Impedance in R-L Circuits

Figure 5 Relationship Between Resistance, Reactance, and Impedance

Electrical Science Volume 3 of 4
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Basic AC Reactive Components IMPEDANCE Equation (8-8) is the mathematical representation for the calculation of net reactance when X_C is greater than X_L. X = X_C - X_L (8-8) Impedance is the vector sum of the resistance and net reactance (X) in a circuit, as shown in Figure 5. The angle q is the phase angle and gives the phase relationship between the applied voltage and the current. Impedance in an AC circuit corresponds to the resistance of a DC circuit. The voltage drop across an AC circuit element equals the current times the impedance. Equation (8-9) is the mathematical representation of the voltage drop across an AC circuit. V = IZ (8-9) where V = voltage drop (V) I = current (A) Z = impedance (W) The phase angle q gives the phase relationship between current and the voltage. Impedance in R-L Circuits Impedance is the resultant of phasor addition of R and X_L. The symbol for impedance is Z. Impedance is the total opposition to the flow of current and is expressed in ohms. Equation (8-10) is the mathematical representation of the impedance in an RL circuit. (8-10) Z R² X²_L Example: If a 100 W resistor and a 60 W X_L are in series with a 115V applied voltage (Figure 6), what is the circuit impedance? Rev. 0 Page 11 ES-08

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