Design of dynamos

by Silvanus Phillips Thompson

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1905 ...CHAPTER VI. ESTIMATION OF LOSSES, HEATING, AND PRESSURE-DROP. In this chapter we propose to consider these questions from the designer's point of view, as they are leading features of any design and require to be accurately predetermined from the drawings. On account of the diminishing importance of bipolar machines and of those with smooth core armatures, we shall consider, both in this chapter and the next (which deals with the design of continuous-current machines), the case more particularly of multipolar machines and machines with slotted armatures. The losses occurring in any dynamo or motor come under six heads, as Copper Losses.--These consist of the sum of the C2R losses in armature and series coils (if any) and increase with the load, but are independent of the speed. B. Iron Losses.--These are made up of the eddy-current and hysteresis losses produced in the armature core-plates owing to the changes of flux-density to which they are subjected in each revolution. They vary slightly with the load, and are always variable with the speed. There are also certain losses in the case of machines with toothed armatures due to the production of eddy-currents in the pole-pieces. C. Excitation Losses, that is, the watts expended in heat, in driving the magnetizing current around the magnetizing coils; which losses must be debited against the dynamo, as they lessen the efficiency. D. Commutator Losses.--These consist of--(1) C2R loss on account of contact resistance. (2) Brush friction loss. (3) Losses through sparking, and through eddy-currents in the commutator bars. Of these, Nos. (1) and (2) are as a rule the only ones necessary to consider. There are also local circuits in the brushes producing a small loss of energy. E. Friction and Windage...

336 pages, Paperback

First published August 22, 2015

About the author

Silvanus Phillips Thompson FRS was a professor of physics at the City and Guilds Technical College in Finsbury, England. He was known for his work as an electrical engineer and as an author.

Thompson is one of the individuals represented on the Engineers Walk in Bristol, England.

Thompson was elected a Fellow of the Royal Society in 1891 and was elected a member of the Royal Swedish Academy of Sciences in 1894.