Danfoss VLT AutomationDrive FC 301 Design Manual page 137

Electrical Installation
The earth leakage current is made up of several contri-
butions and depends on various system configurations
including RFI filtering, motor cable length, motor cable
screening, and frequency converter power.
Leakage current
Illustration 9.37 Motor Cable Length and Power Size Influence
on Leakage Current. Powersize a > Powersize b
The leakage current also depends on the line distortion.
Leakage current
Illustration 9.38 Line Distortion Influences Leakage Current
®
VLT AutomationDrive FC 301/FC 302 Design Guide, 0.25-75 kW
EN/IEC61800-5-1 (Power Drive System Product Standard)
requires special care if the leakage current exceeds 3.5 mA.
Grounding must be reinforced in one of the following
ways:
•
•
a
See EN/IEC61800-5-1 and EN50178 for further information.
Using RCDs
Where residual current devices (RCDs), also known as earth
leakage circuit breakers (ELCBs), are used, comply with the
following:
•
b
•
Motor cable length
•
The leakage current includes several frequencies
originating from both the mains frequency and the
switching frequency. Whether the switching frequency is
detected depends on the type of RCD used.
Leakage current
THVD=0%
THVD=5%
Illustration 9.39 Main Contributions to Leakage Current
MG33BF02 - Rev. 2013-12-20
Ground wire (terminal 95) of at least 10 mm
2 separate ground wires both complying with the
dimensioning rules
Use RCDs of type B only as they are capable of
detecting AC and DC currents
Use RCDs with a delay to prevent faults due to
transient earth currents
Dimension RCDs according to the system configu-
ration and environmental considerations
RCD with low f
cut-
RCD with high f
50 Hz 150 Hz
Mains 3rd harmonics
2
cut-
Frequency
f
sw
Cable
135
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