STEAM TURBINE ELECTROHYDRULIC TRIP VALVE 1

[alroum]

our plant is 100 mw steam turbine, h .pressure plus low pressure turbine without , some times turbine trip valve partially close during normal operation, trip valve is electohydrulic (DEH) SYSTEM, does any one encounter something like this before?

 

[byrdj]

There can be many possibilities as why this is happening. to determine a possible cause and repair some more information would be needed>

First is this Trip Valve (stop valve) solenoild or servo operated. If Solenoild, the DEH demanded valve's position will be closed, open (or test). If servo, then the DEH will have a position control loop. the possible failure modes for the servo operated will include the calibration and operation of the DEH, the position control loop could be demanding the valve to go closed.

Next, what % closed is the valve going and is it repeatable. If there is only only trip (stop) valve, then the test for it may utilizie a mid stroke drain port to only allow partial test closure Is there some regularity to when closure and reopenig occur. for example, does increase steam pressure cause closure and reduction of steam pressure allow reoping.

Is there any other symptoms like increase hydrulic pump running current, indicating increase flow. is the tubing to the valve indicating possible increase flow as noticed in vibration, noise or temperture

 

[alroum]

Well, its solenoid operated, this incident happened many times in two similar units, stop valve opening fell to 30% and this behavior coincidence with load rising.

 

[alroum]

actually no way stop valve would open until unit trip on drum level very low.

 

[byrdj]

By being solenoild greatly reduces the probability the DCS is the problem.

does the "valve test" fully close the trip valve or does it only go to 30%. IF So, could it be something with the test solenoild.

If the valve is closing as steam pressure increases, then need to look at the valve design to determine the stem "blow out" forces and conpare to the actuator forces. If a weak actuator, the problem could be internal leakage and full pressure not being devolped under the piston. another could be a bad solenoild where the spool is not going full open. then there could be debri blocking the feed port.

Can you post a scan of the trip valve drawing and the control diagram to show the hydrualic logic.

 

[alroum]

pls find attached file

 

[byrdj]

unable to open file

 

[alroum]

thank you byrdj >>>
now test selonid is dismanteled ..
seem you are very experianceed, if you have any case study relating steam turbine power plant i wish to send it over to me @ [COLOR=]eng.ahmed00@gmail.com[/color]

 

[byrdj]

My turbine specific knowlegde is limited to older GE LSTG and a little for GE MDT & MSTG.
However with drawings, I can usually figure things out.

What type of steam turbine do you have?

If possible, re upload the files you attempted to in the prevous post. that file is not acesable

 

[alroum]

EH SYSTEM

 

[byrdj]

I am able to view the "control diagram" for your HTC steam turbine. this drawing is differrent to me. (also think there is error for TV)
the things I noticed is that
1)the unit has only one TV so its online test can not fully close. I do not see any hydrualic arrangement that prevents the solinoild from fully closing the valve. therefore the test solinold must be interrupted by electronics.
2) the drawing does not show an arrangement that would open the TV. I will assume that the connection providing opening fluid would be on the left side of the actuator and connect to the supply line going down, after the orifice. this would make the arrangemnt be a continous orificed flow into the actuator, when the dump valve is closed, the fluid builds up and opens the TV. the "test" solinold drains the oil supplied to the actuator for the TV to close
3) there is a manual isolition valve in the supply, just upstream of the orifice. Is it possible this valve is throttled and reducing the supply fluid flow?
4) there appears to be a manual activation of the dump valve. Is that actual?

Now that I have some ideal of your system, the problem needs to be better defined.
So far I heard the TV drops from 100% to 30% for no reason.
Is there a loss of load when this happens?
Has the actual movement of the TV been observed or is this only from indication?
Does it reopen on its own or is there some action taken?

 

[alroum]

yes, there is one trip valve and it does close, load drop, TV cant fully open again untill unit trip on drum levl low
some times also when we are going to steam to set, trip valve only open 30% and failed to close, our practice is to swith test selonid supply off and then valve open 100% then supply on and tv drop to 29% open and repeat this untill trip valve fully closed then it can be open fully.

 

[byrdj]

yes, there is one trip valve and it does close, load drop, TV cant fully open again untill unit trip on drum levl low
Normally a TV can not fully open unless the GV are full closed. the force of the actuator can not over come full steam pressure up stream and vacuum down stream. If trying to reopen with GV open, the internal TV has an equilizing valve (sometimes call bypass) that is small seat diameter than main disk that will allow the steam to open about 30%. then when it tries to lift the main TV disk, the steam pressure above is too great. By closing the GV, the pressure below the disk increases so the delta accross the disk is reduced and the TV opens 100%


If the turbine has only one TV, the online test should only partially close, about to 80% open position. From your "control diagram", this must be determined by the electronics. I would think a limit switch that interupts current to the test solenold.

Is the "control diagram" missing a connection fron the high pressure fluid black line to the TV actuator?

some times also when we are going to steam to set, trip valve only open 30% and failed to close, our practice is to swith test selonid supply off and then valve open 100% then supply on and tv drop to 29% open and repeat this untill trip valve fully closed then it can be open fully.
Sorry, but I can not understand this.

 

[alroum]

sorry,sometimes when we about to open tv to run up turbine ~Steam admission-, tv open only 30 percent and stop, and failed to close even if turbine trip push button activiated, my college used to switch test selonid supply off then tv goes full open, when thy switch supply on again tv drop to 29 percent open, repeating this switching off and on untill trip valve fully closed, then next time when tv is openned it does open fully

 

[byrdj]

sorry,sometimes when we about to open tv to run up turbine ~Steam admission-, tv open only 30 percent and stop, and failed to close even if turbine trip push button activiated, my college used to switch test selonid supply off then tv goes full open,
"switch test solenoid supply off"--does this mean electrical power off? If so, I don't understand why the test solenoid would be energized. from the way I understand the drawing, if the test solenoid is energized, the TV should close. So when the electrical power is swithed off, the valve goes open.
when thy switch supply on again tv drop to 29 percent open,
this agrees that when swtich on, the TV wants to close.
repeating this switching off and on untill trip valve fully closed,
first thoughts is there is mechanical binding in the TV
then next time when tv is openned it does open fully

I have to leave now, so it will be latter tonight before I can add any more. I want to consider what could possibly going on with orifices
Attached is how I think the hydrualics for TV work.