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3 PHASE STAR DELTA STAR AND POWER MEASURMENT REPRESENTATION. ANKIT GAMIT ID.NO:13BEEEG120. Introduction. Power may be defined as the rate at which energy is transformed oe made available

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## 3 PHASE STAR DELTA STAR AND POWER MEASURMENT REPRESENTATION

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**3 PHASE STAR DELTA STAR AND POWER MEASURMENT REPRESENTATION**ANKIT GAMIT ID.NO:13BEEEG120**Introduction**• Power may be defined as the rate at which energy is transformed oe made available • In almost all cases the power in a d.c. circuit is best measured by separately measuring quantities, V and I and by computing P=VI • In case of a.c. circuits the instantaneous power varies continuously as the current and voltage go through a cycle of values • The fact that the power factor is involved in the expression for the power means that a wattmeter must be used instead of merely an ammeter and voltmeter.**Wattmeter**• A wattmeter is essentially an inherent combination of an ammeter and a voltmeter and, therefore , consists of two coils known as current coil and pressure coil. • Wattmeter connection:**Wattmeter Errors**• Error due to inductance of pressure coil • Error due to pressure coil capacitance • Error due to Eddy currents : soild metal parts are removed as far away from the current coil as possible**Error due to power loss in pressure coil or current coil**• There are two method of connecting wattmeters in the circuit for measurement of power, as shown in figure below (a) and (b). • Fig (a) : • Fig (b) :**Measurement of Power in Single Phase A.C. Circuit**• 3-voltmeter method • Disadvantages : (i) Even small errors in measurement of voltages may cause serious errors in the value of power, (ii) Supply voltage higher than normal voltage is required**3-Ammeter method**• The disadvantages of measurement of power by 3 voltmeters are overcome in this method**Measurement of power in conjuction with instrument**transformers • This method is used when the currents and voltages of the circuits to be measured are high • Figure below shows a measurement of power with wattmeter in conjunction with instrument transformers in single phase A.C. circuits**Vector diagram for inductive load**• Vector diagram for capasitive load**Measurement of Power in 3-Phase Circuit**• Measurement of power in 3-phase, 4-wire circuits----------- • P=W1+W2+W3 • Measurement of power in 3-phase, 3-wire circuits------------- • P=W1+W2+W3**3-wattmeter method of measuring 3-phase power of delta**connected • P=W1+W2+W3 • 1-wattmeter method of measuring balanced 3-phase power (a) star connected, (b) delta connected • P=3W**2-wattmeter method of measuring 3-phase 3-wire power :**• (a) star connected, • P=W1+W2 • (b) delta connected • P=W1+W2**Determination of P.F. from Wattmeter Reading**• If load is balanced, then p.f. of the load can be determined from the wattmeter readings • Vector diagram for balanced star connected inductive load ----- • The watt-ratio Curve ---------- • p.f. can be determined from reading of two wattmeters

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