Previous in Forum: Indoor Termination   Next in Forum: What is DDC Panel in Switchgear
Close

Comments Format:






Change Mode
Close

Subscribe to Discussion:

CR4 allows you to "subscribe" to a discussion
so that you can be notified of new comments to
the discussion via email.

Close

Rating Vote:







Add Vote
6 comments
Rate Comments: Nested
doozysg
Participant

Join Date: Dec 2014
Posts: 3

Touch and Step Potential for Multi-Story Substation

12/19/2014 9:48 AM

Hi Forumer,

Would like to seek experience on doing simulation/calculation approach for an 8 storey 66/22kv substation. I have a current job and the consultant has designed reinforcement square grid mesh on cable floor (5th floor) and 66kv switchgear floor (6th floor). The square grid mesh is comprising of size 200mm x 200mm, diameter is 13mm. The specification states 650sqmm/m.

Basically, the whole floor for both are laid with the mesh with few number of earth bar - min. 600sqmm, connected to 2 points of the mesh via 300sqmm copper bar. From each earth bar, it is connected to lower floor down to ground floor to various earth pits. For other design, they are further connected to a ground grid comprising of 600sqmm conductor in square grid across the whole footprint of the station.

Back to this station design, the consultant is seeking the contractor to engage specialist to conduct studie evaluate the step and touch potential of the substation.

My thought is there should bot a need for studies for any grid system in floor other than the ground since any fault current should channel through the earthbar (bond to equipment) down to ground grid via earth conducted. And there should be no bonding of earthbar to cable floor and switchgear floor concrete slab reinforcement grid. By bonding them, we are effectively introducing potential on the concrete slab which in turn create step potential. Even if it is bonded, the full 50KA 3sec fault current is unlikely to be running down the rebar mesh down to ground via the connected reinforcememt since there is a better path for fault current via earthbars and conductors. This is assuming that path has lower resistance compare to reinforcement path.

So the question npw is if we were to use commercial available software to do simulation, what type of model should we adopt since most concept is based on 1 storey substation design, that is only one grid.

Anyone here has idea or experienced?

Thank you
Register to Reply
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

"Almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, vote them!
Fredski
Guru

Join Date: Feb 2011
Posts: 7025
Good Answers: 207
#1

Re: touch and step potential for multi-storey substation

12/19/2014 9:55 AM

looks like they awarded the wrong person this job
Register to Reply Score 1 for Good Answer
No more "Almost" Good Answers.
doozysg
Participant

Join Date: Dec 2014
Posts: 3
#2
In reply to #1

Re: touch and step potential for multi-storey substation

12/19/2014 10:03 AM

Hi Fredski,

This is a specialist work on the simulation part and I am the contractor to do the grid system to engineer's design. I am definitely not the right person to do the study but will engage a professional engineer. But having talk to a few of them, each has their own concept so I thought for the benefit of knowledge, I could tap the experience of people here to better interpret the result generate.

Thank you.
Register to Reply
North of 60
Guru
Canada - Member - If there is a way to screw someting up, there is someone to do so! Safety - Hazmat - New Member

Join Date: Mar 2007
Location: Iqaluit, NU. Canada
Posts: 1854
Good Answers: 140
#3

Re: touch and step potential for multi-storey substation

12/19/2014 12:07 PM

I get the rather distinct impression from your comments that you believe that fault currents flow to ground. That is only true if the path back to the source is via the ground. Fault current returns to its source via ALL available paths. So... if the return path is through bonding conductors back to the transformers... the vast majority of the fault current will flow that way and not necessarily to "ground".

__________________
 Joe Contractor to Electrical Inspector, "What do you mean you are going to make me follow the code?".
Register to Reply
Fredski
Guru

Join Date: Feb 2011
Posts: 7025
Good Answers: 207
#4

Re: touch and step potential for multi-storey substation

12/19/2014 12:56 PM

you might find this valuablehttp://electrical-engineering-portal.com/neutral-single-earthed-or-multi-earthed
Register to Reply
7anoter4
Guru

Join Date: Oct 2012
Location: 100 miles North from the World Center
Posts: 879
Good Answers: 42
#5

Re: Touch and Step Potential for Multi-Story Substation

12/20/2014 11:48 AM

I think the grounding grid in the floor was required in the past in order to protect sensitive equipment. I don't know if this is now still required.

The recommended standards are:

IEEE 1100/2005

IEEE Recommended Practice for Powering and Grounding Electronic Equipment (IEEE Emerald Book).See [also]:

http://standards.ieee.org/findstds/standard/1100-2005.html

IEEE Std 142-2007

IEEE Recommended Practice for Grounding of Industrial and Commercial Power Systems. [IEEE Green Book].

__________________
 Julius
Register to Reply
doozysg
Participant

Join Date: Dec 2014
Posts: 3
#6

Re: Touch and Step Potential for Multi-Story Substation

06/03/2015 5:07 AM

Hi,
Thank you for the comments and feedback.Some updates and appreciate further guidance.I have engaged specialist to conduct a soil resistivity test and subsequently earth grid simulation.
The earthing layout is as attached in photo.What I would like to seek is how do you interpret the earthing layout and what are the parameters we should adopt when inputting it into software.Basically, I have read a few software available and I think most are only suitable for ground grid system. In this case, it is a multi-storey grid system. As such, what value of fault current will run through from top to ground? When determining the touch and step potential, we need to input the fault current injected into say the upper floor assuming it is a ground fault at 6th floor.
Appreciate any comment.Thank you.
Register to Reply
Register to Reply
Have a Different Question?
6 comments

"Almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, vote them!
Copy to Clipboard

Users who posted comments:

7anoter4 (1); doozysg (2); Fredski (2); North of 60 (1)

Previous in Forum: Indoor Termination   Next in Forum: What is DDC Panel in Switchgear

Advertisement

Got Something to Say?
Ask a Question
Start a Discussion

Search this Forum
Electrical Engineering:
Go

CR4 Sections
Aerospace
BioMech & BioMed
Chemical & Material Science
Civil Engineering
Communications & Electronics
Education and Engineering Careers
Electrical Engineering
General Discussion
Instrumentation
Manufacturing
Mechanical Engineering
New Technologies & Research
Software & Programming
Sustainable Engineering
Transportation

Site Directories
Forum Directory
Blog Directory
User Group Directory
RSS Feeds

CR4 Rules of Conduct
CR4 FAQ
Site Glossary

Who's Online (71 right now)
Show Members
Advertisement