Danfoss VLT HVAC Basic Drive FC 100 Series Design Manual

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Danfoss VLT HVAC Basic Drive FC 100 Series Design Manual Manual pdf 36 page image

NOTELeakage CurrentThe earth leakage current from the frequency converterexceeds 3.5mA. To ensure that the earth cable has a goodmechanical connection to the earth connection, the cablecross section must be at least 10mm2 or 2 rated earthwires terminated separately.Residual Current DeviceThis product can cause a DC current in the protectiveconductor. Where a residual current device (RCD) is usedfor protection in case of direct or indirect contact, only anRCD of Type B is allowed on the supply side of thisproduct. Otherwise, another protective measure shall beapplied, such as separation from the environment bydouble or reinforced insulation, or isolation from thesupply system by a transformer. See also Application NoteProtection against Electrical Hazards MN.90.G2.02.Protective earthing of the frequency converter and the useof RCDs must always follow national and local regulations.2.10 Extreme Running ConditionsShort Circuit (Motor Phase – Phase)The frequency converter is protected against short circuitsby means of current measurement in each of the threemotor phases or in the DC link. A short circuit betweentwo output phases will cause an overcurrent in theinverter. The inverter will be turned off individually whenthe short circuit current exceeds the permitted value(Alarm 16 Trip Lock).To protect the frequency converter against a short circuitat the load sharing and brake outputs please see thedesign guidelines.See certificate in the Certificates section.Switching on the OutputSwitching on the output between the motor and thefrequency converter is fully permitted. The frequencyconverter will not be damaged in any way by switching onthe output. However, fault messages may appear.Motor-generated Over-voltageThe voltage in the intermediate circuit is increased whenthe motor acts as a generator. This occurs in followingcases:1. The load drives the motor (at constant outputfrequency from the frequency converter), ie. theload generates energy.2. During deceleration ("ramp-down") if the momentof inertia 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.3. Incorrect slip compensation setting (1-62 SlipCompensation) may cause higher DC link voltage.The control unit may attempt to correct the ramp ifpossible (2-17 Over-voltage Control.)The inverter turns off to protect the transistors and theintermediate circuit capacitors when a certain voltage levelis reached.Mains Drop-outDuring a mains drop-out, the frequency converter keepsrunning until the intermediate circuit voltage drops belowthe minimum stop level, which is typically 15% below thefrequency converter's lowest rated supply voltage. Themains voltage before the drop-out and the motor loaddetermines how long it takes for the inverter to coast.2.10.1 Motor Thermal ProtectionThis is the way Danfoss protects the motor from beingoverheated. It is an electronic feature that simulates abimetal relay based on internal measurements. The charac-teristic is shown in the following figure.1.21.0 1.43010201006040501.81.6 2.020005002004003001000600t [s]175ZA052.12fOUT = 2 x f M,NfOUT = 0.2 x f M,NfOUT = 1 x f M,N (par. 1-23)I M,N(par. 1-24)I MThe X-axis is showing the ratio between Imotor and Imotornominal. The Y-axis is showing the time in seconds beforethe ETR cuts off and trips the drive. The curves areshowing the characteristic nominal speed at twice thenominal speed and at 0.2x the nominal speed.It is clear that at lower speed the ETR cuts of at lower heatdue to less cooling of the motor. In that way the motorare protected from being over heated even at low speed.The ETR feature is calculating the motor temperaturebased on actual current and speed.The thermistor cut-out value is > 3kΩ.Integrate a thermistor (PTC sensor) in the motor forwinding protection.Introduction to VLT HVAC Ba... VLT HVAC Basic Drive Design GuideMG.18.C2.02 - VLT® is a registered Danfoss trademark 352 2