Resistance rotor (electric motor)

This article describes resistance rotors in electric motors. For resistance rotors in turbine construction, especially in wind power plants, see resistance rotors (turbine) .

A resistance rotor is a special squirrel-cage rotor that is installed in three-phase asynchronous motors in order to achieve a certain starting behavior of a motor. Because of its increased slip , it is also known as a slip -on.

Representation of the conductor bars of a squirrel cage, which have an artificially increased electrical resistance in a resistance rotor.

Structure and properties

The groove shape and the structure of the resistance rotor are the same as in the normal squirrel cage rotor. However, the conductor bars of the resistance rotor are made of brass or aluminum alloys. As a result, the rods have a greater ohmic resistance , which remains constant over the entire speed range of the motor. However, the large ohmic resistance, which does not decrease even after the motor has started up, results in relatively large losses. In order to better dissipate the resulting heat loss, motors with resistance rotors have a larger housing than motors with normal squirrel cage rotors.

Operating behavior

Torque characteristic

At the same time, the higher rotor resistance reduces the phase shift , which increases the active power component. The maximum torque shifts to low speeds due to the high effective resistance. Motors with resistance rotors therefore have a high starting torque , which is also the greatest torque that occurs. In addition, the high rotor resistance reduces the starting current . ${\displaystyle M_{A}}$ ${\displaystyle I_{A}}$

However, due to the high effective resistance of the rotor bars, there is a large amount of slippage during operation. However, a large slip has the consequence that the speed behavior is very load-dependent. As a result, motors with slip rotors have a smooth speed behavior without a pronounced breakdown point . Resistance rotors have poor efficiency .

use

Resistance rotors are used for special applications where a smooth speed behavior is desired, e.g. B. Elevators. However, they are only rarely used, since a similar operating behavior can be achieved with normal squirrel cage with additional low-loss electronic devices.

Advantages and disadvantages

advantages

• high starting torque
• low starting current

disadvantage

• high slip
• high losses
• poor efficiency

Source:

literature

• HR Risg: Electrical engineering for the practitioner. 1st edition, Verlag Elektrotechnik Walter Liechti, Aarau (Switzerland) 1990, ISBN 3-905214-11-3

Individual evidence

1. ↑ ^{a b} Hans-Otto Seinsch: Fundamentals of electrical machines and drives. 3rd revised and expanded edition, Springer Fachmedien Wiesbaden, Wiesbaden 1993, ISBN 978-3-519-06164-9 .
2. ^ Hans-Dieter Stölting, Eberhard Kallenbach: Manual electrical small drives. Carl Hanser Verlag, Munich Vienna 2006, ISBN 978-3-446-40019-1 .
3. ↑ ^{a b} Manfred Rudolph, Ulrich Wagner: Energy application technology. Ways and techniques for more efficient energy use, Springer Verlag Berlin-Heidelberg, Berlin 2008, ISBN 978-3-540-79021-1 , pp. 204–205.
4. ^ Günter Springer: Electrical engineering. 18th edition, Verlag Europa-Lehrmittel, Wuppertal, 1989, ISBN 3-8085-3018-9 .
5. ^ Rolf Gloor: Electric Drive Systems (last accessed on October 9, 2012).
6. ^ ^{A b} Germar Müller, Bernd Ponick: Fundamentals of electrical machines. 9th edition, Wiley-VCH Verlag GmbH & Co KGaA., Weinheim 2006, ISBN 3-527-40524-0
7. ↑ Ernst Hörnemann, Heinrich Hübscher: Electrical engineering specialist training in industrial electronics. 1st edition. Westermann Schulbuchverlag GmbH, Braunschweig, 1998, ISBN 3-14-221730-4 .
8. ↑ Manfred Rudolph, Ulrich Wagner: Energy application technology. Springer Verlag, Berlin Heidelberg 2008, ISBN 978-3-540-79021-1 .