English: A four coil Gramme ring. The coils of A and A' sum together as do the coils of B and B', producing two pulses of power 90 degrees out of phase with each other. When coils A and A' are at maximum output, coils B and B' are at zero output.
Public Domain source:
Hawkins Electrical Guide, Volume 1
Chapter 14: The Dynamo: Current Commutation
Page 177, Figure 185
Copyright 1917 by Theo. Audel & Co.
Printed in the United States
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== Summary == Separate excitation of an electric generator. DC generator with commutation is shown, but the principle also applies to AC alternators. '''Public Domain''' source: * Hawkins Electrical Guide, Volume 1, Page 177. * Copyright 1917 by Theo. Au
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