FR. CONCEICAO RODRIGUES COLLEGE OF ENGINEERING Department of Electronics Engineering 6. POWER MEASUREMENT BY TWO WATTMETER METHOD 1. Course, Subject & Experiment Details LC RESONANCEEstimated Time Academic Year 2014 – 2015 Course & Semester Chapter No. Experiment Type F.E. (ALL) – Sem. I 3 Hardware Performance 2. . Subject Name Chapter Title Subject Code Experiment No.6 – 02 Hours Basic Electrical and Electronics Engineering Laboratory Three phase circuits FE 105 Aim & Objective of Experiment To measure the power in 3 -phase balanced star and delta connected load and to determine the power factor. 3. Expected Outcome of Experiment This experiment helps students to understand power measurement in 3-phase circuits and to determine the power factor of the given load. 4.Brief Theoretical Description Two wattmeter method is the most suitable method for the power measurement in 3Φ circuits. It is applicable for balanced as well as unbalanced 3Φ load . Power factor can also be determined by this method. IN STAR CONNECTION iR + iY + iB = 0 Where iR, iY, iB are instantaneous currents. iB = -(iR + iY). Instantaneous power P = iRvR + iYvY + iBvB = iRvR + iYvY - (iR + iY)vB. = iR(vR – vB) + iY(vY – vB). = iRvRB + iYvYB. = W1 + W2. Basic Electrical and Electronics Laboratory- Experiment 6 Page 1 FR. CONCEICAO RODRIGUES COLLEGE OF ENGINEERING Department of Electronics Engineering IN DELTA CONNECTION vRY + vYB + vBR = 0 Where vRY, vYB, vBR are instantaneous voltages. VRY = -( vYB + vBR). The instantaneous power P = iRvBR + iYvRY + iBvYB = iRvBR - iY( vYB + vBR) + iBvYB = (iR – iB)vBR + (iB – iY)vYB. = W1 + W2. Thus in both star and delta circuits, the sum of the two wattmeter readings w1 and w2 is equal to the total power consumed in the circuit. Power factor angle is given by formula Φ = tan-1 [√3(w2 – w1)] (w2 + w1) FORMULA: P = √3VLILcos Φ Φ=tan-1[√3(w2 – w1)] (w2 + w1) Basic Electrical and Electronics Laboratory- Experiment 6 Page 2 FR. CONCEICAO RODRIGUES COLLEGE OF ENGINEERING Department of Electronics Engineering 5.r Circuit Diagram & Experimental Setup Figure No.1 Figure No.2 Basic Electrical and Electronics Laboratory- Experiment 6 Page 3 FR. CONCEICAO RODRIGUES COLLEGE OF ENGINEERING Department of Electronics Engineering 6. Apparatus Required 1.Wattmeter 2. 3. 4. 5. 7. 250 V, 5A Ammeter 0 – 2.5 A Voltmeter 0 – 500 V Lamp load Connecting wires. M/I Type M/I type 2 Nos 1Nos Experimental Procedure 1. Connect the circuit as shown in the Figure No1 to measure the power in star connected load. 2. Check the circuit and switch on 3Φ supply switch. 3. Take the readings of the ammeters, voltmeters and wattmeters connected in the circuit. 4. Total power measured is given by (w1 + w2) watts. 5. Calculate the power by formula P = √3VLILcosΦ 6. Compare the two results. 7. Repeat the experiment for different loads. 8. Connect the delta as shown in the Figure No 2. Repeat the procedure for different loads. Basic Electrical and Electronics Laboratory- Experiment 6 Page 4 FR. CONCEICAO RODRIGUES COLLEGE OF ENGINEERING Department of Electronics Engineering 8 Observation Table OBSERVATION TABLE: Lamp load per phase IL VL W1 W2 AMP (V) (WATT) (WATT) P=W1+W2 P=√3VLILc osф STAR CKT DELTA CKT 9 Conclusions & Inferences 100 Post Lab Questions 1.What are the advantages of power measurement by two wattmeter method ? 2.Draw the phasor diagram and prove that sum of two wattmeter reading is equal to 3phase power 3.How to calculate power factor from wattmeter readings? 4.How reactive power can be measured using this method? Basic Electrical and Electronics Laboratory- Experiment 6 Page 5