Does IS limiter operates for this Scenario?

[NickParker]

Refer below sketch,

With GTG-1,2,3 running,
CB-A, CB-B, CB-C, CB-D Closed
Bus tie C closed,
For a fault a Switchgear B Bus, will the IS limiter at Switchgear A operate?

 

[Kiribanda]

Per the given SLD, since all CBs are closed, for a 3P fault shown, there is a fault current path through the IS limiter.
Since the IS limiter works by sensing di/dt of the through fault current, it is my understanding that to confirm whether it will work or not
unless a complete sc study is required.
Also if the generators are LRG or HRG then due to inherent GF fault current limitation, the IS limiter may or may not work for a GF at the same location.
Again a GF study is required.

 

[RRaghunath]

How are these generators earthed! I suppose it would either be LRG or HRG. It is also likely (going by the industry practice) that only one of the generators is earthed at any given point of time.
In any case, the current at the point of earth fault is likely to be low.
The Is limiter is meant to segregate the bus so that the fault current to be interrupted by the breakers falls well within their rated SC current.
Thus, the Is limiter is not expected to operate for above earth fault.

R Raghunath

 

[NickParker]

Sorry, my bad. I should have mentioned Phase faults (L-L, L-L-L) as there is grounding transformer directly connected to the bus.
The switchgear B do not have required short circuit capacity if the IS limiter do not blow.

 

[RRaghunath]

The Is limiters are set for a particular current.
Is the setting based on the fault current at switchgear-B or higher!!
You may like to refer Is limiter literature.

R Raghunath