Electrical Machines-Introduction to magnetic circuits-Solved Numericals

Q) A 30cm long circular iron rod is bent into circular ring and 600 turns of windings are wound on it. The diameter of the rod is 20mm and relative permeability of the iron is 4000. A time varying current i=5sin(314.16t) is passed through the winding. Calculate the inductance of the coil and average value of emf induced of the coil.

Ans 1.89V,1890V


2)For the magnetic circuit shown below, calculate the Amp-turn(NI) required to establish a flux of 0.75 wb in the central limb. Given that ur=4000 for the iron core ans-: see below in solution

3) Calculate the net magnetic flux in the core of the following magnetic circuit and show the direction of magnetic flux in the core. Given that cross sectional area of the core is 25 sq.cm and ur=4000.-Ans 23.56 mwb, clockwise

4) A circular iron core has a cross sectional area of 5 sq.cm and mean length of 15cm. It has two coils A and B with 100 turns and 500 turns respectively. The current in the coil A is change from 0 to 10A in 0.1 sec. Calculate the emf induced in the coil B. Given that the relative permeability of the core is 3000.




5) An iron ring of mean length of 1.2m and cross sectional area of 0.005 m² is wound with a coil of 900 turns. If a current of 2A in the coil produces a flux density of 2T in the iron ring. Calculate-:

i) the mmf

ii)total flux in the core

iii) magnetic field strength

iv) relative permeability of the core

Its answers come to be different than that on given solution.

I have tried my best to find all possible ways of solving it. And I hope this method is what it works!

6)An iron ring has a mean length of 1.5m and cross-sectional area of 0.01 m². It has a radial air gap of 4mm. The ring is wound with 250 turns. What dc current would be needed in the coil to produce a flux of 0.8 weber in the air gap. Assume the ur=4000 and leakage factor is 1.25..

7) An uneven ring shaped core(as shown below) has ur=100 and flux density in the larger section is 0.75T. If the current through the coil is 500mA  determine the number of turns in the coil.


8) A magnetic circuit shown below has cast iron core whose dimensions are given below

length(ab+cd)=50 cm

length(ad)=20 cm

length(dea)=50 cm

with respective cross sectional areas.

Determine the current “I” required to produce a magnetic flux of 0.75 mWb in the central limb. Given that:number of turns in the coil=500 and ur=2000.

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