what can a gas turbine to short down before it expected time?


Sorry; your question is not clear.

Are you trying to ask: "What can cause a gas turbine to shut down unexpectedly?"

It's a pretty well-followed standard in GE-design heavy duty gas turbine control systems that EVERY SINGLE condition that causes a turbine to trip (meaning the fuel flow is immediately stopped because of some emergency condition such as high-high vibration or low-low lubricating oil pressure) has a Process Alarm message associated with it. So, by looking at the Alarm display and/or Alarm log print-out or the Trip Display or Trip History Display, or even the Trip Display on the HMI--it should be possible to determine what condition resulted in the trip. A turbine trip condition results in the immediate shut-off of fuel flow to the turbine combustors, and that results in an opening of the generator breaker (usually on reverse power) and a coast down to zero speed (cooldown operation). It's used to try to protect the turbine from excessive damage when serious conditions (which should have also been alarmed to the operator) were allowed to continue and either existing for some period of time or became worse.

Another possible question you might be trying to ask is: "What can cause a gas turbine to shut down without an operator initiating the shut down?"

In some cases, there are conditions which are programmed to act as though the turbine has been told to perform an orderly shut down by an operator--these are usually called 'automatic shutdowns.' Some typical reasons for automatic shutdowns are high-high turbine inlet air filter differential pressure or loss of exhaust frame cooling blower fans. These cause the unit to unload (reduce fuel flow and power output) in a controlled, orderly manner, resulting in an opening of the generator breaker and a fired shutdown to zero speed (cooldown operation). These automatic shutdown conditions, too, should have dedicated, specific Process Alarm messages to indicate the reason for the automatic shutdown.

Finally, there are conditions which sometimes result in what are termined "runbacks." A runback is when the unit fuel flow-rate and power output (load) are automatically reduced in an orderly fashion to some low load value and the unit is prevented from being re-loaded again until the alarm condition is resolved. As with the other two scenarios above, there is almost always a dedicated, specific alarm to alert the operator to what is causing the automatic runback.

It should be clear from the above descriptions: Alarm lists are very, Very, VERY important to the proper operation and understanding of gas turbines. The programmers of turbine control systems have standard practices they try to follow to help operators understand when an impending shut down is about to occur by annunciating Process Alarms, and then when the shut down does occur the time (and date) the shut down did occur and the specific reason for the shut down. If the Alarm Logger (Printer) is not working at your site--IT SHOULD BE!!! And, operators, their supervisors and plant management and controls technicians--even mechanical personnel--should ALL be capable of reviewing Alarm Lists (Printouts) to determine what caused a trip or shutdown. Sometimes, it's not the easiest thing in the world to do--but it's also not impossible and MANY people do eventually learn how to do it. Alarm Logs (or Lists, or Printouts) used in conjunction with Trip Displays and Trip History displays can almost always be used to indicate why and when a unit tripped. Just because the one condition which caused the trip isn't printed in red ink with yellow arrows pointing to it doesn't mean it can't found on the list (log; printout).

Hope this helps!!!

If you were trying to ask something different--my apologies for not understanding. Please try to clarify your request and we'll do our best to try to answer concisely and promptly.
Thanks for your concern sir @ CSA
what i meant is that what can cause a gas turbine when shutting down it will be faster then normal time it use too take like before, its 10 mins mow is using 5 mins. which is more faster than before.

What time are you referring to--the time from Base Load to generator breaker opening, or the time from generator breaker opening to zero speed (cooldown operation)?

The time from Base Load to generator breaker opening is a function of a Control Constant--it's a rate that controls how fast the TNR (Turbine Speed Reference) is reduced which controls how fast load is reduced.

The time from generator breaker opening is a function of how quickly FSR is reduced, and to a certain extent, when loss of flame is detected in any combustor with a flame detector during the deceleration from FSNL (Full Speed-No Load (generator breaker opening)). The rate at which FSR is reduced during a normal, fired shutdown is a function of a couple of Control Constants. However, if flame is lost in any combustor with a flame detector during a fired shutdown the Mark* shuts off the flow of fuel to all combustors which can cause the time to decelerate to zero speed (cooldown operation) to be slightly reduced.

I should note that the Control Constant that controls the rate at which TNR is reduced during a shutdown from Base Load is ALSO the same Control Constant and rate at which the unit is automatically loaded and unloaded when using Pre-Selected Load Control, or when selecting Base Load any time after synchronization. So, changing that value to try to decrease the time to unload will also affect the time to load--increasing the loading rate.

Similarly, the way GE wrote the programming for shutdown after generator breaker opening, changing one or both of the Control Constants to decrease the time from generator breaker opening to zero speed (cooldown operation) will also affect the start-up control timing--and sometimes very negatively.

If you can tell us if you are experiencing problems with shutdown times being irregular, or if you want to find a way to reduce shutdown times (for example, so you can re-start the unit quicker after a trip (instead of waiting for the unit to get to zero speed), we can offer suggestions for troubleshooting or a mechanical solution to the problem of having to wait for zero speed before re-starting the turbine after a trip. (Though, reducing the number and frequency of trips is always the best solution for the problem of having to wait for the unit to reach zero speed before being able to re-start it!)

Anyway, hope this helps! I realize English is probably not your first language, but the more information you can provide in you original post the better the responses will usually be. If you're not familiar with Google Translate, it's a very good tool for translating information. It's not always 100% accurate, but it is pretty darn good at most translations (though, admittedly, some technical terms and topics it doesn't always do well with).