Broken in Some Rings in Post Insulator

There should be some instructions in the substation documentation. You should already know this. Find it and read it.......................

We can't see the documentation that you have.

Insulator (electricity) - Wikipedia, the free encyclopedia

This sounds like how the dive tables were worked out.

If it looks broken, it probably is!

That being said: take it out of work and fix it before it is too late!

There's a reason why you "...have a lot...broken...", it's probably because they were under-designed to withstand the short circuit forces that they were subjected to. Replacing them without understanding why they broke is only inviting the new ones to fail as well.

You cannot calculate the creepage distance of broken insulators, that will only lead to outages at the worst possible times.

Must agree with Wal... you are over thinking this WAY to much..

I got a word for you... Maintenance. Nothing more, nothing less!

Now for a Q&A!

Q. Does it look broke? A. not sure, lets look at it!

Q. Now you've look at it, is it broke? A. Yes!

Q. What the best plan to resolve this problem? A. Replace it and find out why its broke!

Q. when was the last time you looked at it? A. Not sure... DUH!!

Q. How old is it? A. Not sure!

please feel free to submit your own answer for mine...

Read some manuals and texts for high voltage transmission. Everything is clear there .. may be your SS manuals also have it. go thru .

REPLACE THEM!!!!

I agree with all those here that said to replace them as broken rings can collect dust/moisture/who knows what and become a danger. A second rupture on the same ring may cause a short circuit as parts drop off for example....

Furthermore, you need to try and understand why they are breaking, is it poor manufacturing quality or poor installation of them when new, as we have no pictures or other help, it is not possible for us to be certain.

Contact the manufacturer and send him broken examples.....

Possibly if they are under too much compression when installed for example, changes in temperature may cause them to rupture....just a thought. Low temperatures can be just as damaging as high, with metal parts changing in size quite dramatically - smaller/shorter for example.

I am guessing that where you are it got cold this winter!!!

It would help us more to know your location on this world!!!!

Truth is, this is not scientific, rocket science or formula driven and forget cost, replace them as the next one will blow and take out more than you bargained for.

The break has changed the surface tensions and stress has increased in the porcelain, so forget your minimum creepage distances, it is irrelevant now. An exploding porcelain insulator is like a hand grenade, it will cause great damage. And someone may just be nearby to receive a lump of porcelain in the face or head. So what good is your cost saving and creepage formula when you have an injury to pay for.

Common sense and maybe safety should be the driving factor!!!

If the insulators are broken on the outside where you can see the break, then they have microfractures on the inside that you cannot see. Replace them as soon as possible. If the higher ups or bean counters complain, point out that you are in breach of the regulations and you are not insured.

Just one source:

High voltage leads for ratings 2.4 kV and up are normally brought through the tank end wall using a porcelain bushing. To prevent excessive mechanical loading of the bushing, only flexible connections should be made to the bushing terminal. The bushing should never be used as a structural member to support other current-carrying parts.

Care must be taken in handling the bushing to avoid cracking the porcelain or damaging its surface. Should it become necessary to replace a bushing or its gasket, proceed as follows:

1. Vent the tank to the atmosphere until pressure is zero.

2. Lower the liquid level to a point below the bushing
level.

3. Remove the nuts and washers used to clamp the
flange of the bushing.

4. Pull the bushing outward as far as necessary to replace
the gasket and/or to unfasten the cable connection at
bushing inner end.

When reinstalling the bushing, install a new gasket in the gasket recess on the underside of the flange to insure that the gasket is properly seated in the groove. A flat washer
and lock washer should be placed between the mounting nut and the flange. After the nuts are finger tight, each one should be tightened to a torque of 60±5 inch pounds.

After completion, pressure test the transformer.

If you insist:

Testing and Maintenance of High-Voltage Bushings

....and if these simple installation practices were followed then the insulator(s) wouldn't have cracked in the first place.

Using electrical connections for mechanical restraint of conductors rarely ends well.

Don't you think it is wise to refill the Tfx with oil and do an oil dielectric test and check for moisture and CFC and maybe test for acetylene gases?

If the Tfx is out of service for bushing replacement, please do the full job and not a half job. And check the oil dielectric before refilling the Tfx tank and conservator tank, (If it has one). And also, check the new oil dielectric before use.

If you replace Tfx bushings, it is not a quick unplanned job. And use neoprene impregnated cork gaskets, they are less likely to leak latter in life.

GA....

GA...? Sorry, i have no clue what this may mean or transpire to mean. Can you elaborate and then I can LMAO.

Good Answer

Thanks for that, to both of you. Rgds

I don't have a local set of instructions for this service. We have a depot to do the work.

I basically pulled the first valid reference I found...just to give the guy and idea that his equipment needs rework. He shouldn't be trying to figure out if they can still be used while broken in two places.

Your points are well-founded and sage advice.

Dear Asser,

Don't waste time on calculating creepage distances as economics wont be in favour. It may spoil your transformer if you are concerning that or may cause a serious accident causing damages much more than the required investment. You may learn of calculating creepages on a later date. Lets not hope you come accross a situatiopn of paying compenmsatiuon. For bushings contact transformer manufactures or any high voltage equpment vendor.

Dont delay.