Grounding a transformer and a building

[Eclair]

Hi guys

Here is the situation:
I have to ground an old 2 floor building and a new 1.5MVA transformer located behind.

Here is what I would do for the transformer:
-Belt the transfomer with a bare 4/0 copper cable.
-Ground the metal structure of the enforced concrete structure surrounding the transfomer and below the tranformer.
-Ground the metal barrier.
-Ground all this with four 10'x 3/4" copper rods at the four corner of the transformer (each one at 20' distance from another as per IEEE).
-Connect everything with 4/0 bare copper cable.

For the building:
-Surround the building with a 4/0 bare copper cable at 18" of depth with 10'x 3/4" copper rods at the four corner.
-Connect the building with the grounding system of the transformer at 2 location.
-Connect each steel beam of the building to the ground system.

I would like to have some guidelines from you guys cause I can't find anything really useful.

I particulary need:
-depth of stone (rock) to protect the surrounding area of the transformer
-The recommanded area of ground carpet around the tranformer.

I have consulted the IEEE green book for this. It doesn't contain a lot of very useful information.

Thanks

 

[brian john]

I am assuming this is not a sub station you are installing?

I have to ground an old 2 floor building and a new 1.5MVA transformer located behind.

Behind what the building?

Here is what I would do for the transformer:
-Belt the transformer with a bare 4/0 copper cable.

Belt the transformer? Hitting the transformer buys you nothing.

-Ground the metal structure of the enforced concrete structure surrounding the transformer and below the transformer.
-Ground the metal barrier.
-Ground all this with four 10'x 3/4" copper rods at the four corner of the transformer (each one at 20' distance from another as per IEEE).
-Connect everything with 4/0 bare copper cable.

For the building:
-Surround the building with a 4/0 bare copper cable at 18" of depth with 10'x 3/4" copper rods at the four corner.
-Connect the building with the grounding system of the transformer at 2 location.
-Connect each steel beam of the building to the ground system.

I would like to have some guidelines from you guys cause I can't find anything really useful.

This is HV? to 480/277 VAC 3 phase 4 wire?

More than adequate, just check you do not set up a parallel path for ground current (neutral/grounded conductor and EGC conductor [5 wire]) in the transformer secondary service lateral does not set up a parallel path with the neutral/grounded conductor and ground in your service and all electrodes are bonded to form one ground electrode system.

I particulary need:
-depth of stone (rock) to protect the surrounding area of the transformer
-The recommanded area of ground carpet around the tranformer.

Rock? assuming you mean a gravel base around the transformer? I am not sure this is required. But someone here will be more in the know.

I have consulted the IEEE green book for this. It doesn't contain a lot of very useful information.

IEEE any color are excellent books depending on what you are looking for.

 

[tryinghard]

Ground of Premises Wiring (NEC definitions) of grounded systems

Ground of Premises Wiring (NEC definitions) of grounded systems

To understand grounding it helps to back up and ask: why ground?

Keep this clich? in mind: shorts do not go to ground (earth), shorts only try to return to their source and they do this through bonding! Rods do not provide any ground fault protection and they do not give you a safer installation for this purpose.

Ground includes the electrode and the conductor to it, bonding is all the other connections to conductive items which forms a effective ground fault path to source (250-4(A)(5)), and the grounded conductor (250-24(c) & 250-142), also called neutral, is bonded to ground at the service disconnect and separately derived systems to enable ground fault routing to source usually XO of a transformer. These four items make up the grounding system even though they have different functions.

The only reasons for ground rods are described in 250-4(A)(1) ?Electrical System Grounding. Electrical systems that are grounded shall be connected to earth in a manner that will limit the voltage imposed by lightning, line surges, or unintentional contact with higher-voltage lines?. This is why we ground to earth.

So ground is not needed to complete a circuit, it is not current carrying and it is not needed for short-circuit or ground-fault protection. Also the neutral is not ground, the grounded conductor is not ground, and these do not need ground for a circuit to function better, correctly or safely.

The equipment ground conductor, EGC, (250-118) bonded correctly (250 part V, VI, & VII) IS extremely important and integral for ground-fault protection though. Bonding creates the effective ground-fault path from conductive items to source needed to enable ground-fault protection, ONLY if the neutral is bonded at the source and/or service disconnect enabling this path because if its not bonded the path will be disabled and there will NOT be any ground fault protection.

Obviously pictures help for a visual: