ABB DCS 500B, Description

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Functional Software description
DCS 500 Software Description 51
Internal Field Exciter
SDCS-FEX-2 Internal field exciter FEX2 is a half controlled bridge that can control
the field current in one (positive) direction. Because of the nature of
the half controlled bridge, a very small amount of current (5...10%)
flows always through the bridge if the field contactor is closed.
SDCS-FEX-2 is controlled via a serial communication link. FEX2
measures the field current and sends the value to the drive via se-
rial communication.
Acknowledge The measured field current is used to form an acknowledge signal.
If the field current exceeds the overcurrent limit, the drive will trip to
the fault FIELD EX 1 OVERCURR. A low level of field current
blocks the controllers immediately, but the low level must be active
at least 6 seconds before the drive will trip to the fault: NO FIELD
ACK.
External Field Exciter
DCF503-0050 For the control point of view the DCF503-0050 is similar to SDCS-
FEX-2. The differences are that DCF503-0050 can handle a higher
field current than SDCS-FEX-2, and its mechanical size is larger.
The control board type is SDCS-FEX-32.
External Field Exciter
DCF504-0050 External field exciter DCF504-0050 can control the field current ei-
ther to the positive or negative direction. The direction is selected
by the sign of the field current reference. A positive sign means
"forward" bridge and negative sign "reverse" bridge.
The field current supervision logic is handled in the same way as in
SDCS-FEX-2. The control board type is SDCS-FEX-31.
AI/DI Connected
Field Exciters When modifying existing machines ("revamping") the old field ex-
citers are often reused. In this case an acknowledge signal must be
formed in order to supervise the field function. This can be done
using either digital or analog input.
When a digital input is used to form the acknowledge signal, the
function is similar to that used with FEX1, the diode field exciter.
Acknowledge
Selection The acknowledge signal is selected with the same parameter that
is used for selecting the field exciter type. Acknowledge signal is
connected to input
[F1 ACK] (1304)
FEXC SEL (505)
...
5 = [FIELD ACK VIA DI]
field acknowledge through DI
6 = [FIELD ACK VIA AI]
field acknowledge through AI