase, 440V, Supply V 3-Phase,5A Inductive Load Y B N THEORY:The reactive power in the ckt. Is Q = Visinθ. It is often convenient & essential that reactive power be measured in the given ckt. for load connections & it also serves the check on power factor measerement. Tanθ = REACTIVE POWER / ACTIVE POWER Reactive power in a 3-phase balance ckt. is measured by connecting current coil of wattmeter in one line. & pressure coil across other two lines as shown in above fig. G.H.RAISONI COLLEGE OF ENGINEERING, NAGPUR 28 1 IIIRDSEMESTER ELECTRICAL DEPARTMENT OF ELECTRICAL ENGINEERING Reading of wattmeter = V23* I1 Cos(Φ +90) = -√3V I sin Φ Therefore = V23*I1*Sin Φ. Total reactive power of 3- phase ckt. Q= 3VISin Φ = √3 * wattmeter Reading Observation Table:Sr. no VL IL Power (W) 3-phase Q =√3*Wattmeter Reading Procedure:2. 3. 4. 5. Make the arrangement as per the circuit diagram Adjust the variac to obtain line voltage. Vary the load in such a way that current through phase is equal. Note down the readings. Result:- The reactive power found to be =______. VIVA QUESTION:1) What are the other methods for measurement of Reactive Power? 2) What is the Difference between Active & Reactive Power? G.H.RAISONI COLLEGE OF ENGINEERING, NAGPUR 29 1