Danfoss VLT Decentral Drive FCD 302 Design Manual

Also see for vlt fcd 302: Installation guide Operating guide Operating instructions Programming guide Operating guide

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Danfoss VLT Decentral Drive FCD 302 Design Manual Manual pdf 64 page image

To protect the frequency converter against a short circuitat the load sharing and brake outputs, see the designguidelines.Switching on the outputSwitching on the output between the motor and thefrequency converter is fully allowed. No damage to thefrequency converter can occur by switching on the output.However, fault messages can appear.Motor-generated overvoltageThe voltage in the DC link is increased when the motoracts as a generator, in the following cases:• The load drives the motor (at constant outputfrequency from the frequency converter), that is,the load generates energy.• During deceleration (ramp-down), if the inertiamoment is high, the friction is low, and the ramp-down time is too short for the energy to bedissipated as a loss in the frequency converter,the motor, and the installation.• Incorrect slip compensation setting can causehigher DC-link voltage.• Back EMF from PM motor operation. Whencoasted at high RPM, the PM motor back EMF canpotentially exceed the maximum voltagetolerance of the frequency converter and causedamage. The frequency converter is designed toprevent the occurrence of back EMF: The value ofparameter 4-19 Max Output Frequency is automat-ically limited based on an internal calculationbased on the value of parameter 1-40 Back EMF at1000 RPM, parameter 1-25 Motor Nominal Speed,and parameter 1-39 Motor Poles.When motor overspeed is possible (for example,due to excessive windmilling effects), then abrake resistor is recommended.NOTICEThe frequency converter must be equipped with a breakchopper.When possible, the control unit may attempt to correct theramp (parameter 2-17 Over-voltage Control).The inverter turns off when a certain voltage level isreached, to protect the transistors and the DC linkcapacitors.See parameter 2-10 Brake Function and parameter 2-17 Over-voltage Control to select the method used for controllingthe DC-link voltage level.NOTICEOVC cannot be activated when running a PM motor, thatis, for parameter 1-10 Motor Construction set to [1] PMnon-salient SPM.Mains drop-outDuring mains drop-out, the frequency converter keepsrunning until the DC-link voltage drops below theminimum stop level. The minimum stop level is typically15% below the lowest rated supply voltage of thefrequency converter. The mains voltage before the drop-out, combined with the motor load, determines how longit takes for the inverter to coast.Static overload in VVC+ modeWhen the frequency converter is overloaded, the controlsreduce the output frequency to reduce the load. Overloadis defined as reaching the torque limit set inparameter 4-16 Torque Limit Motor Mode/parameter 4-17 Torque Limit Generator Mode.For extreme overload, a current acts to ensure thefrequency converter cuts out after approximately 5–10 seconds.Operation within the torque limit is limited in time (0–60 seconds) in parameter 14-25 Trip Delay at Torque Limit.3.4.4.1 Motor Thermal ProtectionTo protect the application from serious damage, thefrequency converter offers several dedicated features:Torque limitThe torque limit feature protects the motor from beingoverloaded independent of the speed. Select torque limitsettings in parameter 4-16 Torque Limit Motor Mode and/orparameter 4-17 Torque Limit Generator Mode. Set the timeto trip for the torque limit warning in parameter 14-25 TripDelay at Torque Limit.Current limitSet the current limit in parameter 4-18 Current Limit. Set thetime before the current limit warning trips inparameter 14-24 Trip Delay at Current Limit.Minimum speed limitParameter 4-11 Motor Speed Low Limit [RPM] orparameter 4-12 Motor Speed Low Limit [Hz] limit theoperating speed range to for instance between 30 and50/60 Hz. Maximum speed limit: Parameter 4-13 MotorSpeed High Limit [RPM] or parameter 4-19 Max OutputFrequency limit the maximum output speed the frequencyconverter can provide.ETR (electronic thermal relay)The ETR function measures actual current, speed, and timeto calculate motor temperature and protect the motorfrom being overheated (warning or trip). An externalthermistor input is also available. ETR is an electronicfeature that simulates a bimetal relay based on internalmeasurements. The characteristic is shown inIllustration 3.12.System Integration VLT® Decentral Drive FCD 30262 Danfoss A/S © 05/2018 All rights reserved. MG04H30233