Electrical Reactance - Phase Relationship

Phase Relationship

The phase of the voltage across a purely reactive device (a device with a resistance of zero) lags the current by radians for a capacitive reactance and leads the current by radians for an inductive reactance. Note that without knowledge of both the resistance and reactance the relationship between voltage and current cannot be determined.

The origin of the different signs for capacitive and inductive reactance is the phase factor in the impedance.

\begin{align} \tilde{Z}_C &= {1 \over \omega C}e^{j(-{\pi \over 2})} = j\left({- \frac{1}{\omega C}}\right) = jX_C \\ \tilde{Z}_L &= \omega Le^{j{\pi \over 2}} = j\omega L = jX_L\quad \end{align}

For a reactive component the sinusoidal voltage across the component is in quadrature (a phase difference) with the sinusoidal current through the component. The component alternately absorbs energy from the circuit and then returns energy to the circuit, thus a pure reactance does not dissipate power.

Read more about this topic:  Electrical Reactance

Famous quotes containing the words phase and/or relationship:

    “The problem of the twentieth century is the problem of the color-line—the relation of the darker to the lighter races of men in Asia and Africa, in America and the islands of the sea. It was a phase of this problem that caused the Civil War.”
    —W.E.B. (William Edward Burghardt)

    “We think of religion as the symbolic expression of our highest moral ideals; we think of magic as a crude aggregate of superstitions. Religious belief seems to become mere superstitious credulity if we admit any relationship with magic. On the other hand our anthropological and ethnographical material makes it extremely difficult to separate the two fields.”
    —Ernst Cassirer (1874–1945)