Hi

In our power station we are using diesel engine as starting means for gas turbines.

The maximum speed of the diesel engine given by the manufacturer is 2100 RPM while the gas turbine speed reaches 3000 RPM then the diesel engine disengage from the turbine.

can you please explain how the diesel engine speed exceeds the max rated speed?

 

Hi,
Have you looked at the Starting Means Piping Schematic (P&ID) to see that the diesel engine is not directly connected to the turbine shaft via the Starting Clutch? There is a hydraulic torque converter between the output of the diesel engine and the Starting Clutch/turbine shaft. (Actually the turbine side of the clutch is connected to a shaft of the accessory gear box that is connected directly to the accessory coupling that is connected directly to the turbine shaft).

So, the diesel is driving the torque converter which is then driving the turbine shaft. The output speed of the torque converter can be higher than the input speed of the diesel and still transmit torque to the turbine shaft.

The Piping Schematic drawings (P&IDs) are one of the most important groups of drawings for any gas turbine. GE-design heavy duty gas turbines use Piping Schematic drawings (P&IDs) to describe the various systems and control devices and instrumentation used on the unit (turbine and drive device). They are critical to understanding how the unit operates, how it's auxiliaries operate, and how the unit is controlled, monitored, and protected. Most questions like this can be answered by reviewing the Piping Schematic drawings.

Granted, the Starting Means Piping Schematic drawings don't actually state precisely what the input and output speeds of the torque converter are, but it's pretty clear from your question that you believe that the diesel output shaft was directly connected to the turbine shaft--and it's not, and that's clearly shown on the Piping Schematic.

A torque converter is another name for a hydraulic pump which can have a variable input speed for a relatively constant output torque. In the case of using a torque converter between a diesel engine and an accelerating turbine shaft, the torque will be fairly constant as the turbine shaft speed increases and then at some point as the turbine shaft speed increases the torque output of the diesel/torque converter decreases. When the turbine shaft speed "over-runs" the torque converter output shaft speed, the clutch opens and that sends a signal to decelerate/shutdown the starting means (the diesel engine in your case).

I've been to many plants where the operators and technicians have never seen the Piping Schematics for the unit. I've also been to plants where the Piping Schematic drawings are either available on a stick or in a folder, or have been laminated in plastic and placed in a folder on the control desk in the control room. Guess which plants have better operating reliability and availability?

Many people complain that the Piping Schematics are difficult to understand; they don't recognize the symbols. The symbols used on the piping schematics are fairly common symbols, and there should be a Piping Symbols drawing provided in the Instruction manual if there are any questions.

For anyone wanting to understand how the systems on their unit operate, and thus, how the unit operates, the Piping Schematic drawings are key to that effort. They aren't difficult to understand, it just takes some time studying them to get familiar with them. Don't start with the most complicated one (the L.O. Piping Schematic); but do start going through them. Make your own copies, and then you can make notes on them to help you understand them. If you have questions, we have answers!

And, don't forget to read the Notes on the drawings. VERY often the Notes contain some very important, even critical, information that is very important to the configuration and proper operation of the field devices and instrumentation, and therefore the unit.

 

I appreciate your efforts in reply to my question

P&ID diagrams are available in our plant but as you stated I am one of those who finds it difficult to understand these line drawings. it can tell me how things are assembled together but it don't tell how it works That's why I not use them most of the time.

I really want to know how did you build your knowledge about this subject to take it as guide for me in understanding the operation of GE gas turbines.

 

If you want to understand GE-design heavy-duty gas turbines, understanding the Piping Schematics (P&IDs) is more than 75% of the battle. Full stop.

I hear this all the time, that they are difficult to understand. I think that's because most people don't consult them unless there's a problem and it's frantic at that time and they are frantically searching for answers and they're not readily apparent at that time.

Pick a time when you are not busy and won't be interrupted. Have a copy of the drawing(s) and a pencil; I recommend the largest copy you can make (B-size, or A5, or whatever your photocopier can make). Pick a very simple schematic, say Hydraulic System; not much to that one. Or, the IGVs; not much to that one, either. Flow is from left to right, input to ouptut, almost 100% of the time. And, read the Notes first. Then start working through the drawing, one line at a time, beginning from the left. Make notes with your pencil.

If you have questions, we're here to help answer them.

But, don't try to understand the drawings when you're troubleshooting a problem and need to find answers/solutions in a hurry. It's just not the right time.

When you've finished reviewing a drawing and making notes on it, go out to the unit and find the devices shown on the drawing. In the case of the Hydraulic System, a lot of them are located in an area of the L.O. Tank tank that requires removing many bolts on an access cover. So, that one is best left for some time during a shutdown or maintenance outage, but, do it. You need to find things like the Transfer Fill Valve, and Filter Air Bleed Valve, and the pressure regulators (I'm presuming the unit has both an AC motor-driven Auxiliary Hydraulic Pump and an Accessory Gear-driven Hydraulic Pump and so will have two pressure regulators).

Do this for each system. I call it "tracing systems" to find each devices on the Piping Schematic Drawings (P&IDs) and you will learn volumes about your unit and be a much better operator and technician. And, to be a good technician one also needs to be a good operator, to know how things are supposed to work so that one can determine if they are working properly or not.

When I was first assigned to learn about GE heavy-duty gas turbines, I was sent to Mark IV Speedtronics training--without ever knowing a thing about gas turbines or GE gas turbine operation or control philosophy. We learned all about FSR and IGVs (I'd never seen "one") and 20CBs and 33CBs and 20FGs and 88CRs. We learned how to force logic and how to change Control Constants and edit sequencing. But, I know nothing about how a gas turbine and its auxiliaries operated or how they should operate or what the philosophy was behind different control schemes, redundancy and the lack of redundancy.

I went to the field and was assigned to work with a very knowledgeable field ENGINEER (someone who thinks logically and understands or tries to understand what they were working on, anticipates problems, and is more proactive than reactive). He told me if I wanted to understand gas turbines, I had to learn the systems and to learn the systems I needed to learn the Piping Schematics (P&IDs).

And he was right. Completely and utterly right. Once I understood the systems and auxiliaries, then most of the control system training fell into place. I knew what the devices were that were being energized and de-energized, and sensed, and had current applied to them. By actually going out to the turbine and finding all of the devices (difficult at first, but VERY necessary and informative), what I call "tracing systems", even more things became clearer and things really started to make more sense.

So, learning about the Speedtronic should always be secondary. Learning about the turbine, driven device, and auxiliaries that should be first in the progression, and then about the Speedtronic.

But, as has been being said in another thread on control.com, "Management" just believes that if one learns about the Speedtronic they will learn about the turbine and auxiliaries. That's the long, hard way; trust me. And, it's very short on details and has a lot of holes in the understanding that one can gain from this method.

Learn the Piping Schematics, learn where the devices are, and do this when it's not in the heat of troubleshooting a trip or a forced outage. Then, when there is a trip or a forced outage you'll be prepared and know where things are and how they are supposed to work.

And use control.com to help you learn those systems and understand those devices. The only dumb question is the one that doesn't get asked. I'm more than willing to help people learn by understanding Piping Schematics because it's the best way.

Speedtronic systems are not simple, but when you understand a couple of things (the field devices and instruments connected to them and the systems they are located in, and some basic GE-design heavy-duty gas turbine controls philosophies) they suddenly become a lot simpler. Without understanding all of these one cannot really be a good technician or be a successful technician without repeatedly being very lucky. But, there will be an occasion or more when luck just isn't on that person's side.

Just because something is difficult to understand doesn't mean it's not necessary or important. In this case, the Piping Schematics (P&IDs) are extremely important, vital and critical, even, to a solid understanding of GE-design heavy-duty gas turbine operation and troubleshooting. Without understanding them, committing them to memory, actually, and without being to find the devices on the unit when it's crunch time, then knowing everything about the Speedtronic and how it works is pretty useless.

Theoretically, just about any control system could be used to control just about any process--if the person applying and configuring and programming the control system knows exactly what is supposed to happen, when it's supposed to happen, how it's supposed to happen, and why it's supposed to happen. It's not the control system that defines the way the process is operated, is the process that defines the way the control system operates.

Sure, there is Mark I, Mark II, Mark IV, Mark V, Mark Ve, Mark VI, and Mark VIe Speedtronic control systems--but they almost all interface with the same auxiliaries and systems to control the turbines in pretty much the same way. That's one of the beauties of the GE-design family of heavy-duty gas turbines. Basically, they just scaled-up their design as they built bigger and more powerful machines. But, the basic systems changed very little over the decades and even over the generations of control systems.