Basic AC Reactive Components
IMPEDANCE
Equation (8-8) is the mathematical representation for the calculation of net reactance when XC
is greater than XL.
X = XC - XL
(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 XL. 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
X2L
Example:
If a 100 W resistor and a 60 W XL are in series with a 115V applied voltage
(Figure 6), what is the circuit impedance?
Rev. 0
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