Accessories
127
3ADW000462R0301 DCS880 Hardware Manual e c
Control unit
The control unit includes the following main blocks:
– Micro controller H8 for control and firing.
– Actual DC current measurement using an AC current transformer.
– High ohmic measurement of AC and DC voltage.
Residual resistance to ground =3.5 M(DCF803
=1.9 M(DCF804)
– RS485 interface and DCSLink interface to the converter's controller board SDCS-CON-H01.
– The firmware of the field exciter is stored in a flash memory and contains:
– The PI current controller for the field circuit.
– The fault and reset logic.
– The synchronization and PLL function.
– The bridge reversal function (only DCF804-0050 / 0060).
All control parameters are set from armature converter via drive-to-drive communication. The field
current reference, actual field current, current control and status bit are cyclic sent via drive-to-drive
communication.
The field exciter is equipped with an autoscaling function of the burden resistors based on the
nominal field current of the motor.
Power part
The DCF803-0050 / 0060 is a half-controlled single-phase bridge. A half controlled bridge does not
need a free wheeling circuit.
The DCF804-0050 / 0060 is a full-controlled single-phase bridge. During normal operation it is fired in
half controlled mode to reduce the current ripple.
Full controlled bridges require separate freewheeling circuits. The firing control enables the
freewheeling of a thyristor if the DC voltage increases. See also parameters 28.62 and 42.67 in the
armature converter.
A MOV (Metal Oxide Varistor) protects the AC input against voltage spikes from the mains.
Another MOV protects the DC output against voltage surges which can be caused by the field
winding of a DC machine.
The power section is equipped with a line reactor (L1). Thus an external line reactor is not needed.
Single-phase field exciters are typically supplied by autotransformers if the rated field voltage is less
than 60 % of the AC supply voltage.
The AC input current can be estimated like this:
I
AC
= 1.1* I
DC
* U
DC
field / U
AC
supply.
R902
R903
SDCS-FEX-81 DCF804-0050 / 0060
SDCS-FEX-82 DCF803-0050 / 0060
50 A
60 A
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