Magnetic Circuits With Air Gaps.

Energy-conver sion devices which incorporate a moving element have necessarily air gaps in their magnetic circuits.

Air gaps are also pro vide in the magnetic circuits to avoid saturation. A magnetic circuit with an air gap is shown in Fig. (A) An air gap is nothing else but a volume of air between two magnetic surfaces. The length of air gap l, equals the distance between the two magnetic surfaces. The area of X-section of any one of the surfaces gives the air gap area, a When the air-gap length I is much

Magnetic Circuit With Air Gap

smaller than the dimensions of the adjacent core faces, the mag netic flux is constrained essentially to reside in the core and the air gap and is continuous through out the magnetic circuit. Thus the configuration shown in Fig. (A) can be analysed as a magnetic circuit with two series components, a magnetic or iron core of permeability u and mean length l, and an air gap of permeability Ho and length 1g.

Since the permeability of air is constant, the air gap is a linear part of the magnetic circuit and the flux density in the air gap is proportional to the mmf across the air gap.

The necessary mmf is calculated separately for the air gap and the iron portions and then added to determine the total mmf.