grid resistance & pit resistance

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Dear Sir,

I have a problem In my 220kV Substation .Grid earth resistance is less than 1 & individual earth pit resistance(disscunnected from grid ) is more than 2 ohm. Is it ok

let us consider 3 pit resistance is

1. P1=X
2. P2=Y
3. P3=Z

So Total Grid Resistence Will Be

Grid=X+Y+Z

So total grid resistence should be less than 5

So pits resistence should be as sothat there all sum should be less than 5

Yes mr pandit! you are wrong! Resistances are in parallel. not in series as you answered.

Dear Sir

As i know that in grid all resistence should be in series so if all will in parrell then if valu of pit resitence is low then Grid valu will be large

GRID RESIANCE =1/X+1/Y+1/Z for parell restence if X,Y,Z will be large then only grid resitence will be low which is not possible if I wrong kindly make me clear Thanks

Do you have IEEE 80?, go through pl.

Dear sir

i check all through IEEE 80 but not get satisfactory answer kindly make it clear sir i will be thankfull to you for this

sir,

as i know If a grid is made of lets say 4 nos. of earth pits.

A= W+X+Y+Z

Total Grid resistacne should be 1/A = 1/x+1/Y+1/z+1/W

My question is that do i need to measure the individual earth pit resistance while disconnected from the grid.

or i just have to measure the individual earth resistance in connected condition.

I simply put the word pit resistance and grid resistance

Pit resistance = resistance measured of individual earth pit while disconnected from grid.

Grid resistance = resistance measured of individual earth pit while connected with grid.

As i understand grid resistance is always going to be less than pit resistance.

Do any standard ask specificaly to take grid and pit resistance separately. and do they have specific limits for that.

Dear all

canany one explain what is advantege to connect earth pit in parrel and what will be the disadvantege to connct in series