1. A circular lifting electromagnet has an outside diameter of 1250 mm. The diameter of the inner circular pole is 400 mm and the outer pole has the same area as the inner one. The excitation winding is wrapped around the inner circular pole. The mean length of the magnetic path is 1500 mm. The magnet lifts steel plates of negligible reluctance with an effective air-gap of 6 mm at each pole.
Draw a sketch of the cross-section through the lifting magnet showing the pole faces, magnetic flux path, and exciting winding.
Find the MMF required in the exciting winding when the magnet is used to lift a steel plate of mass 15 000 kg. The magnetisation curve of the electromagnet is given by:
|
H (A/m)
|
400
|
600
|
800
|
1200
|
1600
|
|
B (T)
|
0.81
|
0.98
|
1.1
|
1.24
|
1.35
|