Rockwell Automation T6050 SurgeGard Incipient Surge-Conditioning Module - Manual (Page 42)

ICS Triplex Turbo Machinery Control
14
Field Surge Testing Procedure
In a typical scenario for surge testing a compressor, it is necessary to override some of the protection
features of an anti-surge controller (with the T6200 & T6300 controllers these override actions are
automatically enabled; already pre-configured). This requires that the controller should be switched
to manual mode, and the Surge Control Line (SCL) transgression feature be disabled. The
compressor can now be throttled in order to emulate a potential process upset, or reduced capacity.
Once instability is detected in the compressor instrumentation, the anti-surge loop (ASPID) can then
be switched to automatic mode, in order to open the recycle valve rapidly before the machine
actually reaches the Surge Limit Line. The Incipient Surge control loop can now be used to assist in
detecting the on-set of surge. It is important that the Incipient Surge PID should also be placed in
MANual with a self tracking feature, so that its Output will remain at 0%. The signal from the T6050
SurgeGard™ should now be observed on a trend display or a wave-form analyzer plot, so that the
oscillations of the selected parameter, (motor current, flow, suction/discharge pressure for example)
can be monitored. The T6050 SurgeGard™ will integrate these oscillations, to produce a process
value (PV) proportional to the signal noise plus process noise as the compressor approaches surge. It
is normally necessary to adjust the gain of the T6050, in order to have the right amount of sensitivity
for each compressor installation. A T6050 that is set too sensitive will result in early opening of the
recycle valve even though the compressor may be far away from surging.
Once the optimum gain setting has been determined, the trend or wave-form analyzer plots can be
used to repeat surge testing at different base conditions. Each test can be terminated at equal signal
amplitude occurrences, without any necessity to risk actual surge damage by throttling the
compressor too far. An accurate surge limit line can now be established safely and in a repeatable
manner for all future surge tests. Once surge testing has been completed, the anti-surge controls can
be restored to full operating conditions, the Incipient Surge PID Loop can be placed into automatic
mode, with a test-proven set-point for future incipient surge override duty. It is also recommended
that the Incipient Surge PID control block should feature a set-point balance and ramp (standard in
the T6100, T6200 & T6300), so that the set-point will remain at the entered value, as found during
the tests.
The Incipient Surge PID Loop output must be ignored during start-up cycles (configured such that
the Incipient Surge PID loop switches to AUTOmatic only after the start-up timer has expired;
already pre-configured in the T6100, T6200 & T6300), due to the unstable conditions which may
manifest themselves until the machine has stabilized and started to build some head pressure. For
motor I or KW incipient surge parameters, it is also important to use a high signal fallback feature
(FB function; already pre-configured in the T6100, T6200 & T6300), in order to mask out motor
transducer noise from adjacent machines starting or stopping, when powered from the same electrical
power grid.