Electrical Engineering ⇒ Topic : Fringing

FRINGING

Figure (a) shows a ring provided with an air gap. When flux lines cross the air gap, there is a tendency of flux lines to budge out across the edges of the air gap. This phenomenon is known as fringing. Due to fringing, the effective gap area is larger than that of the ring.

                                              figure (a)

When crossing an air gap, magnetic lines of force tend to bulge out such as lines of force at bb in Figure (a). It is because lines of force repel each other when passing through non-magnetic material such as air. This effect is known as fringing. The result of bulging or fringing is to increase the effective area of air gap and thus decrease the flux density in the gap. The longer the air gap, the greater is the fringing and vice-versa.

                                                              figure (a)

Note. In a short air gap with large cross-sectional area, the fringing may be insignificant. In other situations,10% is added to the air gap's cross-sectional area to allow for fringing