ABB CM-Serie Betriebs- Und Montageanleitung Seite 11

V Function diagrams
a) Insulation resistance monitoring without fault storage,
auto reset
b) Insulation resistance monitoring with fault storage,
manual reset
Control supply voltage
Remote Test
Remote Reset
Measured value
Hysteresis
Threshold value
Closed-circuit principle
Output relay
Green LED
Red LED
Yellow LED
Monitoring functions
The CM-IWS.1 serves to monitor insulation resistance in accor-
dance with IEC 61557-8 in unearthed IT AC systems, IT AC sys-
tems with galvanically connected DC circuits, or unearthed IT DC
systems.
The CM-IWS.2 is used to monitor insulation resistance in accor-
dance with IEC 61557-8 in unearthed, pure IT AC systems.
The insulation resistance between system lines and system earth
is measured. If this falls below the adjustable threshold value, the
output relay de-energizes.
Measured input voltage for
CM-IWS.2: 0-400 V AC, 45-65 Hz
CM-IWS.1: 0-300 V DC or 0-250 V AC, 15-400 Hz
The devices can monitor control circuits (single-phase) and main
circuits (3-phase).
Measuring principle
With CM-IWS.1 a pulsating measuring signal is fed into the system
to be monitored and the insulation resistance calculated. This pul-
sating measuring signal alters its form depending on the insulation
resistance and the system leakage capacitance. From this altered
form the change in the insulation resistance is forecast. When the
forecast insulation resistance corresponds to the insulation resis-
tance calculated in the next measurement cycle and is smaller than
the set threshold value, the output relay de-energizes. This mea-
suring principle is also suitable for the detection of symmetrical
insulation faults.
With CM-IWS.2 a superimposed DC measuring signal is used for
measurement. From the superimposed DC measuring voltage and
its resultant current the value of the insulation resistance of the
system to be monitored is calculated.
Additional monitoring functions CM-IWS.1
The CM-IWS.1 cyclicly monitors the measuring circuit connections
w
and KE for wire interruption. In case of a wire interruption in one
of the connections, the output relay de-energizes.
In addition, the unearthed AC-, DC- or AC/DC system is monitored
for inadmissible system leakage capacitance. If the system leakage
capacitance is too high, the output relay de-energizes.
English
Operating mode
The system to be monitored is connected to terminals L (CM-
IWS.2) or L+, L- (CM-IWS.1). The earth potential is connected to
w
terminals and KE.
The devices operate according to the closed-circuit principle – fault
state: relay de-energized.
Once the control supply voltage has been applied the insulation
monitoring relay runs through a system test routine. The system
is diagnosed and the settings are tested. If no internal or external
faults are found after this test routine is completed, the output
relay energizes.
If the measured value drops below the set threshold value, the out-
put relay de-energizes. If the measured value exceeds the thresh-
old value plus hysteresis, the output relay re-energizes.
All operating states are signalled by the front-face LEDs.
See table „LEDs, status information and fault messages"
Test function
is only possible when there is no fault.
By pressing the front-face combined test/reset button a system
test routine is executed. The output relay remains de-energized,
as long as the test button is pressed, the control contact S1-S3 is
closed or the test functions are processed.
Fault storage, reset function
The output relay remains de-energized and only energizes after the
combined test/reset button is pressed or after the remote reset
(terminals S2-S3) is activated, and when the insulation resistance
is higher than the set threshold value plus hysteresis.
11