Touch potential and Step potential 

Touch potential and Step potential are very dangerous for human being or any live animal. The human body may get electric shocks from touch potential and step potentials. This is a very important thing for the transmission line workers so that there for continuous monitoring is very important along with an alarm system so that it warns if there is any dangerous voltage is present.

What is Touch potential and Step potential:-

Touch potential:- 

Touch potential means it is the voltage (potential) between an energized thing and the feet of a person in contact with that object. The touch potential is nearly the full voltage across the grounded item if that item is grounded at a remote point from where the person is in contact with it.

Step potential:-

 Step potential is defined as it is equal to the difference in voltage between two points at different distances from the energized item. If the fault is accure then the person could be in danger of injury by standing near to the item that has an electrical charge.

Touch potential and Step potential 

It is very important and necessary to calculate the touch voltage and step voltage. whenever the high voltage substations are designed there should proper step voltage and touch voltage calculated in specified standard.

By applying an extensive insulating layer on the earth's surface we can limit the touch voltage. The soil resistivity is different in different seasons so that is difficult to limit the step potential and touch potential. While designing an air-insulated switchgear (AIS) indoor substation,gas-insulated switchgear (GIS)  indoor substation the step voltage calculation and touch voltage calculation are very important.

We have to understand that because of electromagnetic coupling the dangerous step potentials and touch potential can present on the non-energized lines, and it is a very dangerous thing for a person who works daily on the transmission lines for maintenance and for another purpose.

If there is any dangerous voltage is present and any worker is sent for maintenance it is very dangerous so that continuous monitoring is very important with alarms so that if any dangerous voltage is present the alarm should warn the person.

The magnitude of Touch potential and Step potential depends on the following points:-

1) fault current value

2) Upper and lower resistivity of soil

3) Grid area 

When short-circuit current flows from grounding electrodes of substation and power lines the step potential and touch potential occur.

Touch and step potential calculation:-

Touch potential and Step potential formula 

E touch = [1000 + 1.5 C(s) ρ(s) ] (0.116/√ t(s)) volts 

where,

t(s) = Fault duration in sec

ρ(s) = surface layer resistivity in Ω mtr

       = 3000 Ω mtr for crushed stone layer

C(s) = 1-a[(1-ρ / ρ(s) / (2h(s)+a)]

C(s) = 1 when no protective surface layer is used 

where ,

a = 0.0106 mt

E touch = [1000 + 6ｘC(s) ｘ ρ(s) ] (0.116/√ t(s))

where 

ρ(s) = resistivity of surface layer = 3000 Ω mtr if crused stone is used 

 The limits of the step potential and the touch potential in different seasons are as shown below table:-

Touch potential and Step potential 

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