wye to wye transformer grounding 1

[hhsting]

I have customer owned 2000kva transformer wye to wye primary 13.2kv to secondary 600V used for solar farm. The transformer primary is fed from customer owned 13.2kV SWBD. The service point as defined in NEC 2014 is at 13.2kV Swbd which has fused disconnect to the transformer. I have 3 concentric neutral cables coming to primary transformer which has H1, H2, H3, ground pad which maybe for tank ground not sure. The transformer secondary has X1, X2, X3, H0/X0, ground neutral strap, ground pad which maybe tank ground not sure. H0 and X0 is bonded internally. The transformer secondary feeds 600V SWBD which has neutral to ground bond, grounding electrode gnd ring and grounding electrode conductor. 13.2kV Swbd, xfmr and 600v swbd are all in one concrete pad outside in fenced compound. AHJ that project located is in NEC 2014.

I am having hard time figuring out how to properly ground and bond the transformer. Where does concentric neutral land HV compartment their is no neutral bushing or goes to X0/H0 LV compartment where their is also LV neutral? Is the transformer separately derived? Can their be neutral to ground bond and 600V SWBD have grounding electrode conductor to ground ring?

Anyone experience with wye to wye grounding and bonding can you help? Will post transformer name plate and compartment datasheet.

 

[jghrist]

NEC 250.184. The solidly grounded primary system is permitted to be multi-grounded. The utility system is most likely solidly grounded. The fuse protection in the 13.2 kV switchboard will not be affected by ground currents in the neutral.

A grd wye - grd wye transformer is not a separately derived system. The X0-H0 connection should not be disconnected, even if it can. It will force a secondary ground fault to return through the earth instead of the concentric neutral, which serves as the grounding conductor.

 

[hhsting]

@Stevenal (Electrical) I thought this would be covered by Nec. Nec Article 690 covers solar panels and generation. Nec Article 250 part X covers grounding and bonding over 1000V.
We had once engineering firm who submitted plans for public electric utility substation we told them take these plans and dont ever come back here. I mean Ever in future.
What NEC does not cover is public electric utility owned and operated generation, transmission, substation as stated in Nec Article 90.2 which is covered by NESC. However, what I have is privately owned solar farm and mini substation that feeds electric utility grid.
How did you figure this would be covered by NESC? Can you please tell me more? I never laid eyes on NESC only NEC. We dont enforce NESC.

 

[jghrist]

Attached sketch shows wiring from 13.2kV SWBD to 13.2kv to 600V wye to wye xfmr. Would this be something that is normal wiring for transformer such as this?

This sketch shows normal wiring and meets NEC in my opinion.

 

[cuky2000]

.
If the job is not done by an electric utility such as IPP, design by am engineering consulting firm, it is our experience that the generating plan will follow the NEC. Primarily this is because of liability concerns and compliance with the territory over the IHJ on the project.
_{NOTE: many utilities and consulting call the Control House or PowerHouse as Control Cubicle to avoid being under the building code.}

If you are in the State that adopts the NESC, them it is mandatory to comply with the NESC. See the 2012 survey as a reference Link
State such as California has the own safety code enforced by the State of CA. However, our experience indicates that if there is compliance with the NESC, there is a good chance to meet the requirement of the local code.
All the utilities that I know and even the ones located in states that not support the NESC, in practice fallow the safety rules per the NESC.
For some history associated with the NESC, see the following Link

 

[stevenal]

Utility facilities and functions of utilities that either (a) generate energy by conversion from some
other form of energy such as, but not limited to, fossil fuel, chemical, nuclear, solar, mechanical,
wind, or hydraulic or communication signals or accept energy or communication signals from
another entity or (b) provide that energy or communication signals through a delivery point to
another entity

Similar systems to those listed above that are under the exclusive control of qualified persons and
authorized by a regulating or controlling body, including those associated with an industrial
complex or utility interactive system.

I would say an independent power producer acting under contract with a utility is performing the function of a utility.

 

[cuky2000]

Our company designed multiple power plants, transmission and distribution systems for several power authorities including TVA, NYPA, Government utilities such as SRP and private utilities such as PSE&G and ConEd, FP&L among others and the project was designed in compliance with the NEC.

Probably the T&C was agreed for liability reason and meet the insurance requirement, bank and others. If the project is done by the self-insure capability of the utility and releases the designer for any insurance/vendor guaranty issues, there is a possibility that a private consulting firm could accept this transferring any responsibility to the owner. This could be a tough call for the utility procurement folks to accept that in the contract.

It should be noted that there are significant differences between utility practice and commercial private practice following the NEC in areas such as grounding method, wire sizing among other, etc. Our corporate attorneys and the contract department usually taking a strong position in this matter based on bad experience and lawsuits in past projects experience.

An interesting anecdote happens a few years ago in several solar projects owned by a utility. The State refused to inspect them since under the premise that the utility is exempted to comply with the NEC. The utility hire us a consulting to act as the independent party acting as IHJ to allow the metering department to interconnect the solar projects to the same utility system.