Hi Mr Raghunath
Unlike earth fault, phase to phase fault, etc., inter turn faults are difficult to detect due to their localized nature. Normally, these turn faults eventually turn into earth fault puncturing ground wall insulation or phase to phase to fault in end winding and EF/differential will pick it up.
In large 2 pole generators, the stator winding is mostly of single turn Roebel bars and hence the concept of inter turn insulation failure does not apply here. Multi turn diamond coils are more in common in multipolar hydro generators. In those cases, I have seen what is called cross differential protection being used to detect turn faults, which of course adds to the cost of the protection. Here, the stator winding is usually split into two halves with each half having its own identical CT and their secondaries are cross connected to detect tun faults. (Of course, for still better detection & protection, you can split the winding into more parallel paths with each section with its own set of CT's but that would be still additional cost driver.)
The schematic of cross differential for interturn protection.
Hope I have answered your question (of why it is not being included now a days), which, thanks to bean counters, boils down to additional cost justification for the interturn protection but I would consider it a critical protection to be included in the project design stage.
Muthu
