Motor / Electric motor

The abbreviation SEW in the name SEW-EURODRIVE stands for "Süddeutsche Elektromotorenwerke" (German for Southern German Electric Motor Plants). Electric motors in various designs still are the basis of our drive technology: From energy-efficient motors, hygienic or explosion-proof designs, linear motors or electric cylinders, we certainly have just the motor solution you need.

What is an electric motor?

How do you bring things in motion and keep them moving without moving a muscle? While steam engines create mechanical energy using hot steam or, more precisely, steam pressure, electric motors use electric energy as their source. For this reason, electric motors are also called electromechanical transducers.

The counter piece to the electric motor is the generator, which has a similar structure. Generators transform mechanic motion into electric power. The physical basis of both processes is the electromagnetic induction. In a generator, current is induced and electrical energy is created when a conductor is within a moving magnetic field. Meanwhile, in an electric motor a current-carrying conductor induces magnetic fields. Their alternating forces of attraction and repulsion create the basis for generating motion.

How does an electric motor work?

Motor housing with stator
Motor housing with stator
Motor housing with stator

In general, the heart of an electric motor consists of a stator and a rotor. The term "stator" is derived from the Latin verb "stare" = "to stand still". The stator is the immobile part of an electric motor. It is firmly attached to the equally immobile housing. The rotor on the contrary is mounted to the motor shaft and can move (rotate).

Cut-away model of a motor on black backdrop
Cut-away model of a motor
Cut-away model of a motor

In case of AC motors, the stator includes the so-called laminated core, which is wrapped in copper wires. The winding acts as a coil and generates a rotating magnetic field when current is flowing through the wires. This magnetic field created by the stator induces a current in the rotor. This current then generates an electromagnetic field around the rotor. As a result, the rotor (and the attached motor shaft) rotate to follow the rotating magnetic field of the stator.

The electric motor serves to apply the created rotary motion in order to drive a gear unit (as torque converter and speed variator) or to directly drive an application as line motor.

What types of electric motors are available?

All inventions began with the DC motor. Nowadays however, AC motors of various designs are the most commonly used electric motors in the industry. They all have a common result: The rotary motion of the motor axis. The function of AC motors is based on the electromagnetic operating principle of the DC motor.

DC motors

As with most electric motors, DC motors consist of an immobile part, the stator, and a moving component, the rotor. The stator consists either of an electric magnet used to induce the magnetic field, or of permanent magnets that continuously generate a magnetic field. Inside of the stator is where the rotor is located, also called armature, that is wrapped by a coil. If the coil is connected to a source of direct current (a battery, accumulator, or DC voltage supply unit), it generates a magnetic field and the ferromagnetic core of the rotor turns into an electromagnet. The rotor is movable mounted via bearings and can rotate so that it aligns with the attracting, i.e. opposing poles of the magnetic field – with the north pole of the armature opposite of the south pole of the stator, and the other way round.

In order to set the rotor in a continuous rotary motion, the magnetic alignment must be reversed again and again. This is achieved by changing the current direction in the coil. The motor has a so-called commutator for this purpose. The two supply contacts are connected to the commutator and it assumes the task of polarity reversal. The changing attraction and repulsion forces ensure that the armature/rotor continues to rotate.

DC motors are mainly used in applications with low power ratings. These include smaller tools, hoists, elevators or electric vehicles.

Asynchronous AC motors

Instead of direct current, an AC motor requires three-phase alternating current. In asynchronous motors, the rotor is a so-called squirrel cage rotor. Turning results from electromagnetic induction of this rotor. The stator contains windings (coils) offset by 120° (triangular) for each phase of the three-phase current. When connected to the three-phase current, these coils each build up a magnetic field which rotates in the rhythm of the temporally offset line frequency. The electromagnetically induced rotor is carried along by these magnetic fields and rotates. A commutator as with the DC motor is not required in this way.

Asynchronous motors are also known as induction motors, as they function only via the electromagnetically induced voltage. They run asynchronously because the circumferential speed of the electromagnetically induced rotor never reaches the rotational speed of the magnetic field (rotating field). Due to this slip, the efficiency of asynchronous AC motors is lower than that of DC motors.

AC synchronous motors

In synchronous motors, the rotor is equipped with permanent magnets instead of windings or conductor rods. In this way the electromagnetic induction of the rotor can be omitted and the rotor rotates synchronously without slip at the same circumferential speed as that of the stator magnetic field. Efficiency, power density and the possible speeds are thus significantly higher with synchronous motors than with asynchronous motors. However, the design of synchronous motors is also much more complex and time-consuming.

Linear motors

In addition to the rotating machines that are mainly used in the industry, drives for movements on straight or curved tracks are also required. Such motion profiles occur primarily in machine tools as well as positioning and handling systems.

Rotating electric motors can also convert their rotary motion into a linear motion with the aid of a gear unit, i.e. they can cause it indirectly. Often, however, they do not have the necessary dynamics to realize particularly demanding and fast "translational" movements or positioning.

This is where linear motors come into play that generate the translational motion directly (direct drives). Their function can be derived from the rotating electric motors. To do this, imagine a rotating motor "opened up": The previously round stator becomes a flat travel distance (track or rail) which is covered. The magnetic field then forms along this path. In the linear motor, the rotor, which corresponds to the rotor in the three-phase motor and rotates in a circle there, is pulled over the travel distance in a straight line or in curves by the longitudinally moving magnetic field of the stator as a so-called carriage or translator.

Who invented the electric motor?

The invention of the electric motor cannot be traced back to a single person. Its discovery was the result of the research of several inventors. In the 19th century the interest in electrical engineering grew more and more and inspired researchers worldwide. One after the other, new inventions came along.

Since the first electric motors were dependent on the current supply of zinc batteries, there was still a long way to go before they could seriously compete with the predominant steam engines. This changed with the development of the first power generators.

But here, too, there were restrictions. The direct current generated by the generators could not be transported over long distances. The breakthrough came only with the introduction of alternating and three-phase current, which could be provided over long distances without great losses, and with the invention of the AC motor.

Here a small, not complete insight into the historical data and facts:

  • In 1800 the Italian professor of physics Alessandro Volta constructed the Voltaic pile named after him. It was able to generate electricity continuously – the first functioning battery consisting of a stack of copper and zinc plates layered on top of each other.
  • 1820: The physical basis for the electric motor is electromagnetism, the discovery of which goes back to the Danish physicist, chemist and natural philosopher Christian Ørsted. He found out that a magnetic field forms around a conductor surrounded by electricity.
  • 1821: The English natural scientist Michael Faraday discovered electromagnetic rotation shortly afterwards. With the aid of a permanent magnet, he set a current-carrying conductor in a rotary motion and thus created the basis for the development of the electric motor.
  • 1822: The Barlow's wheel, named after the English mathematician and physicist Peter Barlow, goes back to his time. He succeeded in turning a device by means of direct current.
  • In 1831, ten years after his discovery of electromagnetic rotation, Michael Faraday successfully carried out an experiment in which he was able to generate electric current with a variable magnetic field. The invention of electromagnetic induction goes back to him and created the conditions for the development of the current generator.
  • In 1831, independently of Faraday, American physicist Joseph Henry discovered electromagnetic induction with his electromagnetically driven oscillating rocker.
  • In 1834, the Prussian-Russian physicist and engineer Moritz Hermann von Jacobi developed the first electric motor suitable for use in real-life practice and thus built the first electrically operated boat, which he continued to improve over the next few years.
  • In 1837, the American goldsmith and inventor Thomas Davenport received the first patent for a DC electric motor developed by him in 1934, which he used to drive his model of an electric locomotive.
  • In 1866, the German industrialist Werner Siemens invented an electric generator based on the principle of the dynamo, which later gave rise to the DC motor.
  • 1888: Nicola Tesla, born in a region of the former Austrian Empire that today is Croatia, and emigrated to America, is the father of many patents, such as several patents regarding the polyphase alternating current.
  • 1888: Almost at the same time, but completely independent from Tesla, the Italian engineer and physics professor Galileo Ferraris delves into the technology of alternating and three-phase current.
  • In 1889, the Russian-born AEG chief design engineer, Michail von Dolivo-Dobrowolsky bases his research on the findings of Tesla and Ferraris, and develops the first three-phase squirrel-cage motor. This has paved the road to success for the asynchronous motor to become commonly used in the industry, and has laid the foundation for building the first current supply systems.

What we offer: The right electric motor for every application from our modular system

Everything started with electric motors. Electric motors are still part of our core business – mainly in form of gearmotors and in conjunction with frequency inverters that match the desired application. As one of the world's leading manufacturers of drive and automation solutions, we offer you a wide range of asynchronous and synchronous motors. Whether energy-efficient motors, linear motors, electric cylinders, motors in hygienic or explosion protection design, extra-low voltage drives, etc. – the optimum electric motor solution for you is guaranteed. A comprehensive range of accessories, such as brakes, built-in encoders, and further options complete our motor range.

AC motors

Servomotors – synchronous and asynchronous

Linear motors

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