Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

air-gap line
the line that is obtained by continuing the linear portion of the saturation curve of a synchronous machine or a DC machine. The figure shows a plot of generated voltage vs. field current at constant machine speed. Initially, an increase in field current yields a linear increase in the generated voltage, but as the iron becomes saturated, the voltage rolls off. The air-gap line gives the voltage that would be obtained without saturation.