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benotype
Commentator

Join Date: Nov 2009
Posts: 89

I am having some challenges with earthing

03/13/2010 8:11 AM
I am working on the earthing of a gas power station,when the resistivity test was done some years ago it was laterite that was present in the chosen location.later on the location was sand filled with white sharp sand and now i am looking for the best possible way to reduce the soil resistance.What i have in mind is to add more rods in parallel,but, my big question is how to add them in parallel and how do i knw how many rods(test wells) i need to add to make up and get the required resistance i want.presently i have not gotten to this level yet but i think i should plan ahead.

Design details(in accordance with laterite sand)(IEE std 80-2000)

Total enclosed area-43500

soil resistivity-143.29

RmS value of symetrical fault current-31.5KA

size of conductor -150mm2

duration of fault current for sizing conductor-0.5 sec

surface resistivity-500 ohm metre

spacing between conductor mat-7m

no of concrete test well -4

rod lenght-3m

diameter-2cm

resistance of earth grid (calculated)-0.33 ohms

NB

can anyone help me with a soft copy of the IEEE standard 80?i'll be very pleased.you can send it to benotype@yahoo.com
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DABRAIN
Associate

Join Date: Mar 2010
Posts: 26
Good Answers: 2
#1

Re: I am having some challenges with earthing

03/13/2010 9:15 AM

Concrete encased electrodes if allowable by local AHJ. Ufer. Avoid the rod. Possibility of using the wells themselves. Depends what the wells are doing and their construction. Need more information. What is the "gas"? "What is gas power?" Is this a natural gas electric power plant or a natural gas utility distribution center (the gas company)?

Endlessly paralleling rods would fail through time. I don't think its a good idea for many reasons. If there is steel or copper encased in concrete in the ground in large amounts, this will give better conductivity to the earth (very general idea.) Read Ufer's work on grounding.

Consult a licensed electrical engineer for this. One who specializes in earthing. There are firms which specialize in this task specifically.

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benotype
Commentator

Join Date: Nov 2009
Posts: 89
#3
In reply to #1

Re: I am having some challenges with earthing

03/14/2010 4:47 AM

Thank you very much for your response,but they are a grey areas in your explanation i will want you to elaborate on.

1)you said paralleling of rods will fail with time,you said it was not a good idea.That strange, i was thinking the more rods you put underground the lesser the resistance of the soil becomes.

2)they are six concrete pit in the design.

The station is suppose to use petroleum gas and its a power genarating plant(250MW).

NB

I observed that the earthing conductors that i have passed through concrete foundations are changing color to black.Do u know of any method i can use to avoid the earthing conductor fom changing colour?The manual states that adequate corrosion protection shall be provided when conductors leave the concrete.I really dont know what method to use.
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DABRAIN
Associate

Join Date: Mar 2010
Posts: 26
Good Answers: 2
#5
In reply to #3

Re: I am having some challenges with earthing

03/14/2010 11:13 PM

each rod will have the same resistance to the earth. there will be no more effective of a low impedance path with one than 20. The addition of rods is to service each source. In this case most likely large turbines powered by the gas. The AC substation rules apply. Most likely everything will be bonded and there will be concrete encased electrodes. I don't see how 250MW could be serviced by ground rods. I guess it could be done.

Get the rules from the respondent who offered them. consult an electrical engineer who specializes on this. Read Ufer's work on grounding. You won't want to use a rod again.

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benotype
Commentator

Join Date: Nov 2009
Posts: 89
#6
In reply to #5

Re: I am having some challenges with earthing

03/15/2010 9:43 AM

@ Dabrain- where can i find ufer's work ?
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electricalexpert65
Guru

Join Date: Oct 2009
Posts: 2061
Good Answers: 169
#7
In reply to #6

Re: I am having some challenges with earthing

03/15/2010 10:06 AM

I will be mailing you now IEEE 80-2000 and Ufer's Paper on Earthing. Pl. acknowledge once you receive them.
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Anonymous Poster
#8
In reply to #7

Re: I am having some challenges with earthing

05/10/2010 7:30 AM

dear sir,

Kindly email me IEEE 80-2000 and Ufer's Paper on Earthing........(girivb@gmail.com)

Thanks
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benotype
Commentator

Join Date: Nov 2009
Posts: 89
#9
In reply to #7

Re: I am having some challenges with earthing

05/10/2010 8:35 AM

I'll really appreciate it if you can send me Ufer's paper.A good samaritan sent me IEEE80-2000.My email add is:benotype@yahoo.com.

Thank you very much sir.
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hkian
Commentator

Join Date: Jan 2010
Posts: 73
Good Answers: 1
#2

Re: I am having some challenges with earthing

03/13/2010 10:48 PM

you can also find this grounding calculations in Substation Engineering Books...

as for me.. i will lessen the soil resistance.. i will put some salts.. then covered it with concrete..

if you are planning for addition rods.. think whether it is cheap or not.. or maybe in your calculations putting addition rods wont resolve this issue.. then you have to lessen the soil resistivity..
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j_rock_ster
Participant

Join Date: Mar 2010
Posts: 1
#4

Re: I am having some challenges with earthing

03/14/2010 4:21 PM

i can email you with a soft copy of the IEEE Guide for safety in AC Substation Grounding.
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electricaleng
Commentator

Join Date: Aug 2011
Posts: 76
#10
In reply to #4

Re: I am having some challenges with earthing

08/24/2011 1:54 AM

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Users who posted comments:

Anonymous Poster (1); benotype (3); DABRAIN (2); electricaleng (1); electricalexpert65 (1); hkian (1); j_rock_ster (1)

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