Medium Voltage Ground Grid

[xguard]

I work for a government agency (not popular I know). We have a facility we are rehabbing with an incoming utility voltage of 2.4 kV 3-phase. Our side of the utility transformer is 480/277 3-phase. A consultant is telling us a grounding grid at our facility is required to limit step and touch voltages at the site in the event of a medium voltage ground fault. They want to perform a "MV grounding requirements analysis" based on IEEE 80 "Guide for Safety in AC substation Grounding". I'm a little leery as I have not encountered this before and our facility is not a substation but a tunnel and ventilation building for the tunnel. Is this type of study and grounding grid typically used outside of substations?

 

[Elect117]

I would not do the ground study. It sounds like they are adding some stuff to bill you more. Your applications seems simple. Minus any additional rules regarding back up power, life safety systems, etc.

 

[don_resqcapt19]

That IEEE document only applies within a substation, and should be complied with withing the substation. The study should be limited to the physical area within the substation fence.

 

[Julius Right]

See NEC [NFPA-70/2023] Part X. Grounding of Systems and Circuits of over 1000 Volts 250.180 General.
However, if installation falls in case of (2) Installations underground in mines and self-propelled mobile surface mining machinery and its attendant electrical trailing cable-as per NEC art.90-you have to follow the other specific standards as NFPA 120 or 122 -I think.

 

[jim dungar]

That IEEE document only applies within a substation....

Our industry slang gets in the way again.

This document is basically for substations with open air overhead conductors.

Totally metal enclosed switchgear, installed under the NEC, is not subject to IEEE 80 even though our industry calls this equipment a substation.

 

[xguard]

Our industry slang gets in the way again.

This document is basically for substations with open air overhead conductors.

Totally metal enclosed switchgear, installed under the NEC, is not subject to IEEE 80 even though our industry calls this equipment a substation.

The only medium voltage equipment is the utility company's transformer. Our switch board and equipment is 480/277.

 

[jim dungar]

The only medium voltage equipment is the utility company's transformer. Our switch board and equipment is 480/277.

My guess is the utility transformer a totally enclosed pad mount style. The secondary conductors are most likely customer owned and installed per the NEC, including bonding of the transformer case.

If it is a transformer with exposed parts, I would think the utility would have the ground grid and fencing specifications.

 

[zbang]

The only medium voltage equipment is the utility company's transformer.

After all that above, look at what the utility usually requires for similar equipment (probably nothing special for a GES).