Water mist system for fire protection of electrical power generators 1

[krisys]

We are going to install water mist type fire protection system for the Gas Turbine Generator (GTG) enclosure. One system for the Gas Turbine enclosure and the other one is for the Power Generator Enclosure.

This is an upgrade project where the existing inergen system will be replaced with water mist system. The replacement is required due to the environmental reason. The inergen is not an environment friendly gas.

Can anyone share your experience on this.

My concern here are the following:
a) The alternator is about 36 years old. Hence whether the winding insulation is suitable for such exposure of mist?
b) The starting system may get damaged
c) There is a lube oil system emergency pump, operated with DC supply from battery
d) In case there is an accidental release of water mist on the running generator, what will be the risk?
e) In case there is a water deluge instead of water mist (due to some unknown reasons) on the running generator, what will be the risk?

Your input is appreciated.

 

[edison123]

Hydro electric generators have had water for fire extinguishing for decades. Fire is a bigger destroyer than water.

And yes, accidental water discharges have been known to happen but they have not destroyed the windings as far as I know. As long as the system shuts down when the discharge happens. At worst, the generator windings might require a dry out.

Muthu

http://www.edison.co.in

 

[EdStainless]

I have never hear of a mist system resulting in flooding.
I have seen enclosed rooms after a system test and there are not even puddles on the floor.
Don't go with the low bidder on this.
Use high purity water (keeps nozzles clean and minimized residue)

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P.E. Metallurgy, Plymouth Tube

 

[krisys]

edison123,
Water deluge is different from water mist system. Water mist system is the release of atomized water particles. It shall be sprayed at high pressure at certain conditions to form the cloud. This atomized water particles forms a cloud in the area, thus extinguishing the fire. As other systems such as CO2, Halon etc. are found to be harming the environment and hence the water mist system is getting preference.

EdStainless,
Your input is truly encouraging me to go for the water mist system for my old alternators. But do you have any experience of using it for such installations?

Any one for that matter.

 

[edison123]

Mist or spray, I don't see the difference in terms of affecting the winding insulation.

Muthu

http://www.edison.co.in

 

[EdStainless]

I have seen them used, but it wasn't my plant. The atomized water has no drops, it is a mist.
If it is operated correctly there is no residual water just a very humid room.
The electronics that I saw being protected also had provision for inert gas (nitrogen) purge, the gas was to exclude oxygen while the mist was to remove the heat.

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P.E. Metallurgy, Plymouth Tube

 

[catserveng]

ABB a few years ago had a paper dealing directly with this issue, but I can't find the copy i had, here is a link to one article on FWS i did have, and while it doesn't directly deal with your question as I remember some of the resource articles did.

http://www.nist.gov/el/fire_research/upload/R0000243.pdf

This article compares some of the available technologies,

http://www.powermag.com/fire-protection-options-for-air-cooled-hydroelectric-generators/?pagenum=2

for Hydro generators and seems to do a pretty good job in do a fair assesment.

Hope that helps, MikeL.

 

[lukin1977]

I was always told that inergen system is environmentally friendly and that it was specially developed to replace Halomethane

 

[dogzzz]

We are going to install water mist type fire protection system for the Gas Turbine Generator (GTG) enclosure. One system for the Gas Turbine enclosure and the other one is for the Power Generator Enclosure.

This is an upgrade project where the existing inergen system will be replaced with water mist system.
Normally in offshore projects , water mist is required irrespective of inergen .

The replacement is required due to the environmental reason. The inergen is not an environment friendly gas.
Well more then environment it is not good for human safety

Can anyone share your experience on this.

My concern here are the following:
a) The alternator is about 36 years old. Hence whether the winding insulation is suitable for such exposure of mist?
[highlight #EF2929]Well , from my experience , winding insulation will be OK , after using water mist , if the insulation test shows low insulation then dry the windings till
it get good insulation resistance.

Secondly there will be some big fire , if water mist is getting used , so anyway there will be some damage done to your turbine.
Also , I hope you are using automatic release of water mist based on voting of smoke detectors , to make sure that water mist releases due to a real cause.[/highlight]
b) The starting system may get damaged
buty be or may not be , it need to be inspected .
c) There is a lube oil system emergency pump, operated with DC supply from battery
d) In case there is an accidental release of water mist on the running generator, what will be the risk?
It cannot happen because water mist system is energized based on smoke detector voting and not on one detector activation. Perhaps lets say it happens that water mist is released , in this case also , water mist once activated gives a signal to shut down Turbine - Generator.
It will make your windings wet , and you need to dry them.
In case T-G dont stops , then you can end up having some serious damage to your generator , like a 3 phase short circuit because of the possibility of the
moisture getting into generator terminal box .

e) In case there is a water deluge instead of water mist (due to some unknown reasons) on the running generator, what will be the risk?
same as told in (d)

Your input is appreciated.

 

[prc]

Does any one has experience of using this water mist system for oil filled transformer fire protection? Will it be effective with burning transformer oil?

 

[dogzzz]

Hello PRC
Yes it will be effetive ,much better then gaseous suppression system.
For a transformer ranging 50 to 60 MVA , roughly weighing 500 to 600 tonns , if undergoes a fault like short circuit , will result in core tempreatures rising upto 500 to 600 degree cecius.
At these tempreatures the core and the oil is a potential source of fire.
Water mist shall be able to extinguish the initial fire but the problem is fire reignites or starts again after initial quinching.
Thus a DISCHARGE TIME is calculated for a water mist system , so that the fire do not gets reignited.
This discharge time makes sure that core is cooled enough.
The discharge time is of the order of few hours for above mentioned transformer.
Thanks.

 

[krisys]

prc (Electrical)
For the transformer of 50MVA size, water mist system may not be that effective. Normally fire deluge system is the industry standard.

dogzzz (Electrical)
Water mist protection for alternator fire suppression:- who will stand guarantee for the alternator winding?
Silverline is that the alternator winding may not be open type. It may have some enclosure. Check what is the IP rating of the enclosure. Even if the alternator is splash proof, water mist system should be fine. The water mist will not be condensed when there is a fire. In the event of some condensation, it would settle down not move up.
So in a nutshell is debatable.