Output of a DC generator is regulated by using a ______ ______ wired in ______ with the magnetic field.

• A. fixed resistors wired in parallel
• B. inductors wired in series
• C. capacitors wired in parallel
• D. variable resistors wired in series

Answer: (D)

To regulate a DC generator’s output, adjust the excitation of the field winding. The generated voltage is mainly determined by the magnetic flux in the field; with a constant speed, increasing the field current strengthens the flux and raises the output, while decreasing the field current weakens the flux and lowers the output. A variable resistor wired in series with the field winding acts as the field control (a field rheostat). By changing that resistance, the regulator changes the field current to maintain the desired voltage. The other options wouldn’t properly control the field current: fixed resistors, inductors, or capacitors in those placements don’t provide the needed, adjustable control of the field excitation.