Admittance and Susceptance

          Admittance and Susceptance

The discussion for parallel ac circuits will be very similar to that for dc circuits. In dc circuits, conductance (G) was de­fined as equal to 1/R. The total conductance of a parallel circuit was then found by adding the conductance of each branch. The total resistance R_T was then simply 1/G_T.

In ac circuits, we define admittance (Y) as equal to 1/Z. The unit of measure for admittance as defined by the SI system is siemens, which has the symbol S. For many years it was mhos, which had the inverted ohm symbol Ω. Admittance is a measure of how well an ac circuit will admit or allow current to flow in the circuit. The larger its value, therefore, the heavier the current flow for the same applied source of emf. The total admittance of a circuit can also be found by finding the sum of the parallel admittances. The total impedance Z_T of the circuit is then 1/Y_T; that is, for the network