Special Conditions - Danfoss VLT HVAC Drive FC 100 Series Design Manual

8. General Specifications and Troubleshooting

8.5. Special Conditions

8.5.1. Purpose of derating
Derating must be taken into account when using the frequency converter at low air pressure (heights), at low speeds, with long motor cables, cables
with a large cross section or at high ambient temperature. The required action is described in this section.
8.5.2. Derating for Ambient Temperature
90% frequency converter output current can be maintained up to max. 50 °C ambient temperature.
With a typical full load current of EFF 2 motors, full output shaft power can be maintained up to 50 °C.
For more specific data and/or derating information for other motors or conditions, please contact Danfoss.
8.5.3. Automatic adaptations to ensure performance
The frequency converter constantly checks for critical levels of internal temperature, load current, high voltage on the intermediate circuit and low motor
speeds. As a response to a critical level, the frequency converter can adjust the switching frequency and / or change the switching pattern in order to
ensure the performance of the frequency converter. The capability to automatically reduce the output current extends the acceptable operating conditions
even further.
8.5.4. Derating for Low Air Pressure
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The cooling capability of air is decreased at lower air pressure.
At altitudes higher than 2 km, please contact Danfoss regarding PELV.
Below 1000 m altitude no derating is necessary but above 1000 m the ambient temperature (T
accordance with the shown diagram.
Illustration 8.1: Derating of output current versus altitude at T
An alternative is to lower the ambient temperature at high altitudes and thereby ensure 100% output current at high altitudes.
8.5.5. Derating for Running at Low Speed
When a motor is connected to a frequency converter, it is necessary to check that the cooling of the motor is adequate.
The level of heating depends on the load on the motor, as well as the operating speed and time.
Constant torque applications (CT mode)
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. By altitudes above 2 km, please contact Danfoss regarding PELV.
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VLT HVAC Drive Design Guide
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