We intend to retrofit the control system of our gas turbines. (They are GEC gas turbines)

I wonder if one could give me more information about the systems that normally implemented for this issue. In other words which options are mostly used in this job?

We consider control and fuel system upgrading. My main concern is about the ESD signals of the turbine, that which configuration is mostly recommended? I mean a separated system/PLC from the control system is considered for that purpose or the ESD signals are included in the same PLC which is responsible of the control system.

I do appreciate your concern

 

The protection for the turbine itself can be included into control system like low lube oil pressure, high exhaust temperature and so on. There will be bunch of protection which come from field devices like limit switch or transmitter.

The overspeed and generator protection should be independent from control system as they requires more fast response to prevent overspeed of turbine and generator failure.

which country are you in now?

 

What the SIL level of the PLC/control system?

If the ESD PLC is independent of the control system, what level of the SIL is required for?

The turbines are driving the gas compressors.

Thank you for your concern.

 

There are a lot of control system integrators that will configure a PLC (Programmable Logic Control) system for use as a turbine control system. While PLCs are excellent for the majority of gas turbine control functions (turning on pumps and fans and energizing solenoids and annunciating alarms), they generally have to have special components to be able to interface with some of the more important, and critical, gas turbine I/O.

Examples include:

--LVDT excitation and feedback
--bipolar servo-valve current drivers
--flame detection

and, most importantly.
--speed detection.

Most PLC scan rates are not fast enough on their own to perform some speed detection and protection, for even normal functions (excluding overspeed protection). So, there is usually some kind of high-speed speed detection card or interface which has to be used, which is sometimes a proprietary card which can only be obtained from certain sources (kind of defeats the purpose of using an 'off-the-shelf' PLC).

Most PLCs can generate the high-frequency, low voltage excitation required for LVDTs, and can't process the differential voltage feedback--without some kind of interface module.

Most PLCs can easily generate 4-20 mA outputs, but not -10 mA to +10 mA outputs that many GE-design heavy duty gas turbines use for valve positioning. So, here's another interface module that's required.

Best to stick with a control system that's designed for a turbine and its auxiliaries, not one that's being adapted for controlling and protecting a turbine and its auxiliaries.

Lastly, it's really the experience level of the control system provider that's most important. How well does that provider understand droop- and isochronous speed control? How well does that provider understand compressor discharge pressure-biased exhaust temperature control? How well can that provided integrate speed control and exhaust temperature control so that transfers between them are smooth and "bumpless" and allow the turbine to produce as much power as possible under expected operating conditions while still protecting the hot gas path parts and the compressor and optimizing parts life?

That's where the real value of a control system comes in: How it's configured and programmed to control and protect your turbine.

ESD devices (fuel shut-off solenoids; electrical overspeed protection; etc.) can and have been accomplished in a variety of methods, some better than others, and some downright poorly. There have been some excellent PLC programmers write some very poor code for turbine control because they just don't understand turbine control, turbine operation, and turbine control philosophy.

So, it's been said many times before on control.com: Hardware is the least of your problems when it comes to choosing a control system to retrofit an existing control system. It's really down to the ability of the control system provider to implement and execute the control system to control and protect your process, which in this case is a turbine and its auxiliaries. Look for an experienced control system provider, ask for references (nobody ever does this, and many regret not doing so) and talk to the references about execution and commissioning and spare parts and drawings and documentation and after-installations support.

Again, most PLC hardware can be adapted to do just about anything. It's the total system configuration, installation, commissioning, and package that really matters.

While dealing with the OEM may not be very palatable to some people, their control system is still designed and configured and programmed for optimum operation, control and protection of a turbine and its auxiliaries. They may not always be the best on execution (installation and commissioning), but their hardware and it's configuration and programming and the support from their engineering is usually better than most control system integrators who will package a PLC for turbine controls. If you are intelligent about the planning and execution of your turbine control upgrades you can achieve good results with the OEM during installation and commissioning.

I'm beginning to believe that many commissioning problems experienced during commissioning are the result of trying to execute a controls retrofit at the same time that a major maintenance outage (major inspection, or hot gas path inspection, for example) is also being performed. Combining the two are like mixing oil and water, the results are unpredictable and usually undesirable. And the schedules are never properly prepared and there's too little time for necessary commissioning activities once the mechanical work (which is usually behind schedule) to be completed. So, shortcuts get taken and the results are less then desirable.

When a controls retrofit is being done, one needs to have access to all the field devices and instruments so that loop-checking and commissioning can be done in a logical and orderly fashion. If this is attempted during a maintenance outage when many field devices and instruments are disconnected and L.O. and Hydraulic systems are not available, this can lead to lots of problems.

So, take a "big picture" approach when planning for a turbine control retrofit. And, choose a supplier with a demonstrated ability to provide a system that seamlessly integrates with the existing field devices and instruments and doesn't have a lot of interfaces to accommodate them. And one that has demonstrated an ability to execute and commission the system without issues requiring weeks or months to resolve.

Best of luck, and let us know how you fare in your search.

 

Let's assume that you will choose for GE's MKVeS control and SIL approved protection system.

The prime protection for the Gas turbine process related signals (seismic, temp. control etc.) will be handled by the part of the MKVeS separate processors ( actually the MKVe part) and the SIL required protection will be handled separate by dedicated processors (the "S system side" of the MKVeS) and the associated redundant IO's. You may consider to interface all the Fire and Gas signals as well as the fuel gas conditioning system related protections.

MKVIeS is "Alive and Kicking".

Good Luck...
A. Oztas

 

I work for Turbine Controls Ltd. This company was formed by a number of ex-employees of GEC Gas Turbines and we have a lot of experience of control system retrofits on this type of machine.

We generally use a PLC for the control and monitoring. The processing power of PLC's has greatly increased in recent years and so have adequate processing speed for Gas Turbine control. Typical iteration rates of less than 10msecs for speed governing are easily obtained.
The ESD signals are generally wired into the PLC and a hard-wired system in order to give the required system integrity.

Have a look at our web site at www.tcluk.net for additional information and ideas.

Hope this helps. [email protected]