Use Of The Analog Input Channel; Calculation Example; Two Field Exciters At The Same Time; Field Current Settings - ABB DCS 500B Description

Functional Software description
Use of the Ana-
log Input Channel
Calculation Ex-
ample
Two Field Exciters at
the same time
Field Current
Settings
52
Analog input is used when the field current is measured or con-
trolled. When controlling an AI-based field exciter, it is also neces-
sary to transfer the reference to the field exciter. This can be done
by means of connecting one analog output channel to the signal F1
CURR REF (11301). The scaling of the used analog output must
be arranged so that the value 4096 corresponds to the rated nomi-
nal excitation value as a voltage reference. The field current actual
signal must also be scaled so that the scaled input value is 4096
with rated field current.
For example, the field exciter nominal current is 32.5A, which cor-
responds to the 7V field current actual measurement. The con-
nected analog input channel is AI3.
Set:
CONV MODE (110)
HIGH VALUE (111)
LOW VALUE (112)
I MOT1 FIELDN A (503)
For more information on how to scale the AI/AO, see paragraph
Digital and Analog I/O.
When the same converter controls two motors as a "shared mo-
tion", the armature unit is switched between two motors by means
of an extra contactor. Both motors have still their own field exciters.
In the documents the main motor field exciter is called the "first
field exciter" and that of the second motor the "second field ex-
citer".
Only the "first field exciter" can be current controlled and gets it´s
current reference from the EMF CONTROL function block. The
"second field exciter" always uses either a fixed field current level
or a variable one, generated by an analog input or a similar func-
tion.
Motor standstill heating function can be used on the not-used motor
by giving a small field current reference to the field exciter.
The nominal field current must be given to the program in order to
have a correctly controlled field. Usually there is no need to change
maximum and minimum levels.
The nominal current of field exciters are set with parameters
I MOT1 FIELDN A (503)
I MOT2 FIELDN A (504)
= 1
4096*10V/7V = 5851
-4096*10V/7V = -5851
= 3250
100 = 1 A
100 = 1 A
DCS 500 Software Description