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Unformatted text preview: 3 1 Experiment 3 Watt, VAR, Volt-Ampere, and Power Factor OBJECTIVE To study the relationship among watt, VAR and volt-ampere. To determine the apparent, active, and reactive power of an inductive load. To improve the power factor of an inductive load. DISCUSSION We now know the following facts: a) Apparent power supplied to a load is the simple product of voltage and current. b) Active power supplied to a load is measured by a wattmeter. When reactive poser is involved, the apparent power is larger than the active power. Reactive power may be inductive or capacitive. In most electromechanical devices, the reactive power will be inductive due to the inductance presented by coils. Reactive power can be calculated by the equation: Reactive power Apparent power Active power (1) If the phase angle between the voltage and current is known, the active power can be found by the equation: Active power V I cos Apparent power cos (2) The ratio of active power to apparent power is called the power factor of an AC circuit. Power factor can be found by the equation: PF P/V I Active power /Apparent power (3) The value of the power factor depends on how much the current and voltage is out of phase. When the current and voltage are in phase, the active is equal to I V, or in other words, the power factor is unity. When current and voltage are out of phase by 90, as in a purely capacitive 3 2 or inductive circuit, the power factor is zero, resulting in a zero value of active power. In circuits containing both resistance and reactance, the value of the power factor is some value between one and zero. If the phase angle between the voltage and current is known, the power factor can be found by the equation: PF cos...
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