Danfoss VLT HVAC Design Manual

Also see for VLT HVAC: Instructions Operating instructions Instruction Operating instructions Instruction manual

Contents

Danfoss VLT HVAC Design Manual Manual pdf 179 page image

8.6 Special Conditions8.6.1 Purpose of DeratingDerating must be taken into account when using the frequency converter at low air pressure (heights), at low speeds, with long motor cables, cableswith a large cross section or at high ambient temperature. The required action is described in this section.8.6.2 Derating for ambient temperature90% 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.8.6.3 Automatic adaptations to ensure performanceThe frequency converter constantly checks for critical levels of internal temperature, load current, high voltage on the intermediate circuit and low motorspeeds. As a response to a critical level, the frequency converter can adjust the switching frequency and / or change the switching pattern in order toensure the performance of the frequency converter. The capability to automatically reduce the output current extends the acceptable operating conditionseven further.8.6.4 Derating for low air pressureThe cooling capability of air is decreased at lower air pressure.Below 1000 m altitude no derating is necessary but above 1000 m the ambient temperature (TAMB) or max. output current (Iout) should be derated inaccordance with the shown diagram.Illustration 8.2: Derating of output current versus altitude at T AMB, MAX for frame sizes A, B and C. At altitudes above 2 km, please contactDanfoss regarding PELV.An alternative is to lower the ambient temperature at high altitudes and thereby ensure 100% output current at high altitudes. As an example of how toread the graph, the situation at 2 km is elaborated. At a temperature of 45° C (TAMB, MAX - 3.3 K), 91% of the rated output current is available. At atemperature of 41.7° C, 100% of the rated output current is available.VLT® HVAC Drive Design Guide 8 General Specifications and TroubleshootingMG.11.B9.02 - VLT® is a registered Danfoss trademark 1798