Bus Zone Protection On Open Conductor Site

[isquaredr]

High impeadance bus zone protection with 3-ct's connected in parallel for each feeder feeding onto buswires with a high impeadance relay across is what I am use to seeing for this type of protection in metal clad switchgear. The other day whilst on an open conductor site I noticed 2 out of the 3 ct's per feeder were in parallel the 3rd was connected in reverse, they again supplied buswires with a high impeadance relay in circuit. I asked around for an explanation for the reversed ct, the only explanation being it allows the scheme to protect against phase - phase as well as earth faults.
My question is how?

 

[isquaredr]

Slavag
Hope I am correct with this.
So lets say A-phase ct i= -1 (reverse connected), B-phase ct i=1 (normal connected)& C-phase ct i=2 (normal connected, half ratio)
for the following bus bar faults the current in the relay (i) would be:-
A-E, i=-1
B-E, i=1
C-E, i=2

A-B, i=2
A-C, i=3
B-C, i=1
A-B-C, i=2.6
All other faults out of zone will have a cancelling out effect rendering the scheme stable.

 

[slavag]

Yes.
You are correct.
A-E, i=1 ( "-" is not important).
Lets go check phase to phase to ground/earth faults.
AB-E, i=0, still problem.
BC-E, i=3, passed.
AC-E, i=1, passed.
ABC-E, i=2.6, passed.
Something missing???
Check again.
Regards.
Slava.
Crazy, how time we spent for understand old scheme, but it's intresting.