Impedance (Z) is the over-all measure of the ability of a circuit to resist the flow of alternating current under a given a.c. voltage excitation. It may be expressed as Z = V / I where V and I are the a.c. voltage applied to and current flowing through the circuit. Its unit of measurement is the ohm (volt/ampere).
Impedance consists of two components - resistance and reactance. A good understanding of what impedance is and how it is related to resistance and reactance is important in the analysis of voltage-current relationships in an AC circuit that consists of resistors as well as reactive components (capacitors and inductors).
In an AC circuit that consist of a resistance R in series with a reactance X, the following equations apply: |Z| = SQRT(R^2 + X^2); θ = tan^(-1)(X / R) p.f. = cos θ = R / Z where: Z is the impedance of the circuit; R is the resistance of the circuit; X is the reactance of the circuit; θ is the phase angle between the voltage and current signals; and p.f. is the power factors of the circuit, which is the ratio of true power to apparent power of the circuit.
In an AC circuit that consist of a resistance R in parallel with a reactance X, the following equations apply: |Z| = RX / SQRT(R^2 + X^2); θ = tan^(-1)(R / X) p.f. = cos θ = Z/R where: Z is the impedance of the circuit; R is the resistance of the circuit; X is the reactance of the circuit; θ is the phase angle between the voltage and current signals; and p.f. is the power factors of the circuit, which is the ratio of true power to apparent power of the circuit.
The presence of either a capacitor or an inductor (or both) in a circuit produces a phase shift θ between the voltage and current ac signals. This phase shift between voltage and current results in reactive power which can not do real work. In such a case, the true power of the circuit is just a fraction (denoted by the power factor) of its apparent power.
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Impedance (Z) is the over-all measure of the ability of a circuit to resist the flow of alternating current under a given a.c. voltage excitation.
It may be expressed as Z = V / I where V and I are the a.c. voltage applied to and current flowing through the circuit.
Its unit of measurement is the ohm (volt/ampere).
Impedance consists of two components - resistance and reactance. A good understanding of what impedance is and how it is related to resistance and reactance is important in the analysis of voltage-current relationships in an AC circuit that consists of resistors as well as reactive components (capacitors and inductors).
In an AC circuit that consist of a resistance R in series with a reactance X, the following equations apply:
|Z| = SQRT(R^2 + X^2);
θ = tan^(-1)(X / R)
p.f. = cos θ = R / Z
where:
Z is the impedance of the circuit;
R is the resistance of the circuit;
X is the reactance of the circuit;
θ is the phase angle between the voltage and current signals;
and p.f. is the power factors of the circuit, which is the ratio of true power to apparent power of the circuit.
In an AC circuit that consist of a resistance R in parallel with a reactance X, the following equations apply:
|Z| = RX / SQRT(R^2 + X^2);
θ = tan^(-1)(R / X)
p.f. = cos θ = Z/R
where:
Z is the impedance of the circuit;
R is the resistance of the circuit;
X is the reactance of the circuit;
θ is the phase angle between the voltage and current signals;
and p.f. is the power factors of the circuit, which is the ratio of true power to apparent power of the circuit.
The presence of either a capacitor or an inductor (or both) in a circuit produces a phase shift θ between the voltage and current ac signals. This phase shift between voltage and current results in reactive power which can not do real work. In such a case, the true power of the circuit is just a fraction (denoted by the power factor) of its apparent power.
Admittance (Y) is the reciprocal of reactance, i.e., Y = 1 / Z. The unit of measurement for admittance is the siemens (S).
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