Primary Switchgear Grounding

[strap89]

I know when you have a utilization voltage service transformer, you bond the neutral and ground buses at the service entrance equipment and from that point you are running 3P, 4W, plus an equipment ground through the whole system.

The question I have is with primary switchgear used to distribute power through a campus. Say you have a grounded wye connected 13.2 kV substation with three phases and a neutral that feeds a 3P, 3W (Three phases and one ground bus, not sure if 3P, 3W is a correct classification) primary switchgear of the same voltage. I'm noticing that the gear does not have a both a neutral and a ground bus, but a single ground bus. Should the neutral from the substation be tied directly to the singe ground bus, as well as the switchgear grounding electrode system? I'm confused because typically I'm used to seeing a neutral and a ground bus in 480V gear. It seems to be when talking about "neutral" and "ground" at a primary switchgear, the terms are interchangeable and both the neutral and the electrode system are tied to the same bus.

Second question. If I don't run the neutral from the substation to the ground bus in the primary gear, and just establish an electrode at the gear, is the system still grounded because the substation transformer upstream is grounded?

Thanks!

 

[GoldDigger]

If the supply to a building is coming from a distribution point after the POCO service point, IMHO it has to be treated as a feeder and not a service, regardless of the voltage level.
But there may be different provisions in the code for grounding and bonding at MV and HV levels.

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[Corytr]

3P 3W would be a correct description of a true delta system or an ungrounded wye system. However, you describe a grounded 4 wire wye system. On the utility side of things, the more points that you can tie your system neutral to the earth, the better. There are minimum requirements of doing so in the NESC. So, yes, the primary neutral should be tied to the common ground bus. In fact, the concrete vaults that utility companies use are bonded as well. They are interlaced with copper, etc that adds to the quality of the ground. There is no better ground in the utility world than the system neutral. Yes, the primary neutral is usually directly bonded to the secondary neutrals as well

As far as your second question, you need to use a neutral if you are going to be connecting any loads in a true wye configuration. Just establishing an electrode at the gear would most likely not be an adequate return path for the current as the earth has an impedance much greater than that of a neutral. You could use delta connected transformers/gear and get away without using a neutral. You could use a line to line connected single phase transformer and get your standard 120/240v service. This would work because the connected equipment would reference the difference in potential of the secondary coil of the transformer and not that of the earth.

As far as considering it "adequately grounded" with just a ground rod, that would take some ohm readings to ensure it is below the threshold to consider it adequately or effictively grounded.

Just a disclaimer: My perspective is entirely from the Utility side of things.