8/16/2019 MK6e Control System Checks

1/4

Phase 1 - Plant Instrumentation and control system commissioningThis mostly involves with the field instrumentation and the actual controller. Most of the critical systems and some of the non critical systems will be operational, commissioning and testing guys make sure that they work perfectly ( or fake it :P in some cases ).

Step 1 - Divide the turbine control into different subsystems - this is when the plant PID comes into play. The PID's make the job easier and does the subdivision for you. In a Gas Turbine system the different subsystems will look like this.

Scheme for lube oilScheme for cooling and sealing airScheme for trip oilScheme for cooling waterScheme for starting meansScheme for liquid fuelScheme for GCV/SRVScheme for atomising airScheme for Hydraulic oil supplyScheme for IGVScheme for flow inlet and exhaustScheme for compressor washing

Scheme for control devicesScheme for Fire Protection

Step 2 - Make a list of all instrumentation points (DI/DO, AI/AO, control actuators, etc) connected to each subsystem - Again its PID to the rescue. PID will have all field instrumentation (and also control room instrumentation) laid out. All you have to do is to segregate it into DI/DO, AI/AO, etc. A sample list for lube oil is shown below

Scheme for Lube oilLube oil pressure switchLube oil temperate switch

lube oil pressure indicatorLube oil temperature indicatorLube oil tank vacuum indicatorLube oil level indicatorLube oil low switchLube oil high switch etc ....

Step 3 - Make a "protocol sheet"/"checklist" - Once you have all the instrumentation points segregated the next important thing is to make a protocol sheet. A sample protocol sheet "row" for a pressure switch is given below.

SLNo Field ID Control system Tag Field Inspection connection health Loop healthPoint health Remarks

Here Field ID - Field ID as given in PIDcontrol system tag - point tag corresponding to the field instrument as in the control systemField inspection - visually inspect the filed instrument for any damage and tick if it is okConnection health - this is optional for new commissioning but important for maintenance. Most of the problems are because of bad wiring. Most if not all instrumentation have a standard connection specification. Checking the health of the connection wires though important is often time consuming and people skip it. Onc

8/16/2019 MK6e Control System Checks

2/4

e again this is recommended.Loop health - This means that you test the control loop till the control systemwithout the field instrumentation. ie if a digital point you short the potential free contacts or if analog inject a 4-20 ma signal , or if you are using a field bus device , you can do this without disconnecting the instrument with the help of fieldbus testing devices.

Point health - This the over all point health , ie you test the loop with instrument. sometimes it is possible to test the instrument on the field itself. likea pressure switch where compressed air is injected till it turns on or a limit switch where all you have to do is to is to push the small switch actuator, but in some cases it is not possible , like a temperature switch which needs a external heat bath calibration. In either case you declare this ok if either of the above is done depending on which point you are testing.

remarks - Boast you success of having tested a difficult loop here :)

I gave a sample for Digital input, the same can be applied to analog input. In output points you do the same expect that instead of looking at the control panel for the input to come , you force the signal in the control room and look in the field if it is working or not. the rest is the same. for actuators , the process is essentially the same , you can consider a an actuator as a output with a feed back input so you check both at the same time. for example in a servo you force a current ( output point) and see the servo movement (an input point) etc.

by the end of this step , you will be having a lot of lists. if there are 10 subsystems and each subsystem has at least one DI , DO , AI , AO and actuator you will be having a total of 50 separate sheets. This seems like a lot of work but believe me this is what is going to save you in the end.

step 4 - execution - Yes once you have completed the first three steps and havegathered a good group who are willing to do whatever it takes to get the job done ;) you are ready to proceed to execution of the plans. as i said you have 50 sheets left to fill up , proceed sheet by sheet. If you have the liberty of a lot of manpower most of it can be done concurrently. at the end of the execution of the 50 blank sheet you started with , thumb rule is at least 90% should have "success / checked ok" marked in the remarks column ;)

Reply to this post...

0 out of 1 members thought this post was helpful...YES, this is helpfulNO, this is not helpful User PicturePosted by Process ValueControl.com Most Valuable Participant - 56 helpful votes. on 10 April, 2012 - 1:56 pmPhase 2 - Plant control logic testing and tweaking

by the end of phase 1 , you have almost if not all the plant instrumentation working , feeding picture perfect data into your control system to munch on. This phase is to make sure that all the control philosophy is implemented correctly.

Step 1 - Divide the control logics into different subsystems - Again in a well designed system the Field PID subdivision and control logic subdivision will be the same. And ideally each subsystem should be independent of one another with any dependencies explicitly defined. This is where GE systems comes crashing downon you like a boulder off a cliff. They do a reasonably good job of dividing the control system into different subsystems , but the dependencies are not well defined and a single point will be used in a 100 different places that it becomeshard to keep track on. But commissioning engineers do not havethe luxury to revamp the system , you just have to live with it and make it work. Which leads us to the second point

8/16/2019 MK6e Control System Checks

3/4

Step 2 - " STUDY " the control philosophy for each subsystem - Though this is ageneralization, i believe that this is where problem starts no one bothers about studying the control philosophy of the equipment they are commissioning. The end result is you do not know why the code is behaving in a way and worse you do not know how to fix it. GE provides a rudimentary documentation of the control philosophy, but plant auxiliaries will differ from site to site and as far as i know not documented anywhere. Yes this is a inherent disadvantage, but taking a look at the code will help. you can also consult site engineers/operators if theyhave a prior plant running , over the years i have come to know that they have a intuitive wisdom of what is good as they are seeing these machines every day. but the main thing is to know how the machine is supposed to to controlled. GE control can be subdivided into the following

Startup and shutdown control

Core controlflame controlcompressor discharge controlSpeed and load controlgenerator load controlExhaust controlIGV controlFSR control

FSRN controlFSRA controlFSRSU controlFSRSD controlFSRT controlVIbration protection controlsteam/water injection controlDLN burner controlDLN fuel mixing controlAUxillary controlLube oil controltrip oil controlHydraulic oil control

Starting means control (diesel engine)Hydraulic ratcheting controlfuel pump control (site specific)vent fans control

generator and excitation control

Trip and protection logics

Step 3 - Once again make a Logic check "protocol sheet" - Once you know the logic subsystems and the control philosophy behind them , it is time to make a check list. This can be tricky as this is not a straight forward one. for example lube oil control subsystem will have the following important logics

1. AOP start2. EOP start3. Lube oil temp high trip4. Lube oil pressure low trip5. Lube oil tank low alarm, etc .....

if you have studied the control philosophy well you should be able to differentiate the important logics well. the check list can look like this

8/16/2019 MK6e Control System Checks

4/4

Logic Description Signals involved Logic health Modifications needed Remarks

hereLogic description - a brief description of the logic under testSignals involved - tag Nos and descriptions of the important signals involved in the logicLogic health - How well you think the logic is performing up to the control philosophy , Individual testing may not be possible always , it isnumerous to list here all the things that can be done around it , but once you know the control philosophy you can intuitivelyfigure out how to test the logics. Again testing can be done in many ways. One is pure virtual testing, ie you force signalsand test the output , this is is mostly the first stage. Given that you have already throughted the field signals in the firstphase " Plant Instrumentation and control system commissioning " , it should work. Some times client will ask you to test the logicwith the field instruments , they pay you for it so you better keep them happy :).Modifications - If you or the client think that the logic is not performing well, jot down a few modifications necessary to make it workRemarks - Once again boast a success story of a difficult logic or rue over impending modifications : P

By the end of this phase you will again have a lot of papers , assuming 20 main

subsystems and 5 main logic per subsystems , you have around 100 logics to testand tweak. But many are tried and tested logics which you will not need to do anything. Once again i stress the importance of keeping this record , when you dothis for a few sites you will see that you would have covered most of everything you need to see , as always getting by the first few sites is always the difficult task.

Step 4 - Testing and tweaking - This is an iterative process, but i have seen that most of the turbine systems come with a tried and tested code and you seldomtweak anything, its mostly testing to make sure that it works. The conditions is different for boiler control so it it with the turbine auxiliaries. Take into account what the operating and maintenance personnel have to say , at the end ofthe day you need a stellar reputation and it only happens when you keep the clie

nt / operating personnel happy. Over the years i have seen that most of the request for tweaking does not come to modifying the control code but the graphics in the HMI , so make sure that you not only know the control system but also the HMI part of the controller. The final test in tweaking is always a battery of performance tests. This is again platform specific, usually done to test the redundancy and robustness of the controller. you do not have to make a list of battery tests , it will be given to you (much to your displeasure) by your superiors and it is mostly based on the initial contract.

Phase 3 - Optional , always recommended and usually mandatory "End of Commissioning party "!!! where booze flows in rivers but always ends with you getting home for a good rest but still contemplating weather "l63p21%$#" works ;). sigh..

SO that brings to an end of a crash course in commissioning a turbine control system. hope you guys enjoyed it :)