Danfoss VLT AQUA Drive FC 202 Design Manual

Also see for VLT AQUA Drive FC 202: Service guide Installation guide Installation guide Operating guide Installation guide

Contents

5 Special ConditionsThis section provides detailed data regarding the operatingof the frequency converter in conditions that requirederating. In some conditions, derating is performedmanually. In other conditions, the frequency converterperforms a degree of automatic derating when necessary.Derating ensures proper performance at critical stageswhere the alternative can be a trip.5.1 Manual Derating5.1.1 When to Consider DeratingConsider derating when any of the following conditionsare present:• Operating above 1000 m (low air pressure)• Low-speed operation• Long motor cables• Cables with a large cross-section• High ambient temperatureFor more information, refer to chapter 5.3 Derating forAmbient Temperature.5.1.2 Derating for Running at Low SpeedWhen a motor is connected to a frequency converter, it isnecessary to check that the cooling of the motor isadequate.The level of heating depends on the load on the motor, aswell as the operating speed and time.Constant torque applications (CT mode)A problem may occur at low RPM values in constanttorque applications. In a constant torque application, amotor may overheat at low speeds due to less cooling airfrom the motor integral fan.Therefore, if the motor is to be run continuously at an RPMvalue lower than half the rated value, the motor must besupplied with additional air cooling (or a motor designedfor this type of operation may be used).An alternative is to reduce the load level of the motor byselecting a larger motor. However, the design of thefrequency converter puts a limit on the motor size.Variable (quadratic) torque applications (VT)In VT applications such as centrifugal pumps and fans,where the torque is proportional to the square of thespeed and the power is proportional to the cube of thespeed, there is no need for additional cooling or deratingof the motor.5.1.3 Derating for Low Air PressureThe cooling capability of air is decreased at lower airpressure.Below 1000 m altitude, no derating is necessary. Ataltitudes above 1000 m, dereate the maximum outputcurrent (Iout) at ambient temperature (TAMB) in accordancewith Illustration 5.1. At altitudes above 2000 m, contactDanfoss regarding PELV.Max.Iout (%)at T AMB, MAXAAltitude (km)enclosure B and CenclosureTat 100% I outD100%91%82%0 K-5 K-9 K1 km 2 km 3 km0 K-3.3 K-6 K130BA418.11AMB, MAX (K)Illustration 5.1 Derating of Output Current versus Altitude atTAMB, MAX for Enclosure Sizes A, B and C.An alternative is to lower the ambient temperature at highaltitudes and thereby ensure 100% output current at highaltitudes. As an example of how to read the graph, thesituation at 2000 m is elaborated for an enclosure size Bwith TAMB, MAX = 50 °C. 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 currentis available.Max.Iout (%)at T AMB, MAXD, E and F enclosuresAltitude (km)HO NOTat 100% Iout100%96%92%0 K-3 K-6 K1 km 2 km 3 km-5 K-8 K-11 K130BC015.10AMB, MAXIllustration 5.2 Derating of Output Current versus Altitude atTAMB, MAX for Enclosure Sizes D3h.Special Conditions Design Guide110 Danfoss A/S © 09/2014 All rights reserved. MG20N60255