The present invention relates to a multi-set switched DC electric machine having conduction ring and brush and having its rotary part of electric machine being installed with an auxiliary excitation winding set, which is served to be driven by the DC power source or by the DC power source rectified from the AC power source, for being connected in series with a magnetic field winding set of electric machine of another electric machine through the auxiliary excitation winding set installed on the rotary part of electric machine, such that the excitation can be variable through altering the current of the magnetic field winding set of electric machine of the another electric machine thereby changing the operational characteristic of the electric machine.