distance protection for cables

[144x]

Hi ,
let's assume that we have a 66KV power cable with 500 sqmm
cross section with the approximate lenght of 4 km.can we
use distance relay for the protection of this line or should
we use other means of protection?
thanks.

 

[peterb]

Cable circuits are usually protected by a phase comparison or a pilot wire type scheme, both of which require communication between the line ends.
Distance protection MAY be used, providing the setting range available will accommodate the secondary impedance of the cable - note that the impedance angle will be generally lower than for for overhead line circuits. If communication is avalable, a permissive overreaching transfer trip (POTT) scheme may be preferable to give enhanced coverage & improved speed - the need for this will depend on the critical clearing time of the line.