69kV Line protection 4

[edfilho78]

We are developing a protection requirement to a power line of 69kV. This line is about 7 kilometer. Because of costs we use 50/51 protection and 67N to backup protection. Is this scheme efficient??? What are the disadvantages of it?

Thanks

Ed

 

[Eleceng01]

edfilho78, can you please supply more information? Is the line radial (i.e. generation only at one end of the line)?

 

[edfilho78]

Dear Eleceng01

The line is radial and there is a parallel line. One of the end is a generation and i don't have information about the other end.

Thanks

 

[Eleceng01]

If the line is truly radial, then there are no real disadvantages of using 50/51 relays. For the 67N, you might want to look at magnetic coupling between the lines if they are parallel.

Hope this helps.

 

[JMatt]

Sometimes 51 relays can miscoordinate with distance relaying. Be sure to do a coordination study with the protective devices feeding this 69kV line.

 

[Eleceng01]

Good point JMatt! I forgot to mention coordinating with upstream devices.

 

[slavag]

Hello.
I would like add several points.
Standard solution in this case is 50/51, but don't forget:
On the second side( w/o generation) we must install
directional overcurrent 67 with time delay about 0.2-0.5sec.

If we use 67N as back-up protection, we also must install on other side 67N with reverse direction ( time setting lower then 67N on generation side).

Please see attached scheme:

Regards.
Slava