Free Wheeling Function; Trigger Point Setting Of The Free Feeling Function; Filter For Actual Field Current - ABB DCS 500B Description

Free Wheeling
Function
Trigger Point
Setting of the
Free Feeling
Function
Filter for Actual
Field Current
DCS 500 Software Description
The minimum field current levels are set with parameters
F1 CURR GT MIN L (1305) 4095 = rated current
F2 CURR GT MIN L (1502) 2047 = 50% of rated current
In field weakning applications minimum field current limit must be
checked. Parameter value must be below the minimum field cur-
rent.
The overcurrent level is set with parameters
F1 OVERCURR L (1306)
F2 OVERCURR L (1503)
Ext. DCF50x-0050 has a free-wheeling function to give a path for
the current if the AC-input voltage disappears for some reason, e.g.
the field contactor opens. When this happens, the current does not
stop but tends to increase the voltage of the field excitation unit
very rapidly .
The AC input voltage is measured, and if the value changes too
fast, the field excitation unit fires two selected thyristors continu-
ously open to provide a path for the current. The sensitivity for
starting the free-wheeling function can be adjusted by means of the
following parameters
F1 U AC DIFF MAX (1310)
F2 U AC DIFF MAX (1507)
Scaling is in % 1 = 1%.
The initial value is 10 % which means that the free-wheeling func-
tion starts if the two successive AC-voltage measurements in field
exciter differ more than 10 %.
The field exciter unit has a filter for smoothing the actual field cur-
rent measurement. The filter has no influence on the PI-controller
but only on the measured signal transferred to the drive software.
The filter time constant should not be set too high because the
same signal is also used for minimum and overcurrent supervision
of the field exciter unit.
F1 CURR TC (1307)
F2 CURR TC (1504)
Functional Software description
4095 = rated current
4710 = 115% of rated current
(scaling 1 = 0.01 s)
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