See EN/IEC61800-5-1 and EN 50178 for further information.
Using RCDs
Where residual current devices (RCDs), also known as
ground leakage circuit breakers, are used, comply with the
following:
•
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 congu-
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
Figure 10.14 Main Contributions to Leakage Current
The amount of leakage current detected by the RCD
depends on the cut-o frequency of the RCD.
130BB957.11
Leakage current [mA]
100 Hz
2 kHz
100 kHz
Figure 10.15 Inuence of the RCD Cut-o Frequency on
Leakage Current
10.10
IT Mains
Mains supply isolated from ground
If the drive is supplied from an isolated mains source (IT
mains, oating delta, or grounded delta) or TT/TN-S mains
with grounded leg, the RFI switch is recommended to be
turned o via parameter 14-50 RFI 1 on the drive and
parameter 14-50 RFI 1 on the lter. For more detail, see IEC
364-3. In the o position, the lter capacitors between the
chassis and the DC link are cut o to avoid damage to the
DC link and to reduce the ground capacity currents,
according to IEC 61800-3.
If optimum EMC performance is needed, or parallel motors
are connected, or the motor cable length is above 25 m
(82 ft), Danfoss recommends setting parameter 14-50 RFI 1
to [ON]. Refer also to the Application Note, VLT on IT Mains.
It is important to use isolation monitors that are rated for
use together with power electronics (IEC 61557-8).
Danfoss does not recommend using an output contactor
for 525–690 V drives connected to an IT mains network.
Electrical Installation Con... Design Guide
MG22B222 Danfoss A/S © 01/2018 All rights reserved. 171
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