54 ESP program features
Underload ride through recovery sequence
The Underload protection function protects the motor casing in the presence of fluid
flowing over the motor cases. When an ESP is pumping the fluid (oil), gas might be
ingested by the ESP. This results in a reduction or removal of a fluid flowing over the
motor casing which results in overheating of the motor. The presence of gas can be
inferred by the detection of an underload condition.
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.
The table below describes some typical underload recovery sequence operation.
If the condition continues after the underload ride through recovery sequence is
completed, the drive generates a warning or a trip.
Sequence Operation
1 A-Normal operation -> B-Underload -> C-Back to normal at higher
speed -> A-Original speed
2 B-Underload -> D-Not ok at higher speed -> B-Underload ->
E-Lower speed helps -> A-Original speed.
3 B-Underload -> D-Not ok at higher speed -> B-Underload -> F-Not ok
at lower speed -> Trip to fault.
I
mot
(Amp)
C
D
B
F
E
A
f
mot
(Hz)
Motor underload trip
current curve
Ideal motor current curve
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