رابط لطريقة حساب مقاومة التأريض لالكترود واحد او مجموعة الكترودات

[بلعيد العزومي]

http://electrical-engineering-portal...d-pipes-part-1
والسلام عليكم

[بلعيد العزومي]

1. Calculate numbers of pipe earthing

A. Earthing resistance and number of rods for isolated earth pit
(without buried earthing strip)

The earth resistance of single rod or pipe electrode is calculated as per BS 7430:
R=ρ/2×3.14xL (loge (8xL/d)-1)
Where:
ρ = Resistivity of soil (Ω meter),
L = Length of electrode (meter),
D = Diameter of electrode (meter)
Example:

Calculate isolated earthing rod resistance. The earthing rod is 4 meter long and having 12.2mm diameter, soil resistivity 500 Ω meter.
R=500/ (2×3.14×4) x (Loge (8×4/0.0125)-1) =156.19 Ω.
The earth resistance of single rod or pipe electrode is calculated as per IS 3040:
R=100xρ/2×3.14xL (loge(4xL/d))
Where:
ρ = Resistivity of soil (Ω meter),
L = Length of electrode (cm),
D = Diameter of electrode (cm)

[بلعيد العزومي]

C. Total earthing resistance and number of electrode for group
(parallel)

In cases where a single electrode is not sufficient to provide the desired earth resistance, more than one electrode shall be used. The separation of the electrodes shall be about 4 m. The combined resistance of parallel electrodes is a complex function of several factors, such as the number and configuration of electrode the array.
The total resistance of group of electrodes in different configurations as per BS 7430:
Ra=R (1+λa/n) where a=ρ/2X3.14xRxS
Where:
S = Distance between adjustment rod (meter),
λ = Factor given in table below,
n = Number of electrodes,
ρ = Resistivity of soil (Ω meter),
R = Resistance of single rod in isolation (Ω)

Factors for parallel electrodes in line (BS 7430)
Number of electrodes (n)	Factor (λ)
2	1.0
3	1.66
4	2.15
5	2.54
6	2.87
7	3.15
8	3.39
9	3.61
10	3.8