Page 500 - Basic Electrical Engineering

Let us consider two magnetic circuits as shown in Fig. 5.18 (a) and (b) and
their equivalent electrical circuits. The equivalence of MMF NI, of the
magnetic circuit is EMF E or V of the electric circuit. Magnetic reluctance of

the iron path and that of air gap are represented by their equivalent
resistances R and R in the electric circuit. Flux in the magnetic circuit is
g
i

represented by current in the electric circuit. The magnetizing force,

produces the flux in the core. The opposition to the flux path is provided by

iron and the air in the air gap through which the flux has to pass. The
reluctance of iron is very low whereas that of air is very high. For a small
amount of air gap, the reluctance will be much more than along the length of

the iron path.
Due to spreading of the flux, the effective area of cross section of the air

gap through which the flux passes increases, which is not desirable. The
fringing effect of flux has been shown in Fig. 5.19.

Figure 5.19 Fringing of flux at the corners of the North pole and South pole of an electrical machine

5.9 ATTRACTIVE FORCE OR THE LIFTING POWER OF ELECTROMAGNETS

An electromagnet is often used to pull or lift iron pieces or objects made of

iron. This is possible due to the energy stored in the magnetic field of the
electromagnet.