Turbine Trip and Turbine Water Induction

If there is blockage in the steam or fuel feeding the turbine, or a governor malfunction, other generators on the bus would reverse-power the problem one. Hence trip logic.

If the steam to a turbine is inadequately superheated, there may condensate in it. Water droplets will then impinge on the turbine blades, inducing erosion. Worse yet, if a rivulet of condensed water were to hit some blades, they might break.

(This is a "wet" explanation in lieu of a "dry" textbooky one.)

Thank you Tornado..

additional question: regarding instrumentation and cotrols, how to detect this problem and to control so as to minimize this the effect of this problem?

I am not familiar with all turbine instrumentation options, but in theory I think you want to ensure adequate superheat as the steam is about to enter the turbine. A thermocouple (or other suitable temperature sensor) at that location would make sense. You would monitor the pressure at the boiler, look up the saturated steam temperature to match, and check that the turbine entry temperature was greater than that by some amount such as 50°. (I don't know the exact reserve temperature you need, so this is just for illustration. I also did not account for pressure drop, but that works in your favor as far as superheat goes.)

Thank you very much Tornado for imparting your idea..

There are several reasons for a turbine trip...

A turbine trip, in the sense of a steam-driven turbine generating electricity, could be as simple as just shutting down operation of the turbine, or stopping the flow of steam to the steam chest and reheat sections, providing the turbine has a reheat section. It could also be an emergency-stop function of the turbine to prevent a runaway condition. With the turbine driving a generator, and providing the generator breaker is closed and the unit is online, the generator will actually act as a brake, or speed control of sorts for the turbine. The more load that's put on the generator, the more steam volume you have to flow through the turbine to overcome the generator's resistance. If the generator breaker suddenly opened, the load on the generator would be instantly removed, and so would it's "braking" resistance, allowing the turbine to run overspeed freely. This could be a very bad thing. There are also several other types of trips for several different reasons. You could learn about different ones by googling Protective Relays. There are numbers associated with different types, such as overvoltage, undervoltage, difference in potential, overcurrent, loss of phase... etc...

Water induction could be that the steam is wet, or insufficiently superheated as another poster stated, but most usually what water INDUCTION means is that water is backing up through a steam extraction or even through the steam condenser due to a high "hotwell" level. The hotwell is where the majority of the steam that is used to turn the turbine goes after it gets condensed back into water by being cooled in a condenser.

Extractions are different points along the turbine that have pipes extracting steam from different sections of the turbine to preheat water. Each of these pipes that extract steam have "TWIP" valves, or Turbine Water Induction Protection valves. These valves close in the event of water backing up into the extraction. Usually, water heater levels dictate whether these valves go open or close. A high level will close the TWIP, stopping water from getting into the turbine blades.

Water in the turbine most usually will cause erosion of the blade tips, and efficiency will suffer. Blades can actually get worn to the point where they might break off, and that's something that nobody wants... shrapnel flying around in a 20 foot diameter turbine turning at 3600RPM.

I almost forgot...

There are usually little drip legs, or pot drains, as we call them in our plant, that have level sensors in them. If condensate or water enters the line, whether it be steam feeding the turbine or steam extraction, it will flow to this low point pot drain, and the level switch will see it, and activate the TWIP to close.

Hope I didn't confuse you too bad...

First "water induction": In a steam turbine, unless the turbine is designed to operate with liquid water mixed with the steam, the turbine may be seriously damaged when the dense, liquid water strikes the rotor buckets (blades). It is common to sense liquid water in the steam supply header to the turbine and to trip the turbine when water is present.

Some of the usual ways of sensing conditions that would lead to water induction in a steam turbine are to:

1. Monitor the boiler drum level. If the water level in the boiler is high enough that it could begin to flow into the steam header, a level switch may be used to trip the turbine.

2. Monitor the temperature and pressure in the steam supply line and if the temperature and pressure are such that liquid water may be present, the instruments connected to the turbine trip system will shut down the turbine to prevent water induction.

There are other ways but you can do your own work to find them!

There are some, usually small steam turbines which are capable of running on liquid water but these are typically used where they may be subject to such conditions. Because they may be expected to run on steam with water entrained these turbines are designed to accommodate this condition. Typical applications would be fire water pumps and emergency cooling pumps.

Water induction in gas turbines is typically used to increase power output by spraying a fog or extremely small droplets of water into the air intake of the gas turbine. The liquid water flashes to steam as the air heats in the compressor section and increases the expansion when the air/water is heated by combustion of the fuel. This can gain a substantial power increase for a gas turbine. This is sometimes used to gain extra power on peaking turbines.

Have FUN!
TT3