The economic aspect of the utilization of permanent magnets in electrical apparatus

The paper first describes the principal types of steels at present available for the production of permanent magnets, and gives magnetic data for typical examples. The cost of these steels is then considered, and figures are given for the actual cost of the material of the steels for which magnetic data have been furnished. Consideration is then given to the other costs involved in working and hardening the steel and housing the finished magnet, and a total figure is obtained which enables a comparison to be made of the various steels under different conditions. It is shown that under certain conditions the use of a cobalt steel will affect an economy over a tungsten or chrome steel, while under other conditions the reverse is the case. Comparison is then made between the cost of providing a given flux by an electromagnet and also by a permanent magnet, allowance being made for the value of the power consumed in the former case. In order to obtain these data an investigation is made of the most economical winding depth of the electromagnet. The result obtained is applied to two typical cases, and it is shown that in small d.c. machinery considerable saving might be effected by the use of permanent fields, particularly, where the cost of fuel is high or where the apparatus runs for long hours, and special applications to certain classes of service are suggested. Finally, some typical examples are considered of the applications of permanent magnets and particularly of cobalt steel magnets, including magnetos, small d.c. generators, alternators, motor-generators, and certain special applications