As an engine, the motor is an essential component of the drive unit. When powering pumps, it is generally supplied with electrical energy, which it converts into kinetic energy. If no electricity is available, transporting units can also be powered by diesel engines or battery-operated electric motors. In each case, the motor performs mechanical work; with respect to pump systems, this means: It drives the pump. An electric motor consists of current flowing through conductor coils that create magnetic fields. The coils are set into motion by the opposing forces of attraction and repulsion. As a drive for pumps, electric motors can generally be classified in two types which, in turn, can be classified in different subtypes: Direct current (DC) motors are available as designs with and without permanent magnet, three-phase alternating current (AC) motors are available as synchronous and asynchronous variant. For both types, the main components consist of a fixed stator and a rotating rotor. For three-phase AC motors, the stator is made up of coil windings in which individual magnetic fields are created, whereas short-circuit currents are created in the rotor, thereby creating a torque and accelerating the rotor. In asynchronous motors, the motor speed and the so-called synchronous speed deviate from each other. In permanent-magnet DC motors, the magnetic field of the stator is created by a permanent magnet. For this reason, no energy is required to generate the magnetic field, which increases efficiency. The variability of the speed is, however, limited. For DC motors without permanent magnet, the stator field is generated by an electromagnet. If the output of a motor can be regulated, it can be adjusted to the demand. When used as a drive for pumps, this allows achieving energy savings since the pump produces only as much output as required for transporting the desired quantity of the medium. Frequency converters can be used in combination with DC as well as three-phase AC motors to generate an adjustable voltage that orients itself by the requirements of the pump and its current load.