Surges in Overhead lines

Surges in overhead lines affect substation equipments, can cause backflashovers and can affect power quality.

Surges in overhead lines can be categorized into two types
  1. Internal Surges and
  2. External Surges
Internal Surges are surges caused due to switching of capacitors, earth faults, sudden load swings, etc.  External Surges are caused due to lightning strikes on power lines.

There are two methods of protecting Transmission lines from surges. 

  1. Shielding Methods and
  2. Discharge Methods

Shielding methods use a shielding line run along the top of the tower to shield the lines from lightning.  The shielding line offers protection up to an angle of 30 degrees from the vertical on either side.  Sometimes two shielding lines are run in parallel to increase the area under protection. 

The other method of protection is the discharge method of protection.  The discharge method of protection uses surge arrestors which discharge the surge through themselves.  These arrestors are mostly non-linear resistors or spark gap based arrestors