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Basics: The synchronous motor characteristic

Matthias Beetz, Baumüller Nürnberg GmbH

Read min.

Synchronous motor characteristic

The rotor and the phase sequence in the synchronous motor run synchronously to each other. The advantages range from high efficiency to low maintenance operation. The characteristic describes the relationship between the torque and speed. Multiple characteristics, which represent the different operating modes and physical conditions such as temperature, form the family of characteristics.

The following article covers:


Characteristic is the term used to describe the representation of two physical variables and their relationship to each other in a two-dimensional graph (characteristic curve).

In the case of a synchronous motor, it is the relationship between speed and torque under different conditions.

How is the characteristic of a synchronous motor represented?

The characteristic of a synchronous motor is represented on a two-dimensional graph. The X-axis and Y-axis represent the speed and torque respectively. This allows the dependency between the physical variables to be presented clearly. In general, several lines are shown which together produce the family of characteristics.

The differentiation between different synchronous motor characteristics is due to the varying conditions in practical operation. On the one hand, these are influenced by the temperature and on the other by the type of operation (mode).


Speed and torque - synchronous motor characteristics DSD2-132YZ54A(R)-20-5

Temperature influence

The servo motor has a maximum for the torque. This characteristic for the synchronous motor is named the limit curve and shifts depending on the operating or ambient temperature. The data sheets of the motor manufacturers therefore mostly show the curve for operation of a cold motor and in relation to the motor at operating temperature.

From a certain speed, a further increase causes the torque to drop sharply and produces the voltage limit curve. The type of cooling can shift the characteristic advantageously.

Influence of the operating mode

The intensity of operation of the synchronous motor also influences the characteristic. Where possible, the torque should be kept constant as the speed increases, whereby a loss is unavoidable. At low capacity utilization, a higher torque can be maintained at uniform speed.

Summary: Synchronous motor characteristic

The characteristic of the synchronous motor is the representation of the relationship between speed and torque. The lines can differ significantly at times, depending on the temperature and intensity of operation. Overall, however, it is possible for the user to estimate and plan the power spectrum and the possible applications for their individual use.

Baumüller synchronous motors

When you purchase a three-phase synchronous motor from Baumüller, you acquire a product with high energy efficiency standards and variable cooling options for use in printing and packaging machines as well as, for example, the plastics and textile production sectors.

Do you have any questions?

Matthias Beetz
Training Engineer Academy I Baumüller Nürnberg GmbH

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