Functional Description; Monitoring The Insulation Resistance - Bender ISOMETER isoES425 Manual

2.3

Functional description

The ISOMETER® measures the insulation resistance R
system to be monitored (L1/+, L2/–) and earth (PE). The RMS value of the system voltage U
L2/– as well as the residual voltages U
measured.
From a minimum system voltage in the DC system, the ISOMETER® determines the faulty conductor "R %",
which shows the distribution of the insulation resistance between conductors L1/+ and L2/–. The distribution
is indicated by a positive or negative sign preceding the insulation resistance measurement. The value range of
the faulty conductor is ±100 %:
Indication Meaning
–100 % one-sided fault at conductor L2/–
0 % symmetrical fault
+100 % one-sided fault at conductor L1/+
The partial resistances can be calculated from the total insulation resistance R
using the following formula:
• Fault at conductor L1/+: R
• Fault at conductor L2/–: R
In the AC system, the location of the fault in the DC link is indicated by a positive or negative sign preceding
the insulation resistance measured value in the AC system from a minimum nominal system voltage between
the AC system and earth, caused by a fault in a connected DC circuit. A percentage distribution to the location
of the fault is not possible. The faulty conductor "R %" is only represented as a one-sided fault on L1/+ (+100 %)
or L2/– (–100 %).
Also from a minimum voltage, the ISOMETER® determines the insulation resistance R
voltages U and U
L1e L2e
indicator in cases where the ISOMETER® has to adapt to an R
The detected fault is assignable to an alarm relay via the menu. If the values R
values activated in the "AL" menu, this will be indicated by the LEDs and relays "K1" and "K2" according to the
signalling assignment set in the "out" menu. In addition, the menu offers the setting of the relay operation and
the activation of the fault memory "M".
If the values R or U do not violate their release value (response value plus hysteresis) for the period t
F n
without interruption, the alarm relays will switch back to their initial position and the alarm LEDs stop lighting.
If the fault memory is activated, the alarm relays remain in alarm position and the LEDs are lit until the reset key
"R" is pressed or the supply voltage U
The device function can be checked with the test button "T".
Parameters are assigned to the device via the LCD and the control buttons on the front panel; this function
can be password-protected. Parameterisation is also possible via the BMS bus, for example by using the BMS
Ethernet gateway (COM465IP) or the Modbus RTU.
2.3.1

Monitoring the insulation resistance

The insulation resistance R
chapter 4.4.3). The value "R1" can only be set higher than the value "R2". If the insulation resistance R
or falls below the activated values "R1" or "R2", an alarm message is triggered. If R
"R2" plus the hysteresis value, the alarm will be cleared.
(between L1/+ and earth) and U
L1e
= (200 % × R
L1F
= (200 % × R
L2F
. It is an approximate value for one-sided insulation faults and can be used as a trend
is interrupted.
s
is monitored by means of the parameters "R1" (prewarning) and "R2" (alarm) (see
F
and the system leakage capacitance C
F
) / (100 % + R %)
F
) / (100 % – R %)
F
and C
F
isoES425_D00214_01_M_XXEN/10.2023
(between L2/– and earth) are also
L2e
and the faulty conductor "R %"
F
from the residual
UGe
relation that varies considerably.
e
or U violate the response
F n
exceeds the values "R1" or
F
ISOMETER® isoES425
between the
e
between L1/+ and
n
off
reaches
F
9