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# E6_3 - 1 INTRODUCTION 1.1 Objective(1 To measure the power...

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1. INTRODUCTION 1.1 Objective (1) To measure the power consumed and current drawn by a domestic electric fan at various speed settings. (2) To study the significance of power factor and the use of a power correction capacitor to adjust the power factor. 1.2 Theory The instantaneous power consumed in an electric circuit is the product of the instantaneous voltage and current. In linear a.c. circuit, the average power consumed in the circuit is given as : P = IV cos φ  (1) where V = root-mean-square (r.m.s) voltage I = root-mean-square (r.m.s) current φ = phase angle difference between the voltage and current cos φ is defined as the power factor (pf) of the circuit. Hence, to deliver a certain amount of power to a load at a given voltage, the current will be small if the power factor (cos φ ) is high or ideally 1. If the power factor is low, the current will have to be bigger. Such a case is not desirable because we need better and more expensive power transmission cables and equipment to transmit and distribute higher currents. We can therefore see that it is important for electrical appliances to have a high power factor. All common electric motors are inductive loads, causing the current flowing in it to be lagging in phase to that of the voltage. This lagging current can be corrected by connecting a capacitor in parallel with the load as shown in figure 2 & 3 : Energy, Power and Power Factor of A Fan Motor  1 

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The current through a capacitor leads the voltage by 90 ° . The phasor diagram shows that the current thru the capacitor (I C ) causes the angle φ to be smaller and hence the power factor (cos φ ) of the circuit to be bigger. In our experiment, we use a conventional household Energy Meter to measure the power consumed by the fan motor. Average power, P = Energy consumed / time taken = (N/K) x 1000 W t / (60 x 60) = N x 3.6 x 10 6 W K x t  (2) where, K = energy meter constant (number of disc rotations per kWh energy consumed) N = number of rotations by the disc in time t t = time taken for N rotations 1.3 Apparatus and Equipment 3-speed 230V fan Energy, Power and Power Factor of A Fan Motor  2 
The fan used in this experiment has a permanent-capacitor motor. Different tappings in the main winding of the fan motor give three different speeds, which can be selected by the speed selector. 1 Energy (kWh) meter This meter has a voltage coil which is connected across the load and a current coil which is connected in series with the load. Energy consumed in a given time is proportional to the number of rotations by the disc during that time.

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