Leakage Current; Ground Leakage Current - Danfoss VLT DriveMotor FCP 106 Design Manual

Product Overview

2.7 Leakage Current

2.7.1 Ground Leakage Current

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Follow national and local codes regarding protective
earthing of equipment where leakage current exceeds 3.5
mA.
Frequency converter technology implies high frequency
switching at high power. This generates a leakage current
in the ground connection.
The ground leakage current is made up of several contri-
butions and depends on various system configurations,
including:
•
RFI filtering.
•
Motor cable length.
•
Motor cable screening.
•
Frequency converter power.
Leakage current
Illustration 2.21 Motor cable length and power size influence
on leakage current. Power size a > power size b
The leakage current also depends on the line distortion.
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VLT DriveMotor FCP 106/FCM 106
Leakage current
Illustration 2.22 Line Distortion Influences Leakage Current
a
If the leakage current exceeds 3.5 mA, compliance with
EN/IEC61800-5-1 (power drive system product standard)
requires special care.
Reinforce grounding with the following protective ground
connection requirements:
•
b
•
Motor cable length
See EN/IEC61800-5-1 and EN 50178 for further information.
Using RCDs
Where residual current devices (RCDs), also known as earth
leakage circuit breakers (ELCBs), are used, comply with the
following:
•
•
•
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.
Danfoss A/S © 06/2016 All rights reserved.
Ground wire (terminal 95) of at least 10 mm
cross-section.
2 separate ground wires both complying with the
dimensioning rules.
Use RCDs of type B only as they can detect AC
and DC currents.
Use RCDs with a delay to prevent faults due to
transient ground currents.
Dimension RCDs according to the system configu-
ration and environmental considerations.
THDv=0%
THDv=5%
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MG03M202