Susceptance

In electrical engineering, susceptance (B) is the imaginary part of admittance. The inverse of admittance is impedance, and the real part of admittance is conductance. In SI units, susceptance is measured in siemens. Oliver Heaviside first defined this property, which he called permittance, in June 1887.

The general equation defining admittance is given by

where

The admittance (Y) is the inverse of the impedance (Z)

or

where

Note: The susceptance is the imaginary part of the admittance.

The magnitude of admittance is given by:

Reactance is defined as the imaginary part of Electrical impedance, and is analogous but not generally equal to the inverse of the reactance.
However, for purely-reactive impedances (which are purely-susceptant admittances), the susceptance is equal to negative the inverse of the reactance.
In mathematical notation:

${\displaystyle G=0\iff R=0\iff B=-1/X}$

Note the negation which is not present in the relationship between Electrical resistance and the analogue of conductance G, which = ${\displaystyle \Re (Y)}$.

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