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Posted By zkhan1978
Dear All,
Three Diesel Generators (110kv) were connected with an External Diesel Tank (metal tank) through armored hoses (stainles steel)coated with plastic. After setting up all electrical connections, Generators started. Suddenly one DG stopped. Again it started by operator. After 10 minutes it was found that all external fuel lines (armoured hoses) connected to Diesel tank, caught fire with smoke.
Pleaese explain any one, what may be the possible causes of fire.
Is it due to flow of current on armored hoses? because may be DG not grounded properly or wrong connection of wire?
thanks!
zabiullah
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Posted By jom
Dear Z,
Interesting incident,Z.
Was there any indication of loose joints leading to fuel leaks?
What was actually on fire - the plastic coating or diesel?
John.
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Posted By zkhan1978
Dear John,
Fire was on the hoses, pvc jacket melted.DG were running directaly from external diesel tank.Hoses were of metal and covered with Plastic (PVC) There was no any disel leakage.
since last two months, i am trying to find out the reason.
Zabiullah
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Posted By DPK
It is difficult to give an exact cause of incident with out all the facts and undertaking a incident investigation. But you ask for opinions and mine is an electrical fault would be my first point of call, however with that said stainless steel is not a great conductor of electricity due to the hard composite of the metal (soft metals conduct better than hard metals)so it would have been a significant electrical leakage to melt the plastic sheath.
Other areas to consider would be heat conduction down the fuel line, radiated heat from the generator exhaust etc.
I know its not much help as my answer is purely speculation and the cause may be none of the above, but just trying to give you other options to consider.
Has the incident occured again?
DPK
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Posted By Jay Joshi
There could be several factors, the most likely being the conduction of excess heat (rather than electricity) of the generator to the hoses.
Some points to consider:-
Did the engine overheat? Modern ones have temperature cut-offs,but did the cut-off work??
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Posted By jom
Zabiullah,
Can I clarify something? You say the fuel lines are armored hoses and they are stainless steel coated with plastic.
I'm confused. Hoses are flexible, and steel tubes will be rigid and not usually called hoses, I think.
Are they actually flexible fuel lines? These are plastic tubes encased in st/st or Hastelloy braiding.
Since you say the PVC coating burned, then it seems that the plasctic is on the outside. Can you tell us why stainless steel tubing would need plasctic coating? I know that's not solving your question, but I'm interested.
John.
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Posted By Peter How
Dear zabiullah
I believe you have correctly answered your own question.
If the PVC covering of the conductive (metal braided) diesel fuel lines is melting, then this indicates the fuel lines are getting hot.
Electrical engineers spend a lot of their time dealing with stray earth leakage currents.
The 3 DG will be generating electrical power, they are usually 3 phase (415v) with a netural (return) and an earth conductor. There are usually out of balance currents that will cause neutral current flow. Most networks have the neutral connected to earth at the generator (or transformer) as well. Voltage drop due to current flow along cables (Ohms law V=IR)will cause different voltages to be on the earth cables and the neutral cables across each of the generators. Unless there are good , solid earth rods driven into the ground and connected together and to each DG, then these earth or neutral currents are trying to flow along the fuel lines via the tank and making them hot. Currents may be many amps (say 100a).
How was the problem solved?. It should have happened every time the DGs were run on load, or have the loads been balanced better?
regards Peter
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Posted By Paul T9
Just a guess here, hot climate or desert, metal pipes covered to prevent damage from sand and wind?
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Posted By Eric Taylor
I'd go with the stray current theory. Had a similar experience when trying to weld part of a rally car. Didn't realise the part was supported in non-metallic bearings. Earth was trying to run down the braided brake line. Took a good few goes and holding the governor open on the generator for the welder before we eventually managed to force enough current down the hose. Man did it smoke, but it didn't leak.get Find out from the manual or manufacturer what the earthing requirements are and get an electrician to check regularly to prevent it happening again
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