Review protection of transmission line  


~ types of protection 

1) over current protection

~ time graded or current graded

~ directional or non directional

2) earth flute protection 

3) pilot wire differential protection

4) carrier current protection

                                  ~use~

1) over current protection : for the main protection of the distribution line and for the back up protection of the main line of the main protection is of the distance type

inverse definite minimum time relay for time graded system is used for time graded system and instantaneous type relay is used for the cost graded system

2) earth flute protection : in addition to phase fault protection different means flute protection is required. faster than over current protection.

3) pilot wire differential protection : for protection of important line of short length ( some kilometer) 

4) carrier current protection : when line length is high and where circuit breakers on both sides have to be operated simultaneously are used.