Example 1, UL (NEC): How to calculate the derated current
The drive type is ACH480-04-014A-4, which has light-duty output current (
I
Ld
) of
14 A at 480 V. Calculate the derated output current at 4 kHz switching frequency,
at 6000 ft altitude and at 131 °F surrounding air temperature.
Switching frequency derating: Derating is not necessary at 4 kHz.
Altitude derating: The derating factor for 6000 ft is
Surrounding air temperature derating: The derating factor for 131 °F surrounding
air temperature is
Multiply the drive output current by all the applicable derating factors. In this
example, the derated output current becomes
Example 2, IEC: How to calculate the required drive
The application requires a nominal motor current of 6.0 A at a switching frequency
of 8 kHz. The supply voltage is 400 V, the altitude is 1800 m and the surrounding
air temperature is 35 °C.
Altitude derating: The derating factor for 1800 m is
Surrounding air temperature derating: Derating is not necessary at 35 °C
surrounding air temperature.
To see if the derated output current of a drive is sufficient for the application,
multiply the nominal output current (
I
n
) by all the applicable derating factors. For
example, drive type ACH480-04-12A7-4 has a nominal output current of 12.6 A at
400 V.
Switching frequency derating: The derating factor for this drive type is 0.68 at
8 kHz. Calculate the derated drive output current:
In this example, the derated output current is sufficient, because it is higher than
the required current.
Example 2, UL (NEC): How to calculate the required drive
The application requires a maximum of 12.0 A of motor current with a 10% overload
for one minute every ten minutes (
I
Ld
) at a switching frequency of 8 kHz. The supply
voltage is 480 V, the altitude is 5500 ft and the surrounding air temperature is
95 °F.
136 Technical data
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