Earthing Grid

For any earthing installation within India,please comply with the provisions given in the Indian Standard,IS:3043

That is OK. But how to start designing the earthing grid. will anybody let me know

Rajiv Mehan

Sir The earthing system shall be designed after considering the following minimum aspects: 1)electrical network of yr plant. 2)Soil resistivity. 3)System fault current. Pleez refer to IEEE-80 for detailed step wise calculations for the same,where in the procedure to derive allowable step and touch potentials is available. The formulae used are empirical in nature and best to refer rather than to keep them on the finger tips. From this u will be able to arrive at the BOM for the earthing material (below ground). Hope i am able to throw some light on the issue. But u should glance thru IS if it is to be installed in India. regards ravipra01

thanks Ravi

Rajiv Mehan

Rajiv:

For any earthing study, informations that are needed are as folllows.

(1) Soil resistivity details. Normally you won't have uniform soil, but if you can carry out soil resistivity study and map a grid map of the soil resistivity, it will help. ANy construction already done will affect the virgin soil's resistivity.

(2) Next you do need to carry out short circuit study and find out what you maximum short circuit values for both single line fault and three phase faults are. You also need to determine if the contribution from the electric uitlity andr from your internal source and know which is a greater contributer.

(3) Third you need to lay the plant layout and check where are the possible locations of this maximum fault.

(4) Taking the soil resistivity and the fault current into consideration, you need to calculate the maximum step voltage ( voltage between your two legs when this fault current is flowing), touch voltage ( Voltage between a mettallic structure touched by your hand and your leg) and reach touch voltage (when you are standing in the plant and touching a pipeline which is grounded externally which is at zero potential).

(5) Next you need to calculate the permissable step voltage, touch voltage and recah touch voltage .

(6) Next if the step voltage, touch voltage and reach touch voltage are higher than the permissable values, you need to design a ground mat so that the soil resistivity is modified so that these values are within limits. You can also then lay stones which would reduce the step, touch and reach touch voltages.

(7) If you company can afford it, buy the sofware from this company (http://www.sestech.com/). The program enables one to carry out these functions by the program.

I don't work for this company, I have ony used it. It is good.

Good luck.

George

Thanks Mr george for the detailed design guidelines

Rajiv Mehan

Thank you Mr Rajiv for enabling a discussion, on such an important topic,through this forum CR4. The detailed design guidelines provided by Mr George are very useful.

Thanks Mr Mani, for the followup of the discussion. Infact I learnt many new facts which i missed during design of earthing system. Thanks everybody for participation in the discussion

Rajiv Mehan

India