ABB ACS800 Series Hardware Manual page 87

The monitoring device is connected between the ungrounded system and the drive
grounding conductor (PE). The IRDH275 monitors the insulation resistance of the IT
system.
L1 L2 L3
Transformer
A pulsating AC measuring voltage is superimposed on the system (measuring
principle Adaptive Measuring Pulse, developed by BENDER). The measuring pulse
consists of positive and negative pulses of the same amplitude. The period depends
on the respective leakage capacitances and the insulation resistance of the system
to be monitored.
The response values and other function parameters of the IRDH275 are set via the
function keys. The parameters are indicated on the display and stored in a non-
volatile memory after the setting is completed. It is possible to set two response
values, Alarm 1 (prewarning) and Alarm 2 (main alarm), in the range of 1 kohm to
10 Mohm. Both response values have their own alarm LEDs and relays. If the
reading is below the set response value, the associated alarm relay responds, the
alarm LED lights up and the measuring value is indicated on the display. The
function of the alarm relay depends on its setting.
When auxiliary power to the IRDH275 is switched off, the alarm relay is switched to
the fault position.
In case of an earth fault, the indicator light illuminates on the door of the drive
cabinet.
Supply unit
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BENDER
insulation
monitoring device
Fault current
Earth fault monitoring in IT (ungrounded) systems (+Q954)
Inverter units
DC busbar
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=
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M
M
3~
3~
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