In brief
An electric motor is an electrical machine that converts electrical energy into mechanical rotation via magnetic fields and drives machinery.
Contents
What is Electric motor?
At its core, an electric motor consists of a stationary part, the stator, and a rotating part, the rotor. The interaction of the magnetic fields of the two parts produces torque at the shaft. In industry, three-phase squirrel-cage induction motors predominate because they are robust and low-maintenance. There are also synchronous motors, for example with permanent magnets, DC motors and servo motors for precise positioning and control tasks.
Energy efficiency is classified according to IEC 60034-30-1 into efficiency classes designated IE followed by a digit; a higher digit stands for higher efficiency. In the EU, the Ecodesign Regulation (EU) 2019/1781 sets minimum requirements for many electric motors and variable speed drives. Which class is required in an individual case depends, among other things, on power rating, number of poles and area of application.
For replacement, the nameplate data are decisive: rated power, speed, voltage and connection, frequency, rated current, frame size, mounting arrangement according to the IM code (such as foot or flange mounting), degree of protection and thermal class. If frame size and mounting arrangement match, motors from different sources can often be swapped mechanically, but electrical and thermal data must be checked separately.
In practice: maintenance and procurement
For a spare parts enquiry, a legible photo of the nameplate and details of the mounting arrangement, shaft dimensions and flange are recommended. For older motors, it should be checked whether a new motor of the efficiency class required today fits in terms of frame size and mounting dimensions.
Synonyms and abbreviations: e-motor · three-phase motor · induction motor · asynchronous motor · AC motor
Frequently asked questions
What is the difference between an induction motor and a synchronous motor?
In an induction (asynchronous) motor, the rotor turns slightly more slowly than the stator's rotating field; this slip is necessary to produce torque. In a synchronous motor, the rotor runs exactly in step with the rotating field, for example thanks to permanent magnets. Synchronous motors often achieve higher efficiencies but usually need an inverter to operate. Induction motors, by contrast, can run directly on the mains.
What do the efficiency classes IE1, IE2 and IE3 mean?
The IE classes according to IEC 60034-30-1 describe how efficiently a motor converts electrical into mechanical energy. The higher the digit, the lower the losses. Which minimum class applies in the EU to a particular motor is governed by the Ecodesign Regulation (EU) 2019/1781, depending on power rating and design. In case of doubt, the current version of the regulation provides the answer.
What information is needed to replace an electric motor?
Important are power, speed or number of poles, voltage, frequency, rated current, frame size, mounting arrangement according to the IM code, degree of protection and thermal class. In addition, shaft diameter, flange size and terminal box position are needed. For special versions, for example with a brake, separately driven fan or encoder, these components should also be described.
What does the mounting arrangement IM B3 or IM B5 mean?
The IM code describes the mounting arrangement and type of fixing of a motor. IM B3 stands for a foot-mounted motor with a horizontal shaft, IM B5 for a flange-mounted motor with through holes in the flange. Combinations such as IM B35 denote motors with feet and flange. The correct mounting arrangement is essential so that a replacement motor can be fitted without modification.