Danfoss VLT HVAC Drive FC 100 Series Design Manual

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The ground leakage current is made up from severalcontributions and depends on various system configu-rations including RFI filtering, shielded motor cables andadjustable frequency drive power.ab 130BB955.10Cable length [m]Leakage current [mA]Figure 2.33 Cable Length and Power Size Influence on LeakageCurrent. Pa > Pb.130BB956.10Leakage current [mA]THVD=0%THVD=5%Figure 2.34 Line Distortion Influences Leakage Current.NOTE!When a filter is used, turn off 14-50 RFI Filter whencharging the filter, to avoid a high leakage current makingthe RCD switch.EN/IEC61800-5-1 (Power Drive System Product Standard)requires special care if the leakage current exceeds 3.5mA.Grounding must be reinforced in one of the followingways:• Ground wire (terminal 95) of at least 0.016 in2[10mm2]• Two separate ground wires both complying withthe dimensioning rulesSee EN/IEC61800-5-1 and EN50178 for further information.Using RCDsWhere residual current devices (RCDs), also known asground leakage circuit breakers (ELCBs), are used, complywith the following:Use RCDs of type B only which are capable ofdetecting AC and DC currentsUse RCDs with an inrush delay to prevent faultsdue to transient ground currentsDimension RCDs according to the system configu-ration and environmental considerationsL leakage[mA]f [Hz]fswCablefs150 Hz3rd harmonics50 HzMains130BB958.10RCD with low fcut-offRCD with high fcut-offFigure 2.35 Main Contributions to Leakage Current.Leakage current [mA]100 Hz130BB957.102 kHz100 kHzFigure 2.36 The influence of the cut-off frequency of the RCD onwhat is responded to/measured.See also RCD Application Note, MN.90.GX.02.2.12 Brake Function2.12.1 Selection of Brake ResistorIn certain applications, for instance in tunnel orunderground railway station ventilation systems, it isdesirable to bring the motor to a stop more rapidly thancan be achieved through controlling via ramp-down or byfree-wheeling. In such applications, dynamic braking with abraking resistor may be utilized. Using a braking resistorensures that the energy is absorbed in the resistor and notin the Adjustable frequency drive.Introduction to VLT® HVAC D... VLT® HVAC Drive Design Guide2-40 MG11BB22 - VLT® is a registered Danfoss trademark22