e)High frequency effect

High frequency effect

QUESTION:
What are the derating factors for Contactors at higher frequencies?

ANSWER:
At frequencies equal or higher than 100 Hz the thermal load rating of switchgear is reduced. The reason for this is the so called ''skin effect'' at higher frequencies. This skin effect causes a current flow near the surface of a conductor and not through its full cross section. This effect is increasing with higher frequencies.
As a result the thermal load rating (continuous current) of contactors is reduced according to the following table:
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- at 100 Hz: Ie AC-1 x 0,933
- at 200 Hz: Ie AC-1 x 0,871
- at 300 Hz: Ie AC-1 x 0,836
- at 400 Hz: Ie AC-1 x 0,812
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Note: Above factor applied to Siemens make contactors

Indicated are typical frequencies of practical applications.
Making- and breaking capacities are not reduced within this range.
The contactors are not suitable for frequencies higher than 1000 Hz since internal ferromagnetic parts would be excessively heated by eddy currents



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