Protection 40 Km 115 KV parallel lines, unidirectional power flow.

[janavax]

I'm on project that includes the protection of 115KV/34.5KV-13.8 KV substation, the corresponding inputs lines and the expansion of the source substation. The substation layout consists on two 115KV input lines arriving to a bus via circuit breakers (H type substation). The 115KV busbar has a normally open sectionalizing switch. From the bus, there are a 115/34.5 transformer at one side and two 115/13.8 at the other side. All the transformers have CB on HV and LV side. The input lines are in parallel, coming from the same substation, located 40 Km away, so the power in the line will flow unidirectional.
My questions are specifically regarding to line protection. For primary protection Line differential is going to be used, as the lines includes OPGW so data communication will be available. For secondary protection I'm not sure what to recommend:
1.- Does it have sense to use distance (21) protection on the remote side, and just overcurrent on the local side?.
2.- Another option could be overcurrent with detection of high-impedance faults (such as downed conductor) detection on the remote side, and just overcurrent on the local side?.
Thanks in advance for any advice.

 

[davidbeach]

If that sectionalizing switch can ever be closed with both lines in service, then you should do your settings with it closed; thus distance all around. If it can never be closed with both lines (interlocked) then there's not much of a need for lineward looking protection at the new substation. The differential is fine, allows instantaneous tripping all the way up to the bus without overreaching it, but with no source behind the relays there's not much more for them to do.