Chapter 5 - Earth Fault Protection; System-Earthed Network - ABB ACS 600 User Manual

Chapter 5 – Earth Fault Protection
In Case of an Earth Fault
Further Information
System-earthed
Network
Diagram
Description
In Case of an Earth Fault
5-2
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.
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 about the insulation monitoring device is available
in IRDH265 Operating Manual (code TGH1249) published by the
manufacturer, BENDER companies.
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.
This diagram shows earth fault protection implemented with internal
current transducers in the ACA 635.
L1 L2 L3
Transformer
The line current unbalance is calculated from measured currents I
and I .
w
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.
IGBT Supply Unit
DC Busbar
~
=
I > 0, Leakage Current
L
ACA 635 IGBT Supply Sections
Inverter Units
=
=
~ ~
M
M
3~
3~
, I
U V