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

2.9 General Aspects of EMC2.9.1 General Aspects of EMC EmissionsElectrical interference is most commonly conducted at frequencies in the range 150 kHz to 30 MHz. Airborne interferencefrom the frequency converter system in the range 30 MHz to 1 GHz is generated from the inverter, motor cable, and themotor.As shown in Illustration 2.18, capacitive currents in the motor cable coupled with a high dU/dt from the motor voltagegenerate leakage currents.The use of a screened motor cable increases the leakage current (see Illustration 2.18) because screened cables have highercapacitance to earth than unscreened cables. If the leakage current is not filtered, it causes greater interference on themains in the radio frequency range below 5 MHz. Since the leakage current (I1) is carried back to the unit through thescreen (I 3), in principle, there is only a small electromagnetic field (I4) from the screened motor cable according toIllustration 2.18.The screen reduces the radiated interference but increases the low-frequency interference on the mains. The motor cablescreen must be connected to the frequency converter enclosure as well as the motor enclosure. The best way to connectthem is by using integrated screen clamps to avoid twisted screen ends (pigtails). These increase the screen impedance athigher frequencies, which reduces the screen effect and increases the leakage current (I4).If a screened cable is used for fieldbus, relay, control cable, signal interface, and brake, the screen must be mounted on theenclosure at both ends. In some situations, however, it is necessary to break the screen to avoid current loops.Earth PlaneLINE FREQUENCY MOTOR CABLE SCREENED MOTORCONVERTEREarth wireScreenzzzL1L2L3PEUVWPE175ZA062.11C SI 2I 1I 3I 4C S C S C SC SI 4C Sz PEIllustration 2.18 Leakage CurrentsIllustration 2.18 shows an example of a 6-pulse frequency converter, but could be applicable to a 12-pulse as well.If placing the screen on a mounting plate for the frequency converter, the mounting plate must be made of metal, becausethe screen currents must be conveyed back to the unit. Ensure good electrical contact from the mounting plate through themounting screws to the frequency converter chassis.When unscreened cables are used, some emission requirements are not complied with, although the immunityrequirements are observed.To reduce the interference level from the entire system (unit and installation), make motor and brake cables as short aspossible. Avoid placing cables with a sensitive signal level alongside motor and brake cables. Radio interference higher than50 MHz (airborne) comes from the control electronics. See 5.10 EMC-correct Installation for more information on EMC.Introduction VLT® AQUA Drive FC 202 Design Guide30 MG20Z102 - VLT® is a registered Danfoss trademark22