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Discussion Starter #4

There is that, but doesn't something stop the oil from reaching its flash point?



Funny. That's not far from my place, and I remember when it happened.
I hope you had power in all that :laughing::eek:

You would happen to know the voltages involved?
 

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T
I hope you had power in all that :laughing::eek:

You would happen to know the voltages involved?
I'm about 10 minutes away but I pass by substation often enough. My friend and coworker lives just down the road from there and was without power for awhile after it went up.

They rebuilt it and there's some signage up indicating voltage. I'll have a look next time I drive by.
 

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More than lead and elbows
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It's often a result of age, degradation to the insulation or standing water, that causes a turn to turn fault. Maybe it could be caused by single phasing of underground lines, or sometimes a fault that heats the oil before over current protection kicks in (60 milliseconds). It would scare the crap out of me though.
 

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It's often a result of age, degradation to the insulation or standing water, that causes a turn to turn fault. Maybe it could be caused by single phasing of underground lines, or sometimes a fault that heats the oil before over current protection kicks in (60 milliseconds). It would scare the crap out of me though.
That should read as "suspended water" really....what happens is, over time, the oil in ANY liquid-filled transformer absorbs water, mainly from condensation but sometimes from leaking bushings or other tank parts.

The oil will, up to a point, trap that water and keep it in suspension at levels low enough to not affect the dielectric breakdown point of the oil.

BUT, what can happen (and has happened a lot, mainly in smaller pole-mount transformers) is this: An extended outage allows the oil and transformer internal to cool down enough to the point the water "comes out" of its suspended state in the oil....condensing on the windings' paper wrapping. When the power comes back on.....the result is an internal short which leads to a total failure of the transformer. :eek:

In the case of substation transformers, I have been told that the usual causes of failures like in the video are, in order, switching transients, extended overloading, line faults, lightning, oil contamination (mainly due to neglect) and old age.
 

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Conservitum Americum
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Discussion Starter #17
Whaaaaaa?


Speaka da hinglish?
Sorry phone post :laughing:

I mean if a line short circuited or the transformer had a turn to turn short doesn't something cutout (shut off) the power off to the transformer? Similar to the NEC is a secondary feed from a dry type transformer shorted a breaker would trip.
 

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Or....does it's OCPD react before any given component ignition temperature is reached?

What's scary is this notion seems to be an inherent malady from lowly resi wiring up to sub stations....:eek:

~CS~
 

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Electron Factory.Worker
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A turn to turn short would likely be detected by a transformer differential relay. Normally current in should equal current out (corrected for the turns ratio and slight losses) If excess current is circulating inside the transformer from the short the relay will trip. There is also a sudden pressure device which senses a sudden and rapid rise in the transformer pressure that could trip it as well.

All our oil filled transformers get their oil sampled on a regular basis and they can detect if things are beginning to go south in the transformer.
 
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