Chapter 2 – Twelve–Pulse Technology
II F2
2 - 8 DCS 600 Manual for 12 – Pulse Operation
2.4 Earth fault (insulation) monitoring
Monitoring of first
earth fault
The following details have to be taken into consideration for earth
fault (insulation) monitoring in 12 – pulse configurations:
This earth fault monitoring is used for insulated (IT) networks and
12 – pulse/ sequential configurations The insulation monitor super-
vises continuously the AC terminals
(L
1
, L
2
, L
3
) or the DC terminals
(L
+
, L
-
).
The converter can handle a floating of the neutral voltage point up to
the level of an earthed line phase. With higher floating voltage levels
the converter will trip signalling Synchronization Fault
(F 31). The line
is grounded by the internal high-ohmic measuring resistor Rm of the
insulation monitor.
The application principles of such an insulation monitor unit are ex-
plained with an example manufactured by the company BENDER.
Insulation moni-
tor unit “ISO-
METER“ type
IRDH 265 – 3
(Bender-Relay)
The insulation monitor unit “ISOMETER“ type IRDH 265 – 3 manu-
factured by BENDER can handle up to 440V AC between the inputs
with Ri = 60kΩ and up to 220V AC or DC between the inputs with
Ri = 40kΩ:
KE
L1
60k
(L/+)
40k
L2
60k
(L/-)
40k
L3
60k
AK
34k
Figure 2/9
If the base unit type IRDH 265 - 3 is used for higher voltages a sup-
plementary unit of the type AGH xxx will be required according to the
BENDER documentation.
The result of the combination of a base unit and of a supplementary
unit is that the Rm values are higher than 60kΩ + 34kΩ = 94kΩ or
than 40kΩ + 34kΩ = 74kΩ. However, a supplementary unit is not
shown in the following figures in order to keep them clear. The figures
shall clarify the principles only, not the detailed solutions.
The 34kΩ base resistance includes the 4.2 kΩ winding resistance
of a high inductive choke. Therefore the base AC impedance is
higher than 34kΩ.
Insulated DC
drive, 12 – pulse
parallel configu-
ration
Figure 2/10 is the synopsis of an insulated DC drive with two thyristor
power converters in a 12 – pulse parallel configuration, with an inter-
phase transformer (T-reactor), with a dedicated power transformer and
with one insulation monitor unit type IRDH from BENDER.
INSULATION
MONITOR
IRDH
Rm
Rm
(L/+)
(L/-)
KE
0
Figure 2/10
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