MHO Transformer

[Mbrooke]

Wanted to leave off in this thread but it has since closed:

https://www.eng-tips.com/viewthread.cfm?qid=423891

In summary

Single breaker double bus station. Same for both high and low side voltages, 4 autotransformers.

The bus coupler has two MHO distance elements one looking in each direction; both set to reach at 10% of the shortest line and delayed by 8 cycles.
The transmission lines have an:


1. 80% Zone 1 set at 0 cycles
2. 125% Zone 2 at 35 cycles
3. A reverse zone 3 set at 16 cycles at 10% reach of the shortest line
4. A forward Zone 4 set at 65 cycles looking well beyond into the system.


I'm unsure what to do with the transformer's distance elements or how they will behave.


My desired outcome is that should a bus fault occur, the bus coupler will open in about 10 cycles and then all the line breakers connected to the effected bus will trip in about 18 cycles in reverse zone with re-close blocked. I'd like the transformers connected to the effected bus to do the same via step distance elements; leaving the unaffected remaining bus, lines and trafos energized.

My question is, is this scheme even possible to pull off? And if so, is it even reliable enough to consider where dedicated BB does not exist?

 

[Mbrooke]

To add, I don't want to reach through the transformer to protect the busbar, however my fear is that should the busbar fault be triggered by a failed CCVT I'd loose the MHO protection where as if I'm seeing through the transformer my voltage source will always be healthy. Then again it may not be worth the trouble.