Electrical Engineering ⇒ Topic : Magnetic leakage and fringing

MAGNETIC LEAKAGE AND FRINGING

Figure (a) shows a magnetised iron ring with a narrow air gap, and the flux which crosses the gap can be regarded as useful flux. Some of the total flux produced by the ring does not cross the air gap, but instead takes a shorter route, as shown in Fig. (a) and is known as leakage flux. The flux while crossing the air gap bulges outwards due to variation in reluctance.

                                                                                                       figure (a)

This is known as  fringing. This is because the lines of force repel each other when passing through the air as a result the flux density in the air gap decreases. For the purpose of calculation it is assumed that the iron carries the whole of the total flux throughout its length. The ratio of total flux to useful flux is called the leakage coefficient or leakage factor.

                                       Leakage factor = Total flux/useful flux.