Should transformer core be grounded?
Should transformer core be grounded?
(OP)
We have numerous 1500kva dry type transformers being installed, they do not appear to have the laminations grounded. The steel beam supporting the laminations is grounded but insulated from the laminations.
We've not tested to see if they are grounded but visually they don't appear to be.
We've not tested to see if they are grounded but visually they don't appear to be.






RE: Should transformer core be grounded?
1.Bonding must ensure good electrical contact and remain secure throughout the transformer life. Metalwork which becomes inadequately bonded, creates arcing which will cause breakdown of insulation and oil.
2.No conducting loops must be formed, otherwise circulating currents will result.
RE: Should transformer core be grounded?
I did see a G.S.U. transformer manufactured by Schmitt (Netherlands) where the core was not "solidly grounded", but instead had resistors in the core ground circuit for some reason. Maybe to limit circulating current in the event of a 2nd ground.
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RE: Should transformer core be grounded?
Believe company name is 'Smit Transformatoren BV'
http://www.smittransformers.com/
Interesting idea about resisitve core grounding - I'll have to remember that one.
----------------------------------
One day my ship will come in.
But with my luck, I'll be at the airport!
RE: Should transformer core be grounded?
RE: Should transformer core be grounded?
As an example see ht
See page 7 for description and page 17 for wiring connections.
Other suppliers have similar devices
Maybe your transformer has similar protection
Regards
Luis
RE: Should transformer core be grounded?
The transformers are manufactured in China and badged ABB,
they are installed with no protection other than the electronic WTI Hi temp shunt trip and fuses at the 11kv RMU.
I'm fully conversant with tank earth fault protection our 10mva mobile skid transformers have this.
I'll endeavour to read the standards and also give the core an insulation test to ground.
I have had little experience with these transformers until recent.
Reading info on the web it appears that there are expoxy resin type and another type.
Unsure as to what type we have, but from China they are probably cheap!
RE: Should transformer core be grounded?
grounded (at least, not insulated from the chassis).
I would be very interested to learn about any
potential difference between the core and ground,
if there is any in a healthy transformer. I have
measured a small capacitively coupled voltage on
transformers with electrostatic shielding between
windings, but not often. I would think that there
would be NO measureable current in a loop or T core
unless something was wrong (cracks, separations, etc.)
It would make sense to ground the core as a safety
measure, IMHO. Are pole pig cores grounded?
<als>
P.S. I should add that my experiences are all on
10 Kva or less. Is the big transformer world that
much different?
RE: Should transformer core be grounded?
"The steel beam supporting the laminations is grounded but insulated from the laminations." No duh. This is so the supporting beam does not SHORT OUT the laminations.
All you gnd happy people should take in the PRACTICAL considerations of why the core is NOT gnded. It's not gnded so that it won't produce eddy currents and overheat and burn up. PERIOD.
Oh yes the shock hazard you talk of is GREATLY reduced if one encloses the core in a METAL CASE to keep idiots from touching the ELECTROSTATICALLY CHARGED core and killing themselves. Did I say authorized personnel only? Is there a sticker n the enclosure?
Oh yes, if you went and looked at a TF you would see a little sticker on it that says those nasty metal punched open sided killer T/F's are NOT be installed anywhere accessible to the public. And don't mess with the design. I think it says that too.
Sorry to be abrupt. Let's just be practical for once.
skiier
RE: Should transformer core be grounded?
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RE: Should transformer core be grounded?
As stated above, you are wrong to suggest that transformer cores are left floating.
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Eng-tips forums: The best place on the web for engineering discussions.
RE: Should transformer core be grounded?