reduction of earth grid resistance by addition of earth rods to various grid configurations

7/26/2019 Reduction of Earth Grid Resistance by Addition of Earth Rods to Various Grid Configurations

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Reduction of Earth Grid Resistance by Addition of Earth Rods to

Various Grid Configurations

S. D. Buba, W. F. Wan Ahmad, M. Z. A. Ab Kadir, C. Gomes, J. Jasni1, and M. Osman2

1Centre For !e"troma#neti" and $i#htnin# %rote"tion &esear"h 'C$%(, Fa"u!t) o* n#ineerin#, +niersiti %utra Ma!a)sia, --// +%M

Serdan#, Se!an#or, Ma!a)sia, sanibintahir0#mai!."om

2Deartment o* !e"tri"a! %oer n#ineerin#, Co!!e#e o* n#ineerin#, +niersiti 3ena#a 4asiona!, -/// Ka5an#, Se!an#or, Ma!a)siamis6aina0uniten.edu.m)

ABSTRACT

A"hiein# !o earth #rid resistan"e is hi#h!) desirab!e in oer distribution substations desi#n. 7oeer, due to ariationo* soi! resistiit) *rom one !o"ation to another, it is not ossib!e to obtain the same a!ue o* !o earth resistan"e at a!!

!o"ations. Chan#in# earth "ondu"tor dimensions su"h as "ross se"tiona! area and !en#th ma) !oer earth resistan"e. 8n thisaer, si9 di**erent earth #rid "on*i#urations hae been used to stud) the e**e"t o* addin# erti"a! earth rods to the #rideriher) and at a!! #rid "ondu"tor interse"tions o* ea"h "on*i#uration ith the aim o* redu"in# the oera!! #rid resistan"e.3hree #rids ere desi#ned ith "omression ratio o* 1, hi!e the other three had a "omression ratio o* /.:. &esu!tsindi"ated that *or #rids ith "omression ratio o* /.: and ith earth rods at a!! "ondu"tor interse"tions, the #rid resistan"eas !oer than those ith a "omression ratio o* 1. 8t as a!so *ound that, the resistan"e o* a!! #rids ith a "omression

ratio o* /.: ere !oer than those ith a "omression ratio o* 1.

Keywords; Grid resistan"e, #rid "on*i#uration, earth rods, "omression ratio

843&OD+C38O4A distribution substation is basi"a!!) an e!e"tri"

*a"i!it) "omrisin# o* e


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intera"tie "omuter ro#ram usin# MA3$AB .1/ as

dee!oed in >1-? to a""urate!) "omute the sa*et)arameters o* an earth #rid. 7oeer, there is no aai!ab!e!iterature shoin# the e**e"t o* earth rods on di**erent #ridarran#ements ith the aim o* redu"in# earth #ridresistan"e. 3here*ore, in this aer, the desi#n o* adistribution substation earth #rid as "ondu"ted usin#

CDGS "onsiderin# the e**e"t o* addition o* erti"a! earth

rods to the #rids hose "omression ratio as a!ternate!)"han#ed *rom 1 to /.: in three di**erent arran#ements.

M37ODO$OGH3he ro"ess o* desi#nin# substation earth #rid

desi#n ino!es man) sta#es hi"h hae been out!ined in>?. 7oeer, hen the earth #rid desi#n is done usin#"omuter ro#ram su"h as CDGS, some o* the stesdetai!ed in >? are trun"ated. Basi"a!!), there are todesi#n sta#es, i.e. re!iminar) and a"tua!. 3he re!iminar)sta#e ino!es *ie!d sure) and data "o!!e"tion hi"h is

norma!!) done b) "arr)in# out soi! resistiit)measurements at the a!!o"ated site *or a substation to be

bui!t in order to determine the soi! stru"ture mode!s o*su"h !o"ation. 3he a"tua! desi#n on the other hand"omrises o* "a!"u!ations o* arameters su"h as ma9imume9e"ted #rid "urrent, #rid "ondu"tor si6e, #rid resistan"e,

to!erab!e tou"h and ste o!ta#es, and %& hi"h areautomati"a!!) "omuted b) the CDGS. 8n this aer, anearth #rid has been desi#ned *or a distribution substationroosed to sere a residentia! area su!ied b)1///=A,11E/.-@/.2-= trans*ormer. Soi! resistiit)measurement as "ondu"ted at the roosed substation

site !o"ated at Co!!e#e 12, +niersiti %utra Ma!a)sia,Serdan#, Se!an#or, Ma!a)sia based on Wenner methodusin# a -@%o!e arth 3ester. 3he initia! sa"in# beteen

robes as 1m and in"reased in stes o* 1m u to m. Fora""ura") uroses, the sa"in# beteen robes ase


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3ab!e 2, Soi! mode! "omuted b) &SA%

Soi! $a)ers &esistiit) '@m( 3hi"=ness'm(

1

2

221.

2.-

1.1

in*inite

3ab!e !ists the er*orman"e o* earth #rids desi#nedusin# si9 di**erent "on*i#urations "omrisin# o* three

"ases A1, B1and C1ith "omression ratios o* 1 and three"ases A2, B2 and C2 ith "omression ratios o* /.:,rese"tie!). Fi#ures 1 and 2 i!!ustrate the #rid

"on*i#urations *or A1and A2ith "omression ratios 1 and/.:. 8t "ou!d be obsered *rom 3ab!e that a!thou#h thetota! !en#th o* buried "ondu"tors *or both A1 and A2 issimi!ar, i.e. 2-/m, the #rid resistan"es ere s!i#ht!)di**erent ith -./-1 *or A1and -.: *or A2#rids,rese"tie!). 3his indi"ates that "omression ratio has a

s!i#ht e**e"t on earth #rid resistan"e een in terms o*/.1 di**eren"e on!). Considerin# the %& ith rese"tto the to #rid "on*i#urations, ith an ener#i6ation "urrento* ma#nitude ./=A, it is obsered that the #rid ith A 1

"on*i#uration had an %& o* 2.:=, hi!e an %& o*2.= as obtained *rom A2#rid shoin#a di**eren"e

o* 211 hi"h is su**i"ient to "ause a sho"= ha6ard,ese"ia!!) to ersonne! ho are dire"t!) or indire"t!) in"onta"t ith e


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interse"tions. 8n terms o* %&, the a!ue re"orded *rom

#rid C1 is si#ni*i"ant!) !oer than that *rom #rid A 1 b)1,1 hi"h is dan#erous!) hi#h. A!so, "omarin# C2and A2, it "ou!d be seen that the %& obtained *rom #ridC2 is )et !oer than #rid A2b) 1, hi"h "ou!d beotentia!!) ha6ardous to ersonne! and other !iin# thin#sin the i"init) o* the substation. Comarin# the a!ues

%& *or A1, B1 and C1 ith A2, B2 and C2 #rid

"on*i#urations, it "ou!d be dedu"ed that, earth #ridsdesi#ned ith "omression ratio o* /.: hae !oer %&than those ith a "omression ratio o* 1. 8m!ied!),"omression ratio has a si#ni*i"ant e**e"t on %&ese"ia!!) hen erti"a! earth rods are insta!!ed at a!! #rid

"ondu"tor interse"tions. Simi!ar!), re!atin# the a!ues o* *or A1, B1and C1#rids ith A2, B2and C2#rids, it is "!earthat there is no si#ni*i"ant "han#e in the a!ue o* desite the in"rease o* buried "ondu"tor !en#th in B1, B2and C1, C2 #rid "on*i#urations. 8t is a!so eident *rom3ab!e that, "omression ratio has ne#!i#ib!e or no e**e"t

on the a!ue o* as it as "han#ed *rom 1./ to /.:.

4ote that the buried "ondu"tor !en#ths *or #rid A1and A2are simi!ar desite the di**erent "on*i#urations. 8n the sameein, B1and B2are simi!ar, C1and C2are a!so simi!ar asindi"ated in 3ab!e . Comarin# the #rid "on*i#urationsa""ordin# to t)e A, B and C ith re#ard to buried

"ondu"tor !en#th, it "ou!d be seen that #rid C has thehi#hest !en#th o* buried "ondu"tor "omrisin# o* strandedbare "ondu"tors and earth rods both made o* "oer at a!!#rid interse"tions. Grid "on*i#uration B has the ne9t

hi#her !en#th o* buried "ondu"tor a!so in"!udin# earthrods, hi!e #rid A had the !east !en#th o* buried "ondu"tor

ithout rods. 3)i"a! a!ues o* buried "ondu"tor !en#thsare -2m, 1:/m and 2-/m, rese"tie!).

3ab!e - !ists the "ost o* buried "ondu"tors *or theea"h o* the #rid "on*i#urations. 3he "ost o* 1 metre !en#tho* -E/ AWG '/./1-m diameter( stranded bare "oer"ondu"tor *rom Southire "ata!o#ue is MH&.//, hi!e

the "ost o* one metre !en#th o* /./1m diameter earth rod

*rom !ement 1- "ata!o#ue is MH&-1.//. 8t "ou!d beobsered that the "ost o* 2-/m !en#th o* stranded bare"oer "ondu"tor ma=in# #rid "on*i#uration A isMH&1/2,//.//. Simi!ar!), the "ost o* 2-/m o* bare"oer "ondu"tor !us 2-/m !en#th o* earth rods '1:/m(

#rid "on*i#uration B is MH& 112,-/.//. 3he "ostdi**eren"e beteen #rid "on*i#urations A and B is MH&,:-/.//. 8n the same ein, the "ost o* 2-/m o* bare"oer "ondu"tor and 12m o* earth rods '-2m( *or#rid C "on*i#uration is MH&1,1-.//. 3he "ostdi**eren"e beteen #rid A and C is MH&-,2-.// and

beteen #rid B and C is MH&--,-/.//. Based on "ost"omarison and the a!ue o* obtained *rom #rids A, B

and C, it is obious that #rid C "on*i#uration is note"onomi"a! to "onstru"t as the "ost o* buried "ondu"tor iser) hi#h "omared to the "ost o* #rid "on*i#urations Aand B, a!so the "han#e in the a!ue o* is not si#ni*i"ant.

3ab!e - Cost o* buried "ondu"tors

arth GridCon*i#uration

$en#th o* BuriedCondu"tor 'm(

Cost 'MH&(

ABC

2-/1:/-2

1/2,//.//112,-/.//1,1-.//

CO4C$+S8O4A stud) o* the e**e"t o* earth rods on redu"tion o*

#rid resistan"e usin# si9 di**erent earth #rid "on*i#urationsas resented. 3o arameters ere "onsidered, thesa"in# beteen #rid "ondu"tors o* "omression ratio 1

and /.:, and earth #rid "on*i#uration in hi"h one asinsta!!ed ithout an) erti"a! earth rods, hi!e anotheras insta!!ed ith erti"a! earth rods at the #rid eriher)and the !ast ith erti"a! rods at a!! #rid interse"tions. 8tas *ound that, #rids desi#ned ith "omression ratio o*/.: )ie!ded !oer #rid resistan"es than those ith

"omression ratio 1. 8t as a!so reea!ed that the #rid

resistan"e obtained a*ter insta!!ation o* earth rods at a!!"ondu"tor interse"tions as ne#!i#ib!e "onsiderin# thein"rease in tota! buried "ondu"tor !en#th. Furthermore, itas dis"oered that, the %& rodu"ed b) #rids desi#nedith "omression ratio /.: ere !oer than those ith

-8 8 24 40 56 72

X AXIS (METERS)

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Fi#ure - 3o ie o* earth #rid B2

-8 8 24 40 56 72

X AXIS (METERS)

-8

8

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YAXIS

(METERS)

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Fi#ure 3o ie o* earth#rid C

1

-8 8 24 40 56 72

X AXIS (METERS)

-8

8

24

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72

Y

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(METERS)

Fi#. 3o ie o* earth #rid C2


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"omression ratio o* 1. 8t "ou!d there*ore be "on"!uded

that, insta!!ation o* earth rods at a!! "ondu"tor interse"tionsin a #rid ith the aim o* redu"in# the #rid resistan"e is notre"ommended as the redu"tion in resistan"e '/.11( is not"ommensurate to the in"rease in buried "ondu"tor !en#th'1/:-m(.

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reduction of earth grid resistance by addition of earth rods to various grid configurations

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