User guide

13-14
FlexPak 3000 DC Drive Software Reference
13.4 SCR Diagnostics and Adjusting Open
SCR Sensitivity
Under normal drive operation, the load carried by each
SCR
is relatively equal, as
shown in figure 13.1.
If one or more
SCR
s fail to turn to on, a unique pattern of insufficient or missing current
pulses results, as shown in figure 13.2.
Open
SCR
diagnostics detects
SCR
s that are not conducting by analyzing the level of
current produced by each
SCR
pair firing. If one or more
SCR
consistently fails to
produce current at a level approximately equal to other
SCR
s that fired, the drive
concludes that an open
SCR
has occurred.
The open
SCR
diagnostic calculates the percentage deviation of current feedback for
each pair of
SCR
s from the average current feedback. The percent deviation must
exceed the value set for
OPEN SCR SENSITIVITY
(P.600) before the diagnostic proceeds
to the next part of the diagnostic.
In the next part of the diagnostic, deviations from the average current are integrated
over time to eliminate transient effects from the calculation. When the integration
reaches the value of
OPEN SCR TRIP THRESH
(P.601), an open
SCR
fault is generated.
If you are experiencing nuisance
SCR
faults, you can use these parameters to increase
the tolerance to conditions that could trigger an open
SCR
fault.
Figure 13.1 – SCR Armature Current During Normal Operation