Danfoss VLT AutomationDrive FC 301, Руководство по конструкции, Страница: 137 / 200

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.
130BB955.12
a
b
Leakage current
Motor cable length
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.
130BB956.12
THVD=0%
THVD=5%
Leakage current
Illustration 9.38 Line Distortion Influences Leakage Current
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:
•
Ground wire (terminal 95) of at least 10 mm
2
•
2 separate ground wires both complying with the
dimensioning rules
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:
•
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
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.
130BB958.12
f
sw
Cable
150 Hz
3rd harmonics
50 Hz
Mains
RCD with low f
cut-
RCD with high f
cut-
Leakage current
Frequency
Illustration 9.39 Main Contributions to Leakage Current
Electrical Installation
VLT
®
AutomationDrive FC 301/FC 302 Design Guide, 0.25-75 kW
MG33BF02 - Rev. 2013-12-20 135
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