Voltage too high 4

[roemer]

Hi everybody,
After installing modern lighting, in a school, the lamps flickered all the time, I measured the voltages:
L1=230V, L2=260V, L3=230V
Load is basically evenly distributed over the phases. In the Substation the transformer occasionally makes a bubbling sound suggesting gases rising in the oil.Any ideas as to possible causes of the over-voltage?

 

[k2panman]

Sounds like the input to the transformer could be unbalanced. 260V is too hi - 252V is what you should see max.

I don't think overvoltage would cause flicker though. And the bubbling transformer sounds like a third problem.

K2ofKeyLargo

 

[waross]

A primary turn to turn short would cause a higher voltage on the secondary. The high current in the shorted turn may be hot enough to boil the oil, and the short may be arcing, which will, of course, break down the oil.
It will probably stop doing this soon, dramatically. I would start enquiries as to the location of a possible replacement transformer.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[itsmoked]

Yeah.. And H U R R Y!

Keith Cress
kcress -

http://www.flaminsystems.com

 

[alehman]

bubbling sound suggesting gases rising in the oil

If your interpretation is correct, you may want to go ahead and shut it down before it shuts itself down, possibly violently. Then start looking for the problem. As the others have eluded, this should not wait until it's convenient or even until a replacement is located.

 

[Zogzog]

Take a DGA sample on that transformer ASAP, and shut it down if possible.

 

[waross]

I'll bet that it shut itself down already.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[itsmoked]

Naw! Not until its shorts some more primary and gets the output up to about 300V so it can take out half the stuff its supplying.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[itsmoked]

BTW: The arcing short is why the lights are flickering.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[prc]

We have to doubt for arcing ( may be from loose connections)to cause lamp flickering.

Take shut down and conduct a single phase low voltage excitation test - it will reveal any turn shortings.

Measure resistances of windings - for loose contacts.

 

[bfuchs]

Gents,

Video of substation fire :

http://au.youtube.com/watch?v=qvoDNKJX7SU

Although I cannot confirm the cause of THIS specific fire one could expect that this is the way most oil-filled transformer which have 'small' internal arcing fault problems would fail : internal arcing faults cause overpressure inside the transformer, an oil leak may develop (unless there is overpressure protection), oil will start spreading outside the transformer until an explosion occurs (catastrophic internal arcing fault), causing hot oil to ignite, and the fire to burn out of control.

 

[itsmoked]

Earth calling roemer.
Earth calling roemer.

COME IN roemer!

Do you copy?




Perhaps he's been occupied with the fire..


Keith Cress
kcress -

http://www.flaminsystems.com

 

[alehman]

This was an external arcing fault, but I fear the results might be similar. Had a bit of an oil leak right before it shut itself down.

http://www.youtube.com/watch?v=fzbQjd_Oo4Q

 

[prc]

My experience with transformer fires is that always an arc in air is required to start a fire.An internal fault or arc under oil will never be the cause for start of fire.Remember arc quenching property of oil that was used in oil circuit breakers.In large transformers, it is bushing failure and arcing in air at top of condenser or bushing terminal that starts a fire.In small units, live internal parts gets exposed to air due to oil leak or oil draining after tank burst which results in internal arcing in air and start of fire.In small units fault clearance time is more so there is time for inside live parts to get exposed to air.

 

[roemer]

Hi,
Thanks for all the comments, seems everybody would like an explosion. The higher voltage 260V on L2 seems to have been present for at least 6 months. The electricity supplier says primary voltage is OK 10KV. The engineer from the electricity board reckoned that sometimes transformers do bubble and it doesn't necessarily mean there is a problem. Suppose the transformer isn't at fault, what could it then be ?

 

[fangas]

I'm not much of a distrabation transformer guy, so the only thing I might add to the above is;

I've been reading in this forum for quite a number of years & those folks that have commented have been around the block quite a bit. Based on their comments, I'd get everyone in authority that said everythings OK, to sign off on their opinion.

Then, you'll have a bit of recourse when that over-voltage transient comes down your line and trashes all manners of things.

Ed

 

[alehman]

We are not wishing for an explosion, but rather trying to help you prevent one. I've personally seen the aftermath of a couple and was hoping to spare you that experience.

For what it's worth, I've never heard of a transformer bubbling being normal.

 

[alehman]

I do hope for the sake of the students in that school that you at least have the decency to have it checked by a qualified testing firm.

 

[burnt2x]

"The engineer from the electricity board reckoned that sometimes transformers do bubble and it doesn't necessarily mean there is a problem."

Which transformer manufacturer is the "engineer from the the electricity board" referring to? I need to know 'cause I don't want to buy "bubbling" transformers from them.
One more thing, you never mentioned what was done to the supply transformer prior to installing your "modern lighting". We are not wishing for an explosion, but possibilities are enormous in your case.

 

[roemer]

We're having the complete substation checked. The transformer is about 35 years old and the only thing that has ever been done is removal of spiders webs and connections tightened.