Steam Turbine Stop Valve Testing

Steam Turbine Stop Valve testing. We regularly test our Steam Turbine Emergency S top valve to ensure it does not get stuck open. The question was posed, what if the valve does stick open. How could you safely shut down the turbine? We are developing a procedure for this and an d I am curious if anybody else already has an established procedure for  this problem. If so, please share it. 15 days ago 

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vijay patil, patil, Zeeshan Uddin and 2 others like this You, vijay patil, patil, Zeeshan Uddin and 2 others like this 52 comments• Jump to most recent comments

UdhayakumarUnfollow Follow Udhayakumar  Udhayakumar Venkataraman • As Governing vale can not be 100% shut valve, passing may over speed or  shaft will not come to barring, churning may happen. How to bring down shaft speed down?? will add, all our expert friends may address..if over speed sensor does not operate.. disaster in this ESV does not close but the GV closed fully... 15 days ago• ago• Unlike• Like   

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MaheshUnfollow Follow Mahesh

Mahesh Manoharan • It is usually recommened to open op en the Generator breaker after experiencing reverse  power in case of tripping of the Turbine on any protections or manual shutdown of the Turbine. This is usually called programmed reverse power protection or sequential reverse power protection. Except for any electrical protections the generator breaker will be opened after experiencing reverse power in case of any tripping due to boiler or turbine protections ( except few turbine protections like Diff expansion). This is to ensure that all the locked out steam got exhausted and the TG set is entering into motoring action. This will avoid over speeding of the TG set due to passing of ESV and GV's. 15 days ago• ago• Unlike• Like   

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VictorUnfollow Follow Victor  Victor Buck • Buck • Russel, can you give more info on all turbine steam valves on o n your unit (governor valves, throttle valves, etc.)? Our Westinghouse unit has 2 throttle valves, 6 governor valves and 4 reheat valves (2 stops and 2 intercepts). Although Udhayakumar states that a governor valve cannot be a fully shut valve...that is not the case on our unit. At approximately 10% indicated governor valve position, all steam flow through that valve has stopped. In our situation, if we had any one valve stick open, we would still be able to stop all steam flow and safely shut down the unit. Your situation may be completely different and, withou t knowing your exact valve layout, la yout, it is hard to give a good recommendation. 15 days ago• ago• Unlike• Like   

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AlanUnfollow Follow Alan Alan Manza • If the steam turbine emergency stop valve failed to close during unit tripping or normal shutdown, these are my recommendation: 1) Open the generator circuit breaker manually to isolate from the grid and to protect it from reverse power, although reverse power protection is present. 2.) During opening of  the generator breaker, the steam turbine speed may increase and possibly reaches to its overspeed ove rspeed limit since the emergency stop valve is stucked open. The steam turbine may trip by activating the overspeed protection. 3) Then, try to open the vacuum breaker to aid slowing down of steam turbine.

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 josephUnfollow Follow joseph  joseph hanna • I think we need more details about your system. In our plant: 1. sure there is a reverse power   protection to open the circuit breaker or even manually you can open the breaker but this wil not protect the turbine, it will only protect the generator. 2. there are boiler main steam stop valves which isolate boiler  steam from going to turbine (sure you have to trip the boiler if you want to protect the turbine). Same story we have with reheat inlet outlet from boiler. 13 days ago• Unlike• Like   

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 NareshUnfollow Follow Naresh  Naresh Bansal • Add another similar stop valve if it helps to care of the anxiety meanwhile I am waiting for  the procedure being worked out by your team. 13 days ago• Unlike• Like   

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KONSTANTINOSUnfollow Follow KONSTANTINOS KONSTANTINOS FARMAKIS • 1)if the valve fail to close with the first trip signal it will never close by the overspeed trip protection.

2)the result of the opening of the breaker will be an overspeed without possibility of tripping because the stacked valve. The damage will be very big 3)dont break the vaccum with full steam flow through the steam turbine what im thinking: 1)open the by passes .be carefull for the drum levels. we dont care about the hihi trip level, we already tripped , but for water to the steam turbine 2)open the steam line drains to redure the pressure and flow and to extract water from the steam lines. 3)if there is main isolation valve close it . the drum PSVs will open 4) open the breaker  5) less than 85% speed , with out steam flow break the vaccum. and good luck. 13 days ago• Unlike• Like   

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BobUnfollow Follow Bob Bob Callery • If the steam turbine ESV (emergency stops valv es ) will not close, I recommend Not Opening the Generator Breaker unless you want your steam turbine parts flying into the parking lot! Trip the boiler and close the boiler steam stop valves. As the turbine speed decreases, the generator breaker  will open upon activation of the reverse current relay. This condition ( failure of the ESV ) is one of the most dangerous conditions in a power plant and training and procedures must be in place by the operating crews to understand how to deal with it. 13 days ago• Unlike• Like   

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 josephUnfollow Follow joseph  joseph yarusinski • Your primary steam inlet valves should always be installed in series... - Throttle Valve / Control Valvees - Reheat Stop Valve / Interceptor Valves. The valves should take hydraulic pressure to open, and spring pressure to close. The springs provide a fail-

safe means of closing the valves on loss of hydraulic pressure or electric power. Upon a turbine trip (due to low vacuum, low bearing oil pressure, loss of control oil p ressure, complete loss of load / overspeed trip) all valves should very quickly slam shut. And all valves should seal off 100% of flow. You must test the operation of the valves regularly. If you don't, mineral deposits from the steam may build up along the valve stems and basically cement them in place. This will prevent the valves from closing in a n emergency. Very simply, if the valves do not stop the steam flow very quickly in an emergency, the turbine will be severely damaged. For instance, a steam turbine can accelerate to destructive overspeed in just a few minutes, if the valves don't shut tight. You don 't have time to take any other course of action --- except maybe to trip the boiler as you are running out the control room door to safety. 12 days ago• Unlike• Like   

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Siraj AhmedUnfollow Follow Siraj Ahmed Siraj Ahmed Khushk • Agreed with the comment of Mr. Bob Callery. We may also close the main steam line isolation valves of boiler. Plus some frnds suggested here to open Gen. CB and let the turbine trip on overspeed but if t he turbine Stop valve is stuck, it wont be fully closed and will allow the steam flow. So i totally agree with Mr. Bob Callery 12 days ago• Unlike• Like   

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DaveUnfollow Follow Dave Dave Muller • Hi, not sure of your configuration, but we would also close the control vales at the same time, if these still pass then go further back and close the isolation valves. Cheers.

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hannesUnfollow Follow hannes hannes hedquist • Only by means of control valve closing and boiler isolation valve too. Naturally trip the machine and break vacuum plus bypass valve fully open. 12 days ago• Unlike• Like   

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vijayUnfollow Follow vijay vijay patil • when plant tripped and ESV remain open ..there is chance of overspeeding of turbine ..so immediately close the MSV valve which is in series ofESV ..after that close speeder gear to zero ..then break  condenser vaccuum immediately ..this result turbine coast down within 15 min & come on barring..but sometimes MSV valves are also passing so close  boiler outlet steam valve 12 days ago• Unlike• Like   

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LorneUnfollow Follow Lorne Lorne Kause • If your turbine stop valve sticks open immediate action must be taken to protect your turbine from overspeed distruction as your main means of steam isolation has been lost and as noted governor valves

should not be relied on for isolation as that is not their purpose. Immediate shutdown is required but under  "very" controlled conditions. I would suggest reducing boiler p ressure to the lost allowable operating  pressure and bring the generation down to minimum (mtoring condition)--this will provide indication if the governor valves are providing control at minmum steam flow. At this point it is suggested your turbine can  be tripped. If your unit is provided with boiler stop valves these should be closed as well. 12 days ago• Unlike• Like   

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Jean-PierreUnfollow Follow Jean-Pierre Jean-Pierre Rickli • Hi Russel If the valve sticks open during the test, that means that some concerns may rise about a safe shut-down of the ST in an emergency case. In most Arrangements, you have one ESV in serie with one or more control steam valves. That means that you are still able to run down the ST in a controlled manner by reducing the load and closing the control valves. Possibly, you will have also to reduce the boiler load.and thus the steam data. The ESV gives you confidence, that the ST will be stopped despite any problems with the control valves. If the ESV is stucked, you may be careful while loading down the ST in order to avoid the necessity of an emergency stop. Once the ST is stopped, you can get the ESV problem fixed. The test during Operation gives you the opportunity to have a scheduled shut-down for Fixing the ESV and not be surprised by an emergency case. Hope, it brings some help. 11 days ago• Unlike• Like   

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GidionUnfollow Follow Gidion Gidion Mutanga • This is a serious condition, if ESVs are stuck open, trip the boiler first and close boiler  steam stop valves to stop steam flow to the turbine and open drains, to drain away water. If the circuit

 breaker did not trip on protection as the turbine speed decreases, then open it manually. Time to act is very limited here, it's why I believe tripping the boiler should be the first thing to do. 11 days ago• Unlike• Like   

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FirozeUnfollow Follow Firoze Firoze Kazi • Open the turbine steam bypass valves to the condenser and shut the boiler steam valves. 11 days ago• Unlike• Like   

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KalyanUnfollow Follow Kalyan Kalyan Kumar • Your plant configuration is required for suggesting a solution correctly. If there are multiple  boilers supplying steam to multiple STs through a main steam header, it may become practically impossible to close the boiler main steam valves, if the availability of other STs should not be disturbed. In that case, consolidation of some of the above suggestions can be used to prepare a SOP. 11 days ago• Unlike• Like   

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JoeUnfollow Follow Joe

Joe Moroso • I think reiterating Bob Callery's statement is warranted. The last thing you want to do is open the breaker while still introducing any steam energy into the turbine. Once the energy is expended and you start getting into a reverse current/motoring situation the generator protection system will open the breaker. 10 days ago• Unlike• Like   

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ChuckUnfollow Follow Chuck  Chuck Holm • Typically the governor valves will also close to prevent turbine overspeed. We typically test the stop valve and the governor valves (and reheat/intercept if installed). I haven't worked on a turbine that the governor valves cannot go fully closed. The generator breaker should not be opened unless you see reverse power. If the stop valve and the governor  valves fail to close, keep the generator in service and use another means to isolate the steam. You're doing the right thing by trying to come up with a plan before an event actually occurs. I've actually never heard of all valves failing to close during an emergency when the valves are tested regularly - EXCEPT at a couple of facilities where the trip oil/hydraulic system was modified and when the a trip was required - the oil did not dump off the valves. In these instances the valves test everytime until a real emergency occurred. 10 days ago• Unlike• Like   

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RusselUnfollow Follow Russel Russel Alexander • Its good to see some of the same thoughts we had about this situation. I will describe our turbine setup. We have a steam turbine with a single Emergency Stop valve (ESV) and 4 governing valves. There is a Main stop valve after the Superheater which is manually operated and a small solenoid operated vent valve  between the Main stop valve and the Turbine ESV. The ESV is held open h ydraulically and closes on loss of hydraulic pressure by a spring. All the safety devices i.e. overspeed, emergency stop, trip a solenoid which drops the hydraulic pressure.

So if the ESV does stick open there is no protection of the turbine. So far we have come up with the following steps to safely shut down the turbine. 1. Reduce the firing rate of the boiler  2. Start lowering the load of the turbine 3. Start closing the manual Main stop valve and do not stop until the valve is completely closed. 4. The operator shall trip the boiler fire and will put the MW control at minimum so the governing valves stay closed and do not try to open as the steam pressure drops and the turbine load goes down. 5. As the turbine load starts to drop, open the steam vent solenoid valve when load is at approx 2 MW's 6. As the unit is approaching 0 MW's open the vacuum breaker on the condenser. 7. Allow the load to continue to drop, so the unit goes into a reverse power condition and the breaker trips. 8. At this point the Main stop valve should be closed, the governing valves should be at minimum, the steam vent valve is venting any residual pressure in the steam line and the turbine should be spinning down. 10 days ago• Unlike• Like   

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ChuckUnfollow Follow Chuck  Chuck Holm • Are you certain that the governor valves will stay open when hydraulic fluid is dumped from the stop valve. And if the governor valves actually do stay in service when hydraulic pressure is dumped from the ESV - should they stay open and was a modification made at some point that allowed this to occur. I can't recall ever operating on a turbine that had separate h ydraulic systems for the ESV and the governor  valves and I've worked on a lot. The ESV and governor valves should be supplied by the same hydraulic system. I actually have a steam turbine design engineering manual for Russian made turbines and it also indicates that governor valves and stop valves bei ng tied together in the trip circuit. Just a thought!! 10 days ago• Unlike• Like   

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RanamunimUnfollow Follow Ranamunim

Ranamunim Ranamunim • DO NOT OPEN THE BREAKER, LET THE GENERATOR MOTORING FOR  A WHILE IF EMERGENCY STOP VALVE IS STICKED OR PASSING THEN C LOSE THE MAIN STEAM GATE VALVE. 10 days ago• Unlike• Like   

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RusselUnfollow Follow Russel Russel Alexander • Chuck, you are correct. If the hydraulic pressure is dumped the governor valves will close. What I was referring to was if the control system has a setpoint of 10MW's and we start closing the main stop valve, As the MW's drop off, the control system will respond by opening the gov ernor valves back up to try and bring the load back to 10MW's. My thought is to keep the governor valves closed off as much as possible so that when the breaker opens, the control valves are not wide open to allow what ever steam pressure is left to go through the turbine. But you brought up a good point, somewhere in the procedure should be a point where we trip the hydraulic  pressure also. 10 days ago• Unlike• Like   

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ChuckUnfollow Follow Chuck  Chuck Holm • Very good Russel. If you have reverse power protection and most do these days, the turbine will not overspeed and will give you time to close other valves etc and as the steam supply falls off the load will drop and the generator breaker will open when reverse power is detected. The scary scenarios are loss of lube oil, ex treme high vibration, thrust failure, and differential expansion causing rotating/stationary component contact - just to name a couple. What would be the response for each scenario if the valves failed to close and isolate the turbine properly. Gives me shivers just thinking about it. Fortunately, I do feel that valves failing to close is very rare. 10 days ago• Unlike• Like

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DarrylUnfollow Follow Darryl Darryl Vincent • If you have an EHC system, you can isolate and drain the EHC fluid off of the servo valves for the govenor valves.This would allow them to go closed. 10 days ago• Unlike• Like   

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BarbaraUnfollow Follow Barbara Barbara Rousseau • we hv a monitoring system rf+smart sensors which gives an alarm...pls visit www.dynamicglobalrf.com 10 days ago• Unlike• Like   

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dariushUnfollow Follow dariush dariush zarei • dont worry my dear as like m y dears said its enough that you close the isolation valve (its down ester than esv ) it will be decrease the steam flow to zero and and unit goes to bypass and turbine speed will be decrease without any risk  attention: you cant open the gen.breaker before your steam flow decrease to zero 10 days ago• Unlike• Like

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JohnUnfollow Follow John John Melon • Many MSV's are motor operated and I would like to raise the safety question regarding the intent to send an Operator up to close manual ones in this situation (i.e. high loads/flows). While we all _know_ to close this valve very slowly, I could imagine there may be a sense of urgency during this scenario and some operators would be more likely to close it "less slowly" than others. I'm not sure I would direct anyone to that location as part of my protocol if I were faced with similar circumstances. Mw Control could more expediently be set to "0", or "2" as your suggest, to more completely close the control/throttle valves instead of holding the ramp at a setpoint of "10". If this is a controlled shutdown without an ESV, why open the vacuum break any earlier that usual? I agree that you will definitely slow the machine more quickly. I'm not sure you will like the results. I also don't know that given the implied state of affairs (failed ESV) that I would choose this time to test either my overspeed or my reverse power protection. We do not know that the turbine/genset "will not" overspeed, we only know that it "should not". Those systems are in place for protection if other processes go wrong. Things have a way of happening at the worst possible moments and surprises in this business are generally bad. Expect to maintain full manual control all the way down and write the procedure accordingly. 9 days ago• Unlike• Like   

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BrandiUnfollow Follow Brandi Brandi Irwin • If the valve is stuck there maybe there could be contamination your fluid that can damage the inside of the actuators. We specialize in the repair of hydraulic servo valves, cylinders, actuators (intercept, governor, & throttle valves and main stop actuators) and spring cans. If time constraints are issues we offer a variety of expedite services to meet your outage schedule. We also are a stocking supplier of new and remanufactured valves. We also have EHC Capital Spares /complete units for optimal turnaround requirements. If you could like use to take a look at your units please contact me can I will be happ y to send you a quote. 9 days ago• Unlike• Like

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hannesUnfollow Follow hannes hannes hedquist • Partly agree with one IMPORTANT exception. Close turbine control valve/-s should be first priority IMMEDIATELY ! 8 days ago• Unlike• Like   

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MubashirUnfollow Follow Mubashir  Mubashir Nadeem • I totally agree with Mr. Bob Callery as I witnessed the overspeeding of 66 MW GE turbine on opening of generator breaker as the turbine governor valves stuck and it fails to trip on overspeed  protection . 8 days ago• Unlike• Like   

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VictorUnfollow Follow Victor  Victor Buck • Personally, I would not take a chance on waiting for the Reverse Power Rela y to trip the unit in this situation. I would reduce load to minimum and then trip the turbine so that the governor valves close. But that's just me ;-P 8 days ago• Unlike• Like

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dariushUnfollow Follow dariush dariush zarei • excuse me my dears how can it possible ( trip the unit) when our valves have problem to close if the overspeeding act and open the gen.breaker turbine speed will be increase suddenly and it will be damage because valves were opened the best way is : DELETE THE STEAM FLOW 7 days ago• Unlike• Like   

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dariushUnfollow Follow dariush dariush zarei • yea, i am agree with Mr. Bob Callery but even it dont need to trip the boiler you can close the isolation valve that it is before the esv 7 days ago• Unlike• Like   

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ClintUnfollow Follow Clint Clint Anderson • Opening your generator main breaker is the last thing you want to do in any situation where your steam supply to the turbine cannot be positively shut off. It is the electrical load that is preventing your  turbine and generator from over-speeding. Without the electrical load it does not take much steam energy to “spin-up” a turbine to a catastrophic speed. (See Bob Callerys’ statement “parts in the park ing lot”) Your   best approach is to trip your boiler and close your boiler main steam stop and wait for reverse power.

The whole reason for regularly testing your emergenc y shut off valve is to identify when it is no t closing so that you can take proactive measures to repair it. All of the advice abou t what to do in order to safely shut down your turbine when the ESV fails will not help you during an instantaneous electrical trip during which your unit CB opens immediately. In this case you run the risk of admitting steam to your turbine after the electrical load has been removed. If you bleed off steam from certain stages of your turbine to provide heating to feed water heaters or the deaerator part of your regular testing should ensure that the non-return valves to these vessels will also shut during a trip as these vessels can supply enough energy to your turbine to cause over-speed damage. 7 days ago• Unlike• Like   

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hannesUnfollow Follow hannes hannes hedquist • Dear all. You have many comments that are well grounded in field experience. I respect that. I must still stress though that closing the turbine control valve is prio. 1 as that valve will bemuch faster reacting the the boiler shutoff valve. Of course also opening the generator field b reaker will surely spell disaster as there will be nothing stopping the ST from over-reving uncontrollably with disasterous over speed as r esult. 7 days ago• Unlike• Like   

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 janannathUnfollow Follow janannath  janannath santhosh kumar • in this case, we have to reduce the load in sliding pressure mode to minimum, open the HP bypss lower the inlet main steam pressure then open the GCB. by this we can avoid the over  speed. 6 days ago• Unlike• Like  

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PeterUnfollow Follow Peter  Peter Homan • Hello Russel, we could provide you our valves to your turbine. Since 2005 we had exported quite a lot valves to qute a few projects for power plants and water treatment. 6 days ago• Unlike• Like   

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AdelUnfollow Follow Adel Adel Singab • first decrease load of the boiler and decrease boiler pressure too to the minimum oper ating values, then shut boiler stop valve and let the steam turbine trip by reverse power protection, never trip the  boiler because it may trip the turbine too, never open GCB 6 days ago• Unlike• Like   

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 bonaUnfollow Follow bona  bona rajagukguk • I will try to answer that problem. Should we split the problem in two events. 1 : when the generator is still in the grid. 2 generators are separated from the grid. Under these conditions the position of  the unit in a state boiler follow. We can reduce the amount of fuel in the boiler until the pressure is minimum and led steam to Condenser throug HP Turbine bypass. After that do the MFT (master Fuel Trip ) of Boiler  6 days ago• Unlike• Like

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TomUnfollow Follow Tom Tom McCandless • I had the TTV (Trip Throttle Valve) stick open after I pushed the trip button on the Woodward 505 govenor. The floor operator had to close the manual steam stop isolation vavle, and then trip the generator breaker  locally, very scarey situation. We do the same as Russel for testing weekly now. The valves get stuck due to the operator opening the valve all the way , but they don't back seat the valve 1/2 turn to ensure the valve is not stuck and locked open position. Also we bungee the TTV hand wheel so it does not vibrate closed, this has happened also. 5 days ago• Unlike• Like   

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JonnyUnfollow Follow Jonny Jonny ma • first push off the emergency trip usually at upp er trip controller and close all steam supply valve to turbine this is the safety way to make the turbine not in overspeed conditions,wait till turbine totaly stop check and do cleaning for main stop.valve and selenoid valve control. 5 days ago• Unlike• Like   

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JimUnfollow Follow Jim

Jim Bagley • Bob Callery is 100% correct. You need to take the steam of of the unit by other means. This means shutting down the steam source. If you open the generator breaker without getting the steam off of the unit and allowing the generator breaker to open on reverse current due to the decreasing steam pressure then the unit will over speed and the unit will be destroyed. It takes very little steam to send a steam turbine to self  destruct speed. 3 days ago• Unlike• Like   

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WayneUnfollow Follow Wayne Wayne Karberg • NEVER -NEVER-NEVER manually open the generator breaker upon a plant upset that trips the turbine UNTIL YOU ARE ABSOLUTELY SURE THAT THE G ENERATOR LOAD IS BELOW ZERO (motoring). IF THERE IS STILL A POSITIVE LOAD BEING GENERATED, YOU MUST STOP STEAM FLOW BY ANOTHER MEANS, SUCH AS CLOSING A BOILER ISOLATION VALVE (which can take a long time) and OPENING POWER OPERATED BOILER RELIEF VALVES. That said, if the generator experiences an electrical problem that opens the generator breaker while under  load, AND you still have steam flow through the turbine for any variety of reasons, you will experience a "prompt overspeed event" that can be unpredicable, but is typically disasterous. That is the reason you MUST have confidence that your MSV's or other Tripping Style valves are free to operate. Period. Periodic On-line valve freedom testing is the best way to assure this.  Now, what happens if the tripping valve internal assembly becomes "disassembled" while in service??? 2 days ago• Unlike• Like   

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kiranUnfollow Follow kiran kiran lenka • ESV is not 100% closing. It has some passing.Trip the generator.Isolate the steam inlet isolation valve to turbine as soon as possible.Cut vacuum by opening vacuum breaker valve. 2 days ago• Unlike• Like

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WayneUnfollow Follow Wayne Wayne Karberg • NO, NO, NO! NEVER trip the generator breaker until you are POSITIVE the steam f low is below a level that motors the generator!!!! A VERY b ad response above!!!! 2 days ago• Unlike• Like   

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FirozeUnfollow Follow Firoze Firoze Kazi • 1. Open the steam turbine bypass valves. 2. Shut the steam isolation valves upstream of the steam turbine and at the steam generator. 3. Wait for low forward power relay to pick up. 4.Open the grid circuit breaker. 2 days ago• Unlike• Like   

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ScottUnfollow Follow Scott Scott Long • Russell, I might consider automating the manual Main Steam Stop Valve. This would eliminate the need to put an operator in a potentially unsafe situation, and also ensure that the rate of closing is consistent. It also frees up an operator to address various other checklist items in this situation.

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hannesUnfollow Follow hannes hannes hedquist • It is true that ESV may not be 100% closing, however according to all (to me known) OEM's that passing should not be able to keep the turbine on load, - maximum is a medium speed of idle roll of maximum 30-70 % of full rpm. 1 day ago• Unlike• Like   

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Anacleto JrUnfollow Follow Anacleto Jr  Anacleto Jr Adviento • One good SOP (we implemented in a large geothermal steam power plant) to avoid stuck up of ESVs is to have a routine Stem Freedom Test that would ensure both the mechanical & control systems are working well. Of course depending on the design if you have 2 steam supply inlet to the turbine that this is possible without any load curtailment. A b ypass line with a control valve & isolation valves across the ESV, equipped with a controller can be considered when doing a SFT with a single steam inlet to the turbine. This scheme reduces the potential for emergency stop valve sticking up and turbine over speed when a trip signal occur. 1 day ago• Unlike• Like   

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vijayUnfollow Follow vijay vijay patil • At first lower the firing rate of boiler &cut of the rate o f fuel to lower down the steam drum pr. also simultenously lower the load upto 15 MW by turbine master manual control ..then bypass the TT/BTswitch ..then trip the boiler ..but turbine may not trip due to bypass TT/BT interlock..then close the MSV valves (L/R) simultenously lowering steam input to turbine .. after some time generator will trip on reverse power relay..causing turbine trip after that ...& due to less steam input turbine will not overspeed ...after that close speeder gear to zero to ensured the control valve shut off..so no steam will go in turbine &turbine speed falls ..after that break the vacuum ..&it will assist to stop the turbine towards zero speed then we put the rotor on barring ....& we protect the turbine from destructing..thanks 54 minutes ago

 Naresh Bansal • ESV stuck up. Speciality of ESV is fast closure, time is in micro seconds, which no other valve can provide.Control valves time to cut off steam is much higher than ESV's & may be in seconds. In case of class 'A' tripping,Transient speed rise in normal cond itions is expected to be 7 to 9% of the rated speed rise i.e opening of GCB. So in this case,wish turbine is tripped on reverse p ower protection only. Efforts to reduce the level of energy in front of turbine control valves are needed or must.Opening of HP/LP  byepass will help. Vaccum breaker can not be opened till turbine steam admission valves are open. Must thank all for an excellent discussion & cont ribution. 2 hours ago• Unlike• Like   

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