How to calculate three-phase current

Written by nachiket deshmukh
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In electrical engineering, three-phase electric power systems have at least three conductors carrying voltage waveforms, which are 120 degrees offset in time from each other. There are two ways to wire three-phase circuit: the Delta connection, which is a triangle-shaped connection, and the Star connection, which is shaped like a "Y." With the Delta connection, you get lower voltage but more current. In the Star connection, you get higher voltage but less current. Most of the electric power supplied at home and industries is three-phase power because of its power efficiency. Three-phase circuits are used especially in the applications with weight limitations, such as in automobiles. In order to wire three-phase circuits, knowing the physical properties of the circuit like voltage, current and power is necessary.

Skill level:

Things you need

  • Engineering calculator

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  1. 1

    Write down the expression to calculate three-phase circuit amperage (current): I = P / (V * 1.732), where P is the power of the circuit measured in Watts, V is voltage of the circuit measured in Volts and I is current flowing through the circuit measured in Amperes.

  2. 2

    Substitute the values of power and voltage in the three-phase circuit amperage expression: I = P / (V * 1.732). For example, if power is equal to 3000 Watts and voltage is equal to 240 Volts, then substitution of these values results in: I = 3000 / (240 * 1.732) = 7.21 Amperes. Thus, the current for this three-phase circuit is 7.21 Amperes.

  3. 3

    If a phase angle of 60 degrees is specified in a problem, then substitute this value in place of "phi" in the expression: I = P / (V * 1.732 * cosine(phi)). So the expression becomes, I = 3000 / (240 * 1.732 * cosine(60)).

  4. 4

    Calculate the value for cosine(60) using an engineering calculator. Substitute this value in the expression for three-phase circuit amperage calculation. The resulting amperage is: I = 14.43 Amperes.

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