Generally DC generators are classified according to the ways of excitation of their fields. There are three methods of excitation.

  1. Field coils excited by permanent magnets – Permanent magnet DC generators.
  2. Field coils excited by some external source – Separately excited DC generators.
  3. Field coils excited by the generator itself – Self excited DC generators.

How to control the output voltage for the different types of the dc generator and how to reverse the voltage polarity?

  • 3
    \$\begingroup\$ Permanent magnet generators usually don't have field coils. \$\endgroup\$
    – user16324
    Nov 26, 2016 at 17:57

1 Answer 1


The voltage of a permanent-magnet generator must be controlled by controlling the generator speed. The voltage sent to loads could be controlled by sending the voltage first to a voltage regulator or converter. The voltage of a separately-excited DC generator can be controlled by controlling generator speed, by using a variable field supply, or by a combination of both. A self-excited dc generator can be controlled by generator speed or by a rheostat or electronic circuit that reduces the field current. A combination could also be used.


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