Baker Hughes Apollo 3, Руководство пользователя

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Figure 89: Underload Menu-Screen 2
The Apollo underload detection is not a simple threshold/trip delay trigger. It is actually formed by a
combination of the Pre-Trigger and the actual Underload trigger. Apollo shuts down the motor on underload
to prevent motor overheating (low load implies insufficient fluid movement past motor for cooling). A simple
threshold to detect underload would fail to protect the motor in the following condition.
If the load occasionally bumps above the threshold, even for a fraction of a second, the trip delay
timer will be reset. In effect, the motor can be run in an underload condition indefinitely without
stopping-as long as there are occasional bumps above the underload threshold!
In Apollo, the underload pre-trigger is used as the input for the underload trigger. The underload pre-trigger
filters the motor current data to ensure that momentary bumps of the current above the underload threshold
do not cause the underload trip delay timer to restart. Underload Pre-Trigger default operation is as follows:
• The Enable Timer is set for 10 seconds – the underload pre-trigger cannot activate until the drive has
been running for at least 10 seconds.
• The Set Trip Delay is set for 5 seconds – the underload pre-trigger cannot activate until the motor current
has dropped below the motor underload threshold for at least 5 seconds.
• The Clear Delay is set for 10 seconds – here’s where the underload pre-trigger does its magic. The
underload pre-trigger will not clear unless the output current of the drive is above the motor underload
threshold for at least 10 seconds. Thus, the underload trigger does not see short bumps in the drive
output current
– only those long enough to allow the underload pre-trigger to clear.
The purpose of the underload pre-trigger is to avoid the problem with a simple threshold.