Q&A for How to Calculate Power Factor Correction

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  • Question
    What is the reason for calculating the power factor?
    Community Answer
    The power factor is calculated to reduce loading on the source and the physical requirements of the conductors that carry that current. By calculating the power factor, you determine how inefficient your circuit is. This gives you the information you need to make it more efficient by adding in components that will yield power factor correction.
  • Question
    How do I find out how much power my lamp needs?
    Community Answer
    You can get an ammeter and voltmeter and attach them to the lamp wires. If you don't want to do that much work, you can read the instructions in the lamp's package.
  • Question
    How can I increase a power factor?
    Community Answer
    If the circuit is inductive, by adding in a cap bank. If the circuit is capacitive, by adding in inductive loads.
  • Question
    Can you clarify step four?
    Community Answer
    In step four, the user has a right triangle. In the case of a right triangle, the tangent of the angle theta is the opposite (reactive power) divided by the adjacent (real power). Taking the inverse tangent of this ratio gives you the angle (make sure your calculator is in degrees). This angle is the phase difference between your voltage and current.
  • Question
    How do I get the resistance?
    Community Answer
    The resistance is calculated from the real component of the power triangle (a value in watts) and your knowledge of the voltage. R = V^2 / P. R is in ohms, V is in volts and P is in watts.
  • Question
    If the voltage is 120V, the power is 230W, and the power factor is 0.23, then what is the current?
    Jim Coombes
    Community Answer
    PF = P/S which means S=P/PF. S = 230/0.23 = 1000 VA. P = IE which means I = P/E = 1000/120 = 8.33 A.
  • Question
    How do you calculate the required capacitance to increase a low power factor?
    Jim Coombes
    Community Answer
    You need to know the source voltage and frequency, reactive power, real power and power factor goal (for example, 0.93) of the circuit in question then you need to calculate the following: Apparent Power (S) = real power (W) / PF goal. Total Reactive Power (QT) = sqrt(real power ^ 2 apparent power ^ 2. Capacitive Reactive Power (QC) = total reactive power - inductive reactive power. Capactive Reactance (XC) = source voltage ^ 2 / Capacitive Reactive Power. Capacitance (C) = 1 / (2 *pi * frequency * Capacitive Reactance). From this you will have to find the next higher standard capacitor to install.
  • Question
    How do I find a power factor calculator? Is one available?
    Community Answer
    There are many available online. Google "power factor calculator."
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