Industrial Grounding - Oil/Gas/Process Plants

[NickParker]

For large industrial plant extended over a large area in which there are typically several electrical rooms, How grouding is designed?.
The substation / Switchyard is designed using IEEE-80-2000 and how about other plant areas.

My understanding is as follows,

1. Breakdown the plant area as per the process.
2. Make own grounding grid for the particular process area. (What is the IEEE specification to design the plant area)
3. The main substation has another grounding grid. (Designed using IEEE-80)
4. Interconnect all the grounding grids at the respective area to the substation grounding grid.

 

[wbd]

Since this is inside an industrial facility, assuming this is in the USA, you would have to follow NFPA 70,the National Electric Code, Article 250 Grounding and Bonding.

 

[7anoter4]

In my opinion,IEEE 3007.3/2012 it has to be suitable for industrial plants.

https://beyondstandards.ieee.org/power-and-energy/3000collect/

 

[krisys]

In the industrial plants mainly in oil & gas, petrochemical and process industries you may see the below type of earthing/groundings (let me call earthing for the convenient):-
[ul]
[li]Power system earthing (manly transformer neutrals)[/li]
[li]Equipment earthing[/li]
[li]Pipeline/pipe earthing (jumpering)[/li]
[li]Instrument earthing (again subdivided into IS earthinng and non-IS earthing); IS stands for Intrinsically safe[/li]
[li]DC system earthing[/li]
[li]Lightning protection system earthing[/li]
[/ul]

So the entire earthing itself is a domain. This is governed by multiple international standards and company specific standards. Strictly speaking IEEE-80 is only for the substation grounding.

 

[NickParker]

While I read more on this topic, I have some more questions,
1. Is it okay that step potential & touch potential need not be calculated for the Indoor substation as I get to hear from some of my colleagues? and also for the building which has a concrete floor & all the cables entering the premises are insulated and carried by conduits and raceways.
2. As I read the IEEE-80, the fault current at the primary of the substation is used to calculate the GPR, Step & touch potential and the maximum fault current (usually at LV Switchgear) at the substation/Plant is used for conductor sizing. Is my understanding correct?
3. Only the Line to ground fault from the ETAP study to be considered for the conductor sizing, GPR, Step and touch potentials?
4. For the plant areas which have the equipment, the owner usually specifies the minimum ground conductor and that is to be connected to the main ground grid and do not have any standards to follow.
5. If my switchgear fault level is 65kA, 1sec and the ETAP calculated values are 51kA & the relay tripping is set at 0.5sec, which values do I need to consider for conductor sizing? switchgear fault level or ETAP calculated values?

 

[7anoter4]

1)GPR, touch and step potential are produced when a current passes through ground resistance. This current is generated outside the substation and reach the substation through [deep] ground. The current generated above the grounding grid and supplies only above the grid equipment passes only through the grid conductors [a very small part flows through ground as parallel path, indeed]
2)The outside generated short circuit current entering directly an equipment [post, switchgear, transformer or else] grounded through grounding grid, minus the return current through grounding wire, static wire, shield, armor or else] it is to be considered.
3)The maximum from line-to-ground and double line to ground .
5) In my opinion ,65 kA 1 sec is the switchgear rating but the protection should be set up according to the prospective [real] current and to protected equipment [cable mainly].

 

[jghrist]

Grounding conductor sizes are based on either the service entrance conductor size or the overcurrent device rating/setting in accordance with NEC Article 250.