Danfoss VLT 5000 Series Design Manual
Also see for VLT 5000 Series: ManualInstruction manualInstructionsOperating instructionsQuick setup
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Extreme Running ConditionsShort circuitThe frequency converter is protected against short cir-cuits by means of current measurement in each of thethree motor phases. A short circuit between two outputphases will cause an overcurrent in the inverter. How-ever, each transistor of the inverter will be turned offindividually when the short circuit current exceeds thepermitted value.After 5-10 s the driver card turns off the inverter andthe frequency converter will display a fault code, al-though depending on impedance and motor frequen-cy.Earth faultThe inverter cuts out within a few s in case of an earthfault on a motor phase, although depending on impe-dance and motor frequency.Switching on the outputSwitching on the output between the motor and thefrequency converter is fully permitted. It is not possibleto damage VLT 5000 Series in any way by switchingon the output. However, fault messages may appear.Motor-generated overvoltageThe voltage in the intermediate circuit is increasedwhen the motor acts as a generator. This occurs in twocases:1. The load drives the motor (at constant outputfrequency from the frequency converter), ie.the load generates energy.2. During deceleration ("ramp-down") if the mo-ment of inertia is high, the load is low and theramp-down time is too short for the energy tobe dissipated as a loss in the requency con-verter, the motor and the installation.The control unit attempts to correct the ramp if possi-ble.The inverter turns off to protect the transistors and theintermediate circuit capacitors when a certain voltagelevel is reached.Mains drop-outDuring a mains drop-out, the frequency converter con-tinues until the intermediate circuit voltage drops be-low the minimum stop level, which is typically 15%below the frequency converter's lowest rated supplyvoltage.The time before the inverter stops depends on themains voltage before the drop-out and on the motorload.Static overloadWhen the frequency converter is overloaded (the tor-que limit in parameter 221/222 has been reached), thecontrols will reduce the output frequency in an attemptto reduce the load.If the overload is excessive, a current may occur thatmakes the frequency converter cut out after approx.1.5 sec.Operation within the torque limit can be limited in time(0-60 s) in parameter 409.VLT ® 5000 Design GuideMG.52.B2.02 - VLT ® is a registered Danfoss trademark 111Special conditions |
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