comparison between unit and non-unit system   for line protection


                                 *non-unit* 


~ no need to use pilot wire.

~ is less expensive.

~ circuit breaker on both sides have trouble tripping together.

~ the stability of the system is affected if the circuit breaker trip on both side takes longer due to have above difficulty.

~ non-directional time graded system directional time graded and distance protection are used.


                                                          *unit*

~ the use of pilot wire is required.

~ the cost is higher due to the pilot wire.

~ circuit breaker on both sides can be tripped together.

~ trips with circuit breaker on both sides so that stability of the system is not affected.

~ used circulating current system, voltage balance system and translay relay system.