The use of frequency converters with fans

If you do not require operating fans with electronic frequency converters or inverters, it is necessary to specify this in the order. Motors are exposed to a considerable load by converters and for this reason they require special design of insulation. When supplied from converters and inverters, magnetic circuits, winding and insulation are subject to strain by the high amplitudes of higher harmonic frequencies, which are products of the pulse width modulation of the output voltage.

Fan starting currents
Depending on the armature design (internal or external, resistor, etc.), output and overall design, starting currents of induction motors used in fans are several times higher than the rated current (about 2x up to 10x). During the operation with a frequency converter (normal fans) or with an inverter (fire safety fans), the starting current has no effect on dimensioning the converter. In most cases, the frequency converters and inverters contain circuits of a “soft” start up. This means that the motor starts running gradually with a reduced voltage and frequency so that the current does exceed the inverter current. The rated motor parameters are usually decisive for dimensioning.

Inverters can be used only with motors that are approved by the manufacturer. Frequency converters cannot be used with high-temperature fans with dependent cooling (bearings, the motor and other components of are not cooled when the fan speed decreases). Always consult the details concerning suitability and safety of converters with the supplier of the converter or inverter and the producer of the fan. The operation of converters, primarily those without filters at the input or, as the case may be, output, can interfere with the operation of other electric or electronic devices or damage them.

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