Hello everyone,

Myself working in a co-generation plant with 60 MW(3x20MW) generation with three gas turbines with HRSG boilers. I want to learn about the starting engine (diesel engine) functioning like how it helps to get the gas turbine to its self sustaining speed. In this effort I have collected some drawings of the diesel engine , copy of which is enclosed herewith. It will be of great help if anybody can throw some light on the functioning of control system of the diesel engine.
Details of the deisel engine : Make: Cummins Model: KTA 1150 C,RPM: 2100, HP 465
Gas turbine : MS5001 simple cycle, single shaft Gas Turbine with 20 MW generation capacity, control system : Mark VIe

I have got great help from this forum to enhance my understanding, thanks for all the help.
thanking you all
jagriti

 

Hello everyone,

Myself working in a co-generation plant with 60 MW(3x20MW) generation with three gas turbines with HRSG boilers. I want to learn about the starting engine (diesel engine) functioning like how it helps to get the gas turbine to its self sustaining speed. In this effort I have collected some drawings of the diesel engine , copy of which is enclosed herewith. It will be of great help if anybody can throw some light on the functioning of control system of the diesel engine.
Details of the deisel engine : Make: Cummins Model: KTA 1150 C,RPM: 2100, HP 465
Gas turbine : MS5001 simple cycle, single shaft Gas Turbine with 20 MW generation capacity, control system : Mark VIe

I have got great help from this forum to enhance my understanding, thanks for all the help.
thanking you all
jagriti

Below are a couple of documents that will help. I cannot find anything for the Cummins engine as that is very old and was replaced by the Detroit engine which was bigger (600HP), the operating system is pretty much the same though.
Hope this helps. Please ask if you need more specific help

 

jagriti,

Methinks the GE-design Frame 5 heavy duty gas turbines at your site were not packaged by GE, probably by one of the several licensed Business Associates of GE (including, but not limited to BHEL, John Brown, and others). I say that because of the style of the drawings you provided; they are not like typical GE P&IDs--very similar but not identical. I also suspect the units are fairly old (20 years old or more), because of the diesel engine control system.

Be that as it may, I'm hoping glenmorangie can help with any corrections as he's seen more BA turbines than just about anyone I know. But, I can get this discussion rolling.

A heavy duty gas turbine cannot be started from zero speed by simply admitting fuel and energizing the ignitors (spark plugs). A source of torque to spin the turbine-generator shaft up to minimum firing speed is required. And that source of torque cannot be directly coupled to the turbine-generator shaft--because the torque provided by a diesel engine at zero speed is zero. So, a starting means must be able to (itself) get to a speed that is capable of producing the torque required to accelerate the turbine generator from zero speed while at the same time allow the speeds of the starting means AND the turbine-generator shaft to differ.

The torque converter is the method by which the speeds of the starting means and the turbine-generator shaft can differ--it provides a hydraulic coupling between the starting means and the turbine-generator shaft. The starting means can run at whatever speed it needs to run at while the turbine-generator shaft is being accelerated from zero speed to firing speed and eventually all the way to self-sustaining speed. (Even when flame is established in the turbine and there is hot combustion gases flowing into and through the turbine section there is not enough energy being derived from the expansion of those hot gases in the turbine section to keep the turbine shaft spinning without a torque assist from the starting means.)

There's another very important part of the starting means which is necessary to help break the turbine-generator shaft away from zero speed during starting: the hydraulic ratchet mechanism. For GE-design heavy duty gas turbines equipped with hydraulic ratchet mechanisms the starting means, through the torque converter, does not have enough torque to overcome the inertia of the turbine-generator shaft at rest and start it accelerating. When the unit is STARTed, at the appropriate time the hydraulic ratchet mechanism is started. If you've observed the hydraulic ratchet mechanism in service when the unit is on COOLDOWN you will have noticed that the hydraulic ratchet mechanism kinds of "bumps" the turbine-generator shaft through it's 45 degrees of rotation. It's those little "bumps" that help the starting means accelerate the turbine-generator shaft during starting. Again, if one tried to use only the starting means and torque converter to break the turbine-generator shaft away from zero speed there isn't usually sufficient torque available to overcome the turbine-generator shaft inertia to get it spinning; and the hydraulic ratchet mechanism is the device that supplies that "bump" that helps the whole thing get spinning.

The diesel you have is an older diesel, so it's presumed the Mark VIe turbine control system being used is an upgrade, or retrofit, of an older turbine control system. Not really an important distinction, unless the reason you are asking about the starting means is because the unit is now experiencing starting reliability issues since the Mark VIe was installed and commissioned....?.?.? OR, the diesel has been recently serviced and refurbished and the unit is now operating slightly differently (or worse) than before and the Mark* is being blamed for the problem. The instructions provided by glenmorangie are for newer diesels with ECMs (Electronic Control Modules), which receive (usually) a speed reference signal from the Mark* and the ECMs adjust the fuel as necessary to make the diesel speed equal to the Mark* diesel speed reference. The diesel speed "control" mechanism on your unit doesn't really know what the diesel speed is or should be. The diesel speed is strictly a function of the adjustment of the solenoid stops on the fuel rack mechanism (the solenoids being 20DA-1 and 20DA-2). When the diesel is being serviced one of the things that needs to be checked is the diesel speeds attained when the solenoids are energized, and then the stops, if need be, should be adjusted to make the actual diesel speed as close to the desired values as possible.

Here's the problem with that description.... GE does not usually publish those speeds in any document they provide with the units they package and sell. And, quite often, the licensed packagers of GE-design heavy duty gas turbines don't usually publish that information either. The ONLY place I've ever seen that information published (supplied with new unit documentation) is in the GE document ("drawing") called the Device Summary. Once on a VERY old Frame 5 unit I did see the diesel speed settings published in the document ("drawing") called the 'Control Specification-System Settings'--but only once. Pretty important information, though. Most diesel engine mechanics and services companies which provide diesel engine services don't know those speed setpoints either, relying on the as-found solenoid stop settings. BUT, those experienced and knowledgeable diesel mechanics DO KNOW what the typical rated speeds of the diesels supplied as starting means are--and that can be extremely useful information. What every site with diesel engine starting means should be doing after reading this thread is using a proper tachometer to measure the diesel speed the current, as-found speed settings of the diesel should be measured and recorded and the Mechanical Department should have a copy of those settings (since they will the ones working on the diesel or working with the diesel mechanics) AND the Instrumentation & Controls Department should also have a copy of the settings so they can help when the Mechanical Department can't find their copy of the settings.

I'm probably approaching the 10,000 character limit imposed by the new Control.com forum system, so I'm going to stop at this point, and when I next post we will start discussing the starting sequence--as best I can without actually being able to see the application code running in the Mark VIe.

Hope this helps!!!