30 Digitax ST Installation Guide
Issue: 7
4.5 Ground leakage
The ground leakage current depends upon whether the internal EMC filter is installed.
The drive is supplied with the filter installed. Instructions for removing the internal filter
are given in Figure 4-3.
With the internal EMC filter fitted the ground leakage current is as follows:
Table 4-3 Ground leakage current with internal EMC filter installed
With internal EMC filter removed the ground leakage current = <1 mA.
4.5.1 Use of residual current device (RCD)
There are three common types of ELCB / RCD:
1. AC - detects AC fault currents
2. A - detects AC and pulsating DC fault currents (provided the DC current reaches
zero at least once every half cycle)
3. B - detects AC, pulsating DC and smooth DC fault currents
• Type AC should never be used with drives
• Type A can only be used with single phase drives
• Type B must be used with three phase drives
If an external EMC filter is used, a delay of at least 50 ms should be incorporated to
ensure spurious trips are not seen. The leakage current is likely to exceed the trip level
if all of the phases are not energized simultaneously.
4.6 EMC
4.6.1 Internal EMC filter
It is recommended that the internal EMC filter is kept in place unless there is a specific
reason for removing it.
Special attention is required when using a DST120X model on an ungrounded supply
(IT supply). In the event of a ground fault in the motor circuit the drive may not trip and
the filter could be overstressed. In this case, either the filter must be removed or
additional independent motor ground fault protection must be provided.
The internal EMC filter reduces radio-frequency emissions into the mains supply. Where
the motor cable is short, it permits the requirements of EN 61800-3:2004 to be met for
Model
3 phase Star
ground
3 phase Delta
ground
1 phase
mA
DST120X at 220V 4 10 3
DST140X at 400V 12 40
The above leakage current is just the leakage current of the drive with the internal EMC filter
connected and does not take into account any leakage currents of the motor or motor cable.
In both cases, there is an internal voltage surge suppression device connected to
ground. Under normal circumstances, this carries negligible current.
When the internal EMC filter is installed, the leakage current is high. In this case, a
permanent fixed ground connection must be provided with a cross sectional area equal
to 10 mm
2
.
Only type B ELCB / RCD are suitable for use with 3 phase inverter drives.
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