Technology: Earth wire in transmission line।step and touch potential

Earth wire Or ground wire in transmission lines:

Touch potential:

Conductors are not directly connected to the transmission tower. They are connected to tower by means of insulators. If overhead power lines are not properly insulated or insulation breakdown happened , the current will flow towards the ground through the towers .If someone accidentally touch the tower whole current will flow towards ground through his body which is very dangerous.

Hence, Earth wire is connected to peak of the tower which has zero potential and the unwanted current present in tower flows through ground wire . Hence one can get protection against touch potential (shock due to touching electrical wires )

Protection from Lightening:

Ground wire is placed at topmost position (at peak) so that it can also provides protection against lightening. Ground wire has zero potential . Other conductors (except ground wire) have some potential let say it is 33 kV line. The typical voltage of lightening is 300 million V. As potential difference between ground wire and lightening is greater than 33kV conductor , lightening prefers high potential difference path I.e. it travels through ground wire. Hence ,line conductors are protected by using the ground wire.

Step potential :

Due to earth wire touch potential is minimised ,but step potential cannot be minimised by Earth wire . Step potential (when we steps our feet we may fell high voltage shock ) happen when accidentaly conductor cuts and falls on the ground . The voltage is distributed over the ground. Near the conductor there is high voltage . And as we moves away from the conductor voltage decreases.

Consider ,

A place near to the conductor ( say at 10 cm) have voltage 33 kV , and at 20 cm it is decreased to 30 kV .

If one kept his one foot at 10 cm and another at 20 cm , due to difference of 3 kV voltage ( we know current flows if there is voltage difference) person may get shock.

To avoid this one should stand with feet near to each other without keeping any space between them. And like astronaut one have to jump and escape to the safe place.