Functional Software description
DCS 500 Software Description 59
Saturation The motor starts to saturate after a certain field current, and thus
the relation of field current and motor flux is not linear. For this rea-
son the field current cannot be directly used to define FLUX inside
the motor. On the other hand, the motor armature voltage without
load (= EMF) is directly proportional to the motor flux and motor
speed below the field weakening area.
For example, if the motor nominal DC voltage is 440V, and we are
running the motor at half speed and full FLUX, then the DC voltage
is about 220V. Then, if we reduce the flux to 50% and keep the
same speed, the DC voltage is about 110V. (This is only an exam-
ple!)
Because the motor EMF-voltage is directly proportional to motor
FLUX it is possible to define the relationship between the field cur-
rent and the motor FLUX by measuring the motor armature voltage
without load (EMF).
The main idea for linearisation is to find a field current that produces
the desired EMF-voltage at a certain speed. Linearisation is done
with a function block that needs three defined values, field currents
for a 90%, 70% and 40% flux. The other values are interpolated.
During the commissioning the values must be defined for the func-
tion block if the EMF-controller is to be used. Only the EMF-
controller uses the linearisation function.
Linearisation
procedure see OPERATING INSTRUCTION
Field reduction
when at stand-
still
The motor field can be reduced during standstill in order to avoid
overheating when the motor is not running. The function can be ac-
tivated by means of two parameters:
F1 RED SEL (1313) Selection for the first motor
F2 RED SEL (1510) Selection for the second motor in the case of
shared motion.
The used current reference can be selected by means of two pa-
rameters:
F1 RED REF (1314) Reference for the first motor
F2 RED REF (1511) Reference for the second motor in the
case of shared motion.
The function is activated when
- "ON"-command is "1", ie., the main contactor is closed
- the drive is in RDY RUN state.
- 10 seconds has elapsed.
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