Danfoss VLT 380-500 V Design Manual

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Danfoss VLT 380-500 V Design Manual Manual pdf 115 page image

between Imotor and Imotor nominal. The Y-AXIS- shows thetime in seconds before the ETR cuts off and trips thefrequency converter. The curves show the characteristicnominal speed, at twice the nominal speed and at 0.2 xthe nominal speed.At lower speeds the ETR cuts off at lower heat due to lesscooling of the motor. In that way, the motor is protectedfrom being overheated even at low speed. The ETR featureis calculating the motor temperature based on actualcurrent and speed. The calculated temperature is visible asa readout parameter in parameter 16-18 Motor Thermal inthe frequency converter.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)IMN (par. 1-24)I MIllustration 10.11 ETR Example10.7 dU/dt ConditionsNOTICETo avoid the premature aging of motors that are notdesigned to be used with frequency converters, such asthose motors without phase insulation paper or otherinsulation reinforcement, Danfoss strongly recommends adU/dt filter or a sine-wave filter fitted on the output ofthe frequency converter. For further information aboutdU/dt and sine-wave filters see the VLT® FC-Series OutputFilters Design Guide.When a transistor in the inverter bridge switches, thevoltage across the motor increases by a dU/dt ratiodepending on:• The motor cable (type, cross-section, lengthshielded or unshielded).• Inductance.The natural induction causes an overshoot UPEAK in themotor voltage before it stabilizes itself at a leveldepending on the voltage in the DC link. The rise time andthe peak voltage UPEAK affect the service life of the motor.In particular, motors without phase coil insulation areaffected if the peak voltage is too high. Motor cable lengthaffects the rise time and peak voltage. For example, if themotor cable is short (a few meters), the rise time and peakvoltage are lower. If the motor cable is 100 m (328 ft) orlonger, the rise time and peak voltage are higher.Switching of the IGBTs causes peak voltage on the motorterminals. The frequency converter complies with thedemands of IEC 60034-25 regarding motors designed foruse with frequency converters. The frequency converteralso complies with IEC 60034-17 regarding Norm motorscontrolled by frequency converters.High-power rangeThe power sizes in Table 10.4 and Table 10.5 at theappropriate mains voltages comply with the requirementsof IEC 60034-17 regarding normal motors controlled byfrequency converters, IEC 60034-25 regarding motorsdesigned for use with frequency converters, and NEMA MG1-1998 Part 31.4.4.2 for inverter fed motors. The powersizes in Table 10.4 do not comply with NEMA MG 1-1998Part 30.2.2.8 for general-purpose motors.Filter Cablelength (m(ft))Mainsvoltage(V)Raisetime(μs)Vpeak(kV)dU/dt(kV/μs)None 150(492)400 0.818 1.06 3.249Individual 1.692 1.22 0.579Common 2.262 1.17 0.415Table 10.4 dU/dt Specifications for 380–500 V UnitsFilter Cablelength (m(ft))Mainsvoltage(V)Raisetime(μs)Vpeak(kV)dU/dt(kV/μs)None 150(492)690 0.65 1.79 2.184Individual 1.76 2.2 0.909Common 2.02 2.1 0.831Table 10.5 dU/dt Specifications for 525–690 V Units10.8 Parallel Connection of MotorsThe frequency converter can control several parallel-connected motors. When using parallel motor connection,observe the following points:• Run applications with parallel motors in U/Fmode (volts per hertz).• VVC+ mode can be used in some applications.• Total current consumption of motors must notexceed the rated output current IINV for thefrequency converter.Motor Design GuideMG37N102 Danfoss A/S © 6/2016 All rights reserved. 11310 10