A Problem in Governing Valve, Seems Like a Leakage in There , But It is Not

Are you by chance running the turbine uncoupled?

Before you spend any more money blindly, why not call in a Mitsubishi field tech to tell you what the problem is?

How do you know there is no leakage when the evidence (a turbine that speeds up by itself?) points to the fact that steam IS getting into the turbine. You need to do a leakdown test on all your steam valves, an emergency stop valve means just that, no steam gets through. Looking at the disc(s) isn't enough, you have to look at the seals, mating surfaces, packing, etc. for the source of the leak(s).

Yes we running uncoupled We have remove emergency stop valve and check it. There is nothing broken there

First of all did you Set the Governor valve link to Governor properly. There should be a procedure in your manual on how to set the Governing valve. The minimum position of Governor should match with the minimum position of Governor valve.

There should be a drain valve in your steam chest, just keep it open and try to play with it to manually control the speed and also you must be admitting in steam only through the warm up valve and not through the main steam inlet valve. As the Turbine is decoupled which must be the case for OST, there is no load on turbine and hence it can always speed up. Keeping the Steam chest drain valve open will help in slower acceleration of the Turbine and can help in regulating the speed much better.

All the best.

All is set in minimum position Look. It is my first time we did ost in steam condensing turbine in no load. But in other case we have many times did ost in no load position in backpress turbine type. This turbine is did not like that. The turbine is Running in minimum governor speed even inlet steam Valve in full opened position. It is not same like steam condensing turbine which just 4kg/cm2 and the speed increase Untill the turbine trip. I wonder if steam condensing turbine can not doing ost in no load like backpress turbine right ?

Whatever be the turbine type, in order to prevent Turbine Rotor running off the best practise is to Admit steam only through the warm up valve only so that the Total steam supplied to the Turbine is just sufficient enough to roll the rotor during a solo run. In your case the Turbine Rotor may be having very low resistance that it can spin even with a low steam flow rates. Your Governor valve minimum position is set to cater to the need of coupled run and not solorun. This opening may still be too high for solorun. In such a scenario our practice is to admit steam only through the warm up valve which normally will be 3/4" dia valve. This will make sure that you do not supply higher steam flow than is absolutely needed and can avoid run away situations. Just imagine what will happen if your OST mechanism fails. Your test is now to confirm whether it is working or not. So you have to be very careful in how much steam you are supplying in and that too it should be in a controlled manner. If the flow through warm up valve is not enough then we can crack open the main valve just to add that extra amount of steam required.

Hope I have shed enough light in to what I think is the issue. All the best.

Unless you have the magical perpetual motion machine, steam is getting to the

turbine somehow.

A visual inspection of the valves does not give much useful information.

Apply air and/or steam pressure and test the valves individually.

The bad valve(s) will show up.

An infrared scanner may be helpful in some cases.

Be analytical and use common sense.

Their seems to be problem with your throttle valve/governor valve which is not closing accordingly after achieving rated speed. You can try by starting turbine manually and check for same is happening now also. You have not mentioned at what speed turbine is tripping. May be malfunctioning of trip device. Check that also.

Thanks to all of you You are open my mind I take a decision. Start ost in coupled position with minimum load Then the turbine is not over speed again. The turbin speed still in minimum governing speed and not like was

The turbine is trip in 4500rpm. It is same with its design

Then i start the turbine in full load and everything is fine