In order to ride through the gas lock and avoid tripping, the drive should increase
the speed reference and thus increase fluid intake in proportion to the gas fraction.
You can also reduce the speed for sometime in order to damp the gas stream. The
drive can be configured to perform these speed change routines automatically in
response to detected underload condition.
The figure below illustrates the work points of underload protection curves.
I
mot
(Amp)
f
mot
(Hz)
Ideal motor
current curve
Motor Underload
trip current curve
The table below describes some typical underload recovery sequence operation.
OperationSe-
quence
A-Normal operation → B-Underload → C-Back to normal at higher speed → A-Ori-
ginal speed
1
B-Underload → D-Not ok at higher speed → B-Underload → E-Lower speed helps
→ A-Original speed
2
B-Underload → D-Not ok at higher speed → B-Underload → F-Not ok at lower speed
→ Trip to fault
3
If the condition continues after the underload ride through recovery sequence is
completed, the drive generates a warning or a trip.
The figures below illustrates various scenarios with underload ride through recovery
sequence.
58 ESP program features
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