Grounding at a "service entrance" when there is no service entrance

[AlaskaPE]

Hi there.

I'm working on a project performing a survey of grounding systems at a stand-alone facility in the middle of nowhere.
Since I'm still learning the nuances of grounding systems and their interfaces with power systems, I'm getting hung up on how to approach grounding the service entrance, when there is no service entrance.
My facility has no utility, but rather has a small power station, employing (4) 250kW diesel generators.
The generators are providing power to site facilities, and also to the building I am surveying (I am only surveying the one building).
Power leaves the power station, is stepped up to 7200 kV, travels, and is stepped back down to 208Y/120V at the building. From there it enters an ATS, and then into a primary distribution panel. My question is, for sites that have no service entrance, where should the neutral-ground bond be located?

Thanks.
AlaskaPE

 

[jraef]

Regardless of where the power originates, the first place it enters the facility is the "Service Entrance" from a Low Voltage service standpoint (there may be other regulations regarding the MV** transmission system). So in your case since it appears you are not using the other voltages for anything other than transmission, you would bond the X0 terminal of that 208Y transformer that is supplying your building to ground, and run that as a Neutral into your switchgear / panelboard.

** I'm assuming you meant 7.2kV, not 7,200kV, which would be 7,200,000,000 volts!


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[AlaskaPE]

Thanks. So to reiterate, "service" as in "service entrance" doesn't necessarily have to mean "commercial utility", but any method of power supply, including a wholly on-site generating system? I'm getting hung up on formal NEC definitions, I think. The system has a main and a standby feed, so there are two 7200V transmission lines into the building. They first go into a three-pole ATS, and then to the Main Distribution Panel.

 

[wroggent]

No utility = no service. Ground per NEC 250.30

 

[AlaskaPE]

Haha, yes, thank you. 7,200,000,000V....we're actually planning on sending the power to Mars, have to ensure the transmission level is high enough!

Wroggent, that's what I initially thought as well, but wanted to get outside opinions/discussion.

 

[GroovyGuy]

There is likely no requirement for a 'service-entrance' in the biblical sense. However, there is still a requirement for grounding the neutral, as well as grounding all of the equipment. I would think that the most onerous grounding issue that you will encounter with your setup is touch-and-step potential control at your 208V substations.
BTW, 7200V is odd for a 3-phase distribution voltage. Are you sure it is not 12.47kV 3-phase 3-wire?


"I have not failed. I've just found 10,000 ways that won't work." Thomas Alva Edison (1847-1931)

 

[AlaskaPE]

Hi, thanks for your response. Yes, I'm sure its 7200V.

 

[waross]

The service entrance switch will be the disconnect ahead of the ATS or a service entrance rated ATS.
In the Canadian code, When a utility supplies one of their own office buildings that building is subject to the code. Only generating plants, substations and similar facilities are exempt.
You are your own utility and you have a service entrance to the building. The generating plant may be exempt from the code.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[AlaskaPE]

Hi, thanks for your input. Ok, interesting. So the service entrance switch in this case would be the switchgear breaker before the step-up transformer(the sequence goes, generator, generator switchgear, primary switchgear, step-up transformer, step-down transformer, ATS in building of concern, main distribution panel in building of concern)

 

[waross]

Service entrance is the first switch on the line entering the building. If the 7200:208 Volt transformer is inside the building the service entrance switch may be the 7200 Volt switch ahead of the transformer.
If the 208 Volt transformer is outside of the building the service entrance switch will be a Service Entrance Rated ATS.
Why an ATS inside the building?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[AlaskaPE]

I'm uncertain the original reasoning behind it, the building is located in a harsh environment (artic) so maybe to protect the equipment and make it more accessible in winter? The staff can't tell me much about the original design and there are no drawings. The step-down transformers are outside. Ok, so the (service-rated) ATS can be considered the service entrance switch. It's going to take me a few years to get the hang of this.

 

[waross]

Are there two feeds to the building? Why is the Automatic Transfer Switch in the building when the generators are remote and there is no grid?
Is one side of the switch unused?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[AlaskaPE]

There are two feeds yes. There is a primary power feed and a standby power feed. There are four generators total, two generators feed one section of generator switchgear, two more generators feed one section of generator switchgear. The generator switchgears feed two primary switchgears, joined by a tie-breaker. Each one of those provides a power feed to the building in question.

 

[waross]

Thanks. Each incoming section of the ATS should be treated as a Service Entrance. X0 of the transformers grounded and grounds on each incoming section of the ATS if the neutral is switched. One common ground in the ATS should be acceptable if there is a solid neutral.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[AlaskaPE]

Thanks everyone for all your opinions.