What’s Your Frequency?

October 1, 2013

A question we are often asked is, “Can a motor that is rated for 60 Hz be run at 50 Hz (or vice versa)?” There are several issues that can arise when running a motor at a different frequency than the name plate frequency.

In our previous blog,  AC Motor Basics, we explained the synchronous speed of an AC motor is determined by two factors: the number of poles in the motor and the frequency of the input power to the motor. For a given motor, the number of poles cannot be changed because it is determined by the physical construction of the motor. The frequency of the input power is determined most often by the electrical distribution system in the country that the motor is being operated in. The most common frequencies are 50 Hz and 60 Hz.

Decreasing the frequency on an AC motor decreases its speed. On fan-cooled AC motors, a slower speed can mean the fan doesn’t cool the motor off as well. This could mean that the motor’s continuous rated duty torque will decrease as well. A slower motor also means the rated power of the motor will decrease.

Another important parameter that changes when frequency changes is the ratio of Volts to Hertz. AC motors are designed to operate at a particular V/Hz ratio. In an AC motor, the resistance changes as the frequency changes. If voltage is held constant while resistance decreases, then the current will increase. Increased current may provide more torque but it will also cause more resistive losses in the motor, which may cause the motor to overheat. Similarly, if the voltage is held constant while resistance increases, then the current will decrease. Decreased current means the motor will have less torque. In order to avoid both of these situations, a constant V/Hz ratio should be maintained. This is the principle behind how many variable frequency drives work. By maintaining a constant V/Hz ratio, the current drawn by the motor is kept the same and the motor can maintain torque at varying speeds. It also means that a motor that is rated for 240 VAC, 60 Hz (V/Hz = 240/60 = 4) can be run at 200 VAC, 50 Hz (V/Hz = 200/50 = 4).

Whenever possible a motor should be picked that is rated for the frequency of the power of the country that the motor will operate in. If the motor needs to work at 50 Hz and 60 Hz, many manufacturers, including Groschopp, make motors that are rated at both frequencies. Additionally as we’ve seen above, while it is possible to run a motor at a higher or lower frequency than what it is rated for in certain situations, it is not always practical due to changes in torque, current draw and motor losses.

How to use the Motor Search Tool

Narrow your search by selecting motor type, gearbox, voltage, and phase options for your desired motor.

Select a dominant variable: choose one of the three parameters to narrow your search. The selected variable determines which slider bar you will be able to manually move.

Use the slider corresponding to your dominant variable to further narrow your motor selection. The other sliders will automatically move to show available ranges based on the range of your selected variable.

Results will upload as your search criteria changes. If you have any questions regarding your results or how to use the search tool, you can chat with us using the green tab on the left-hand side of your screen.

Note: Groschopp Universal motors are custom built to fit your application so no additional options are available to narrow the search. Selecting the Universal motor type will prompt a message taking you to the Universal product page.

Not sure what you need?

One of our team members would be happy to help. Contact us at 800-829-4135 or by email at sales@groschopp.com. You can also chat with us using the green tab on the left side of your screen.

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Universal Motors

Groschopp Universal motors are custom built to fit your application so no additional options are available to narrow the search. Standard frame sizes and motor features can be found on the Universal page.

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