Transformer Grounding

[acdc]

In a 3000 kva transformer 4160/480v , should you bond xo
to the transformer equipment ground, which is ground to the power company ground.

 

[jbartos]

Suggestion: Please, elaborate on the system grounding.

 

[acdc]

WE HAVE A 15 MVA SUBSTATION , THE PRIMARY VOLTAGE TO THE SUBSTATION IS 115K THE SECONDARY IS
4160. WE HAVE A EXISTING M.C.C. WHICH IS FEED FROM THE SUBSTATION THOUGH A 2000A O.C.B.,
WE RECEIVE THE 2000A 4160V INTO OUR M.C.C. WE THEN DISTRIBUTE THE 4160 TO SEVERAL MED.
VOLTAGE MOTORS AND TWO 4160/480V TRANSFORMERS WHICH FEED OUR LOW VOLTAGE M.C.C.S.
THIS SYSTEM HAS A GROUND GRID WHICH GOES THOUGH THE WHOLE FACILITY AND IS TIED BACK INTO
THE SUBSTATIONS GROUND SYSTEM . WE ARE ADDING ANOTHER 1200A O.C.B.IN THE SUBSTATION.
WHICH WILL FEED THE 3000 KVA TRANSFORMER. MY QUESTION WAS SHOULD I BOND XO TO THE
EUIPMENT GROUND OF THE TRANSFORMER WHICH WILL BE GROUND TO THE THE MAIN GRID.
THIS 3000KVA TRANSFORMER IS FEEDING A MCC THE XO WILL BE ATTACHED TO THE GROUND
OF THE MCC AND IT WILL BE BOND TO THE MAIN GRID OF THE FACILITY . BUT DOES IT MATTER IF
I BOND IT TO THE EQUIPMENT GROUND AT THE TRANSFORMER.

 

[jbartos]

Suggestion: Your new 3000kVA 4160Vdelta/480Vstar (delta/star assumed) may have its star neutral solidly grounded. This implies solidly grounded neutral system grounding. Therefore, xo's may be connected to the equipment ground, if high resistance system grounding, medium resistance system grounding, or similar system grounding is not preferred to the solidly grounded system neutral (not so frequent requirement, since it applies to expensive processes and potentially bigger losses in case of ground fault trips). Incidentally, there is a difference between equipment grounding and system grounding. See IEEE Std 142-1991 Green Book or visit

http://www.ieee.org

for its latest version procurement.