I am interested if anyone in the community has experience of using Ovation for LM2500 control. We are reviewing the use of Ovation against Woodward. I am not convinced that a non OEM authorised solution is best. What are your thoughts?
For any kind of warranty/guarantee on the engine and power turbine, it's usually required to have a turbine control system that is approved by the GE Aircraft Engine group in Evendale, OH USA. Especially if the LM has any kind of DLE or is anything other than a SAC (Single Annular Combustor) engine. I guess some power turbine manufacturers or suppliers might not necessary feel that way, but most GG (Gas Generator) suppliers (including the OEM) seem to pretty much feel that way (they want an OEM approved turbine control system). It's mostly about speed of response of the control system to any "upsets" in engine and/or auxiliary operation (to protect the engine).
But, if you own the engine and don't have any warranties or guaranties from any supplier or service group then you're probably free to do just about whatever you want to the engine--and own the consequences, too.
Personally, I have never heard of an Ovation control system on an LM aero-derivative engine--doesn't mean there aren't any out there, just that I haven't heard of any.
On aero engines the system response and fuel metering accuracy is critical. Aero engines have fast transient performance requirements.
For example to protect against flameout and guard the compressor stall line.
For DLE aero engines the game is amped up.
There are specialized pressure transducers, protocols, metering valves, and algorithms for accuracy and fast response requirements on aero engines.
Many of which are also used on non-DLE or SAC engines as well to add that extra bit of performance. For example the fuel metering algorithms developed are also critical for consistent starts.
There are quite too many hardware and software features to mention that are purpose designed and qualified with GE Aviation
for an OEM control on LMs. Speed sensing technology is one key feature that general purpose PLCs do not have or have different design criteria for, typically being a "counter" module typically used for other purposes that turbine control.
The control loops and protection on an LM aero will also rely on a good calculated speed derivative, or rate of change (RPM/sec) for accel/decel transients as well as flameout protection when UV sensors are optioned off.
What I mean by good is ... fast but clean, not too noisy ... and these can be a mutually exclusive thing to some extent when computing a speed derivative. It can and is sorted with proper design and understanding how much to trade off these two criteria in an algorithm to do this. This has as much to do with fielded and design experience as it does with choosing the proper sense circuit, filtering, and algorithms.
Another key feature is the 5 to 10 msec recursion rates being much faster for speed loop and other critical functions.
This is coupled with fast inner servo (variable geometry i.e. VSV etc.) and fuel valve position loops 5 to 10 times faster than the speed loop.
On LM2500s Woodward uses a 5 msec software execution rate for the PT speed loop. This can be the difference it getting an overspeed trip or not as the free Power Turbine and typically lighter generator Inertias on LM2500s make this a challenge.
It will be the difference in keeping the engine running on a breaker open ready again to re-close with minimized impact to availability.
... or even in the case of a throttle step cut back on compressor drives or marine propulsion engines to avoid a process upset or for an emergency maneuver.
Woodward as a certified OEM supplier of controls and fuel systems to GE on LMs maintains and updates standard aero core fuel control software per engine type to include for example
LM6000: PA, PB, PC PD, PF, PF+, PF2,
LM2500: PE, PH, PJ, PK, PR RC, RD, RA, RB
LM1600 PE, PH and LM500 PEM
including Marine, SynGas, Coke Oven Gas, Other Unique / Low BTU fuels and blends, DLE 1.0, 1.5, 2.0 etc.
Woodward updates and add the newest features, improvements, and requirements for the LM Aero’s.
The changes are continually re-certified with GE Aviation in a rigorous test verification process.
Application experience is also of key importance and the number of LM units and history at Woodward is extensive.
Take a look at this article.
The two LM2500 Generators and steam turbine Woodward controls were replaced during this outage with a non OEM-certified control.
Reaching out to other LM users groups and getting feedback is also beneficial. WTUI for example.
I totally agree with WoodyGuy that aero-derivative control requirements are very stringent and specialized. Emerson's Ovation control application for LM has been designed to meet these requirements and has been applied to dozens of GE LM, P&W FT8, and other aero engines (both SAC and DLE versions).
Ovation has native I/O modules that are used for speed measurement, variable geometry, and stall protection. Ovation turbine control systems are tested to confirm that the response conforms to OEM requirements. Variable geometry loops are calculated every 1 msec. Control loops are segmented into the required frame rates needed to run fuel control and protection programs for LM engines. During customer witness tests at the Emerson factory, Emerson uses an engine simulator to demonstrate speed stability and grid frequency response, full load rejections, flameout, etc.
WoodyGuy is also correct in pointing out that aero-engine control is the most complex variety of GT control. Emerson has experience with hundreds of GT controls retrofits and the Ovation hardware / software platform is used now by many fleet owners who have a combination of heavy frame and aero-derivative engines.
If you have additional questions or would like to consult directly with one of our turbine engineers, feel free to drop us a note at: