ABB ACS 600 MultiDrive, User Manual

Page: 33 / 109

Chapter 5 – Earth Fault Protection
5-2 ACA 635 IGBT Supply Sections
With Bender’s insulation monitoring device it’s possible to set up two
response values: ALARM1 and ALARM2. Both values have an own
alarm LED, which illuminates if reading is below these selected
response values.
In Case of an Earth Fault An earth fault closes the measuring circuit. An electronic evaluation
circuit calculates the insulation resistance which is indicated on an LC
display or an external ohmmeter after the response time.
The alarm actions depend on the electric connection: for example
ALARM1 may only give a warning and ALARM2 may trip the device.
Further Information Further information about the insulation monitoring device is available
in
IRDH265 Operating Manual (code TGH1249) published by the
manufacturer, BENDER companies.
System-earthed
Network
In a system-earthed network, the neutral point of the supply
transformer is earthed solidly. This section describes an internal earth
fault protection principle in a system-earthed network.
Diagram This diagram shows earth fault protection implemented with internal
current transducers in the ACA 635.
Description The line current unbalance is calculated from measured currents I
U
, I
V
and I
w
.
In Case of an Earth Fault In normal operation the current sum is zero. An earth fault leads to an
unbalance in the 3-phase system and therefore to a current sum
different from zero. If the current unbalance exceeds the limit set in
Par. 30.03 EARTH FAULT LEVEL, an alarm is given or the device is
tripped.
~
=
~
=
L1 L2 L3
~
=
M
3~
M
3~
I
L
> 0, Leakage Current
Transformer
IGBT Supply Unit
DC Busbar
Inverter Units