Overview electrical motors

Electrical motors as energy converter

Electric motors convert electrical energy into mechanical energy. The engine drives a work machine and thus converts electrical energy into mechanical energy. Depending on the voltage, DC and AC machines are used in practice.

Criterias for the selection of an electric motor

  • Power requirement of the working machine
  • operating time and switching frequency
  • Current type, mains voltage and mains frequency
  • Speed and direction of rotation
  • Site and site type

 

motor as an energy converter

The power loss has several reasons:

  • Friction losses in the bearings and eventually the brushes
  • Iron losses due to eddy currents and hysteresis losses
  • Loss of excitation due to changes in the magnetic field
  • Loss of the motor winding (ohmic and inductive resistance)

The efficiency η of an electric motor is given by the ratio of the mechanical output power Pmech (P2) to the electric input power Pelectr. (P1).

ƞ = P2 / P1  and PV = P1 - P2

Four-quadrant operation of electric motors

An engine can act as a motor, when the torque acts in the same direction as the speed (CW or CCW). When torque and speed are opposite, then the motor acts like a brake. With appropriate electronics, this braking energy can be fed back into the grid - keyword "Regenerative Braking".

Four Quandrant Operation of electric motors

Fig.:  Four Quandrant Operation of electric motors