Device description
13
isoGEN523_D00320_04_M_XXEN/06.2018
3.2.3
General measuring functions
The ISOMETER® measures the RMS value of the nominal system voltage
U
n
between L1/
+ and L2/- as well as the residual voltages
U
L1e
(between L1/+ and earth) and
U
L2e
(between L2/- and earth).
When coupled to a
DC system
, the ISOMETER® determines from a minimum value of
the nominal system voltage the fault y conductor L1/+ or L2/- which shows the distri-
bution of the insulation resistance between conductors L1/+ and L2/-. The distribution
is indicated by a "+" or "-" sign preceding the insulation resistance measurement. The
value range of the fault y conductor is ±100 %:
The partial resistances can be calculated from the total insulation resistance
R
F
and the
fault y conductor (R %) using the following formula:
Fault on conductor L1/+ ->
R
L1F
= (200 % *
R
F
)/(100 % + R %)
Fault on conductor L2/- ->
R
L2F
= (200 % *
R
F
)/(100 % – R %)
When the ISOMETER® is coupled to an
AC system
, the fault y conductor can only be de-
termined in a connected DC system and the fault is detected either on L1/+ (+100 %) or
L2/- (-100 %). Calculating the fault distribution is not possible in this case.
If the values
R
F
or
U
n
reach or violate the activated response values for the period
t
on
without interruption, an alarm is signalled via the relays "K1" and "K2". If the values
R
F
or
U
n
do not reach or violate their release value (response value plus hysteresis)
for the pe-
riod
t
off
without interruption, the alarm relays will switch back to their initial position. If
the fault memory is enabled, the alarm relays remain in the alarm state until the external
test/reset button is pressed or until the supply voltage is switched off.
The device function can be tested using the external T/R button. Parameterisation of
the ISOMETER® is possible via the BMS bus, for example by means of a BMS-Ethernet
gateway (COM465IP) or Modbus RTU.
3.2.4
Isolation from the system to be monitored
If the device has no supply voltage or is in stop mode (see
), it decouples termi-
nals L1/+ and L2/- internally from the IT system being monitored. In this case, an insu-
lation measurement up to DC 500 V can be carried out using an insulation tester.
Indication
Meaning
-100 %
One-sided fault on conductor L2/-
0 %
Symmetrical fault
+100 %
One-sided fault on conductor L1/+
