Function
Function
isoBAT425_D00308_04_M_XXEN/07.2020
10
The image below shows the operating mode of the voltage comparators with the resul-
ting messages.
3.2.5 Measuring pulse period duration and operating times
In the "sEt" menu, the measuring pulse period duration
T
MP
can be configured with the
parameter "t
". The maximum operating times t
ae
(
see
of the monitoring of
R
F
and
R
C
depend on it. The modifiable measuring pulse period duration allows adjusting
the ISOMETER® to the insulation behaviour of the battery.
Measuring pulse period durations which are marked with the "auto" symbol switch au-
tomatically to the longest measuring pulse period duration as long as the message "Bat-
tery voltage
U
n
is ok" is indicated. The following table shows the maximum operating
times
t
ae
for the different alarms and measuring pulse period durations
T
MP
.
*
The value only applies to
C
e1
oder
C
e2
> 400 nF. Below this value, the absence of just one system connection is not detected.
**
The value only applies to
R
f
≤ 1,5 MΩ. Above this value, the absence of just one system connection is not reliably
detected.
T
MP
R
F
R
C
E.01
E.02
0.8 s
3.5 s
3.0 s
2.1 s
6.0 s
2.0 s
8.0 s
3.0 s
2.1 s
6.0 s
4.0 s
16 s
3.0 s
2.1 s
15 s**
8.0 s
32 s
3.0 s
2.1 s
30 s*
OverRange
Voltage fault
Hys
Battery
voltage ok
Voltage fault
Hys
Crossfault
Branch open
Hys
Connection
fault
Limit
510 V
U
BatH
U
BatL
U
CrossH
U
CrossL
0 V
-10 V
Comparator
U
nRMS
> 510 V
STAT_U_0V
U
nDC
> U
BatH
STAT_BAT_H
U
nDC
> U
BatL
STAT_BAT_L
U
nDC
> U
CrossH
STAT_CROSS_H
U
nDC
> U
CrossL
STAT_CROSS_L
U
nDC
< -10 V
E.02
Status
Message
STAT_U_0V
STAT_BAT_H
& STAT_BAT_L
! STAT_BAT_H
& STAT_CROSS_H
! STAT_BAT_L
& STAT_CROSS_L
! STAT_CROSS_H
! STAT_CROSS_L
Overvoltage
Undervoltage
Battery voltage
ok
Overvoltage
Undervoltage
Hys
Overvoltage
Undervoltage
Overvoltage
Undervoltage
3.2.6 Fault diagnosis
3.2.6.1
Insulation fault to earth
The displayed value
R
F
of the ISOMETER® is the total insulation resistance
R
F
to earth. The
polarity and the amount of residual voltages
U
L+e
and
U
L-e
are an indicator of insulation
fault location.
If the battery strings are not interconnected yet, the residual voltages
U
L+e
and
U
L-e
are
almost identical and the nominal battery voltage
U
n
is about 0 V, it is very likely that the
insulation fault is only located in one string. The polarity of the residual voltages marks
the affected string. The affected battery cell can be calculated by means of the residual
voltages
U
L+e
or
U
L-e
.
If there is an additional insulation fault in the other string, determining the cell is almost
impossible, since several variables, depending on location and size of the insulation fault,
determine the residual voltages. If the battery strings are connected to form a complete
battery, the measured value "Fault location%" indicates the fault location. Clear as-
signment is only possible in the event of a single insulation fault. The value can range bet-
ween -100 % and +100 %. The sign indicates the string affected. When the fault is located
in the middle of the battery, the fault location is 0 %.
3.2.6.2
Insulation fault between the battery strings (cross fault)
The insulation fault
R
C
(cross fault) creates a connection between the unconnected
strings and has no connection to earth. It can be detected via the
U
n
value of the voltage
measurement. If
U
n
reaches or exceeds the comparator value
U
CrossL
, the overvoltage
alarm is activated.
Depending on the fault location of the insulation fault
R
C
, an unloaded voltage on the
same level as the voltage in a battery cell up to the maximum voltage of the series con-
nection of both battery strings can occur.
R
C
directly at the coupling points is not de-
tectable due to the absence of voltage. Since the coupling impedance contains a current-
limited resistance of 10 kΩ, which is connected in parallel to the series internal resistance
of 240 kΩ of the ISOMETER®, the nominal system voltage
U
n
resulting from the insulation
fault
R
C
is loaded with this resistance. For
R
C
> 10kΩ, exceeding half the voltage of a bat-
tery cell can be considered as lower limit for the fault detection. It has to be observed that
the internal resistance of the coupling impedance is only linear up to approx. 1.5 mA and
from there, limits the current to this value. In connection with the non-linear internal re-
sistance of the coupling impedance, in case of high-resistance values of
R
C
the device er-
ror/coupling error "E.02" can occur simultaneously with the overvoltage alarm.
U
cell
=
U
Lxe
x (1 +
R
F
/
R
i
)
with ISOMETER® internal resistance
R
i
= 120 kΩ
