Hi All,

Please answer the following questions

1) what is meant by high and low level wiring in MARK V?

2) please tell me about NEMA I standard? frequently used for MARK V.

3) Are there any LVDTs connected on the Electro Hydraulic Servo valve which controls GCV and SRV? for MS5371 turbine?

 

> 1) what is meant by high and low level wiring in MARK V?

This refers to the incoming field wiring cables and conductors. Low level typically refers to any circuit that operates at less than approximately 50 V (AC or DC). This includes 4-20 mA circuit, thermocouple circuit, LVDT excitation and feedback, servo-valve outputs, RTDs, etc.

High level typically refers to any circuit that operates at more than approximately 50 V (AC or DC). This includes 125 VDC incoming power, 120/220 VAC incoming power, solenoid outputs (if they operate at 125 VDC), discrete (contact) inputs (if they operate at 125 VDC), motor starter circuits, etc.

> 2) please tell me about NEMA I standard? frequently used for MARK V.

NEMA stands for National Electrical Manufacturers' Association, and the roman numeral designation refers to the type of cabinet (control panel enclosure) and its "weather proofness". In this case, a NEMA 1 cabinet is not weatherproof, and is convection-cooled. You can find more information using your preferred Internet search engine.

> 3) Are there any LVDTs connected on the Electro Hydraulic Servo valve which
> controls GCV and SRV? for MS5371 turbine?

The electro-hydraulic servo-valves themselves do not have LVDTs, but the devices they serve to position typically do, such as fuel valves and IGVs.

 

hi csa

thanks to your explanation in all about gas turbine and its more helpful to us.

if you allow i will ask some more questions about mark v

1) what is meant by MARK V?
what are the main difference between mark iv/v/vi/VIe and others?

2)is it possible where using others control system except mark v,vi,... to run the frame v GT

3)why the motor dives are named in prefix with Q and where i can get the device summary of tag list & description of tags? how i can identify the tags where it is used in gt.

4)i am working in frame v naphtha & hsd fuel fired GT, what is the meaning of DLN combuster, SRV ,GCV?

and finally,
5)how can i select a suitable processor Single or double or TMR type? is it based on cost or I/O's or any other things?

 

ananthbabu,

You're welcome for the information. While I get a little testy at times, I try to remember the patience of others who answered all my questions when I was starting out.

Mark X (where X is V or IV or VI or VIe of I or II) is the "generation" of Speedtronic turbine control system. The first GE heavy duty gas turbine control system was called 'Fuel Regulator', the next Mark I, then Mark II, and so on. The current generation is Mark VIe. The differences are primarily in the technologies used (analog, analog/digital, digital/analog, digital). Beginning with Mark IV TMR (Triple Modular Redundant) there were some changes made to GE's philosophy of gas turbine control. Mark V was the first to include a second (back-up) integral, independent electrical overspeed protection scheme that is still used in different forms in Mark VI and Mark VIe.

There are many other differences in the control system hardware--but the thing to remember with all of the changes to GE heavy duty gas turbine control systems is that the operation of the turbine didn't change over the years. Turbines and auxiliaries changed very little over, but the control systems have evolved as technology has evolved.

In my opinion, the troubleshooting "tools" available with each generation of Speedtronic has improved. By "tools" I mean the ability to monitor and trend and record operation and data to help with troubleshooting and maintenance. While the methods haven't always been easy to use, they have been improving.

2) Yes, there are many companies providing other, usually PLC-based (Programmable Logic Controller) control systems. The problem with these is that the several of the types of I/O used on GE-design heavy duty gas turbines are not generally used in most other industries and processes where PLCs are used. This means that converters have to be used which increases complexity and adds points of failure to the control system. I'm speaking about LVDTs (Linear Variable Displacement Transducers) for position feedback, and flame detectors (335 VDC power supply and feedback), and +/-10 mA servo valve outputs. In addition, shaft speed control and overspeed protection requires very high sampling rates, over and above those of some early PLCs. This has required some proprietary cards to be developed in the past for some PLCs.

While it's true that PLCs have lots of programming flexibility and it's generally easy to find multiple resources for programming and troubleshooting PLCs, the control schemes and algorithms required for electrical power generation are not very well understood by most PLC programmers and are not readily available in the libraries of most PLC softwares. I've seen some atrocious PLC programming attempts at droop speed control and CPD-biased exhaust temperature control. And even simple motor starter logic has been badly implemented in PLCs.

Speedtronic turbine controls are purpose-built control systems. They are not intended for use in meat-processing facilities or sewage treatment plants. You could use a Speedtronic in these applications, but it would be necessary to use converters and implement some control schemes in very crude form to make them suitable for a meat-processing facility or a sewage treatment plant. They're not designed for that. So, why take a PLC--that's not designed for combustion turbine control--and try to use it to control a combustion turbine and its auxiliaries? Why not use the control system that was purposely designed and built to implement the types of control schemes necessary for the application and the types of I/O used on the equipment?

3) Naming of devices and signals in GE-design heavy duty gas turbines has pretty much followed the same scheme for decades--though it's not very well documented in any book or manual. You just kind of have to learn how it works. There may be something added to the control.com wiki soon about signal names.

If you have a Mark V control system, there is a text file on the operator interface called LONGNAME.DAT which can be printed and referred to. It is very helpful--though not 100% accurate. If you have questions (not doubts--questions!) ask them here.

4) DLN means Dry Low NOx. It is a style of combustion system/fuel nozzle that reduces the formation of an air pollutant called NOx (Nitric Oxide). SRV mean Stop/Ratio Valve; the SRV is, primarily the stop/fuel shut-off valve for gas fuel (natural gas, usually). It has a secondary purpose also, to control the pressure downstream of the SRV in proportion to turbine shaft speed--the "ratio" portion of the valve name. GCV is the valve downstream of the SRV that controls the amount of fuel admitted to the turbine. By controlling the pressure upstream of the GCV (which is the secondary function of the SRV) the flow through the valve is more proportional to the position ("stroke") of the valve. So, the SRV is used to control the pressure at the inlet to the GCV so that valve position is proportional to flow (at rated turbine speed).

5) How can "you" select a suitable processor? Are you thinking of upgrading your turbine control system? If so, you should be knowledgeable about what is most important in operating the turbine at your site. If you need to keep the turbine running as much as possible, only planning to shut down for mechanical maintenance, then you want a control system where components that might fail can be replaced without shutting the turbine down. A DUAL or Triple Modular Redundant system is the best for this type of requirement. If your site or process can be shut down for control system maintenance or replacement of failed parts without adverse effects to some other process or revenue stream, then a less expensive SIMPLEX (single) processor-based control system could be used. It's all about what your needs are, primarily, and then about what your budget can afford. (Actually, it will most likely be about what the salesperson can make the person who signs the contract believe.)

It's been said many times before on control.com: A PLC can be programmed to do just about anything. It's the after-installation service and support that really determine the value of the equipment. Ask the vendors you're most thinking of purchasing equipment from to provide reference contact information for similar jobs they've recently completed--and not just one or two references. And, then don't be afraid to contact these references and possibly even visit their site, if possible, to find out how they really feel about the equipment and support and the documentation. It's very important to do this, but most sites don't do it.

GE replaces lots of PLC-based control systems, sometimes only after they've been running for a couple of years or less, because of poor support during and after the installation.

Hope this helps!

 

thank you very much csa for your elaborated explanation about my query. its more helpful to me.

 

Good day all,

I have one more question related to MARK V. we had a trip for one of our frame-5 gas turbine units and after investigation we found that the cause of the trip was "the deviation of 5 exhaust thermocouples than the average exhaust reading." further investigation yielded that the root cause behind the deviation of those 5 thermocouples is the overheated MARK V thermocouple input card (location#2 in <R>) to which all the 5 thermocouples are connected.

We had this issue in more than one unit in the same day and it was clear that the real root cause of those cards to start giving wrong reading in the control room temperature (115 Deg F) as the A/C unit was malfunctioning at that time.

The problem was cleared after resetting/replacing that thermocouple input card and of course fixing the A/C unit.

My question is what is the maximum temperature that mark V control system cards can withstand including (processors, I/O cards & Thermocouples cards)

Thank you in advance

 

Hello,

I don't have access to the Mark V Application Manual, GEH-6195, at this writing but I believe the minimum and maximum temperatures are listed there.

However, as you've noted each processor calculates its own cold junction compensation. So, if one or more processors sees much higher or lower ambient temperatures then the cold junction compensation will be adversely affected. I'd previously seen this occur when an air conditioner vent was blowing directly on <S> processor, causing its cold junction compensation to be significantly different from <R> and <T>.

So, the minimum or maximum temperature is an "average" value for the entire panel.

 

Dear Ali,

In general at about 110 deg.F (43 deg.C) we used to get alarm. So we could take some preventive measures. What is your site setpoint?

I too waiting to know the cards withstanding temperature limit.

Take care
G.Rajesh

 

The card did not necessarily fail because of the high temperature. The trip was caused because the cold junction compensation temperature of the one control processor was higher than the other two control processors. There is no SIFT or voting for the cold junction compensation temperatures of the three control processors. (<C> also calculates its own CJ temperature.)