Line differential Protection can be applied on overhead lines and cables. It is a very reliable unit protection. All faults on the line, between the line CTs, are cleared instantaneously. It has ability to detect high resistive earth faults It is a preferred protection scheme for underground cable and also for short lines where Distance protection would have limitations.
Due to its factor of reliability, it is used as an additional fault detecting relay for short line protection by most of the State Transmission Utilities as well as the Central Transmission Utility. It is also used as fault detecting protection in case of Hybrid line configuration comprising of Overhead lines and underground cables.
Line Differential protection is usually applied as Primary protection as it is instantaneous and not coordinated with any other Protection. However, in the modern line Differential protection. IED may also have Distance protection and over current protection that is coordinated as back up protection.
Line Differential Relay, Line Capacitances & Fiber-Optic Communication link
