CT

The knee volt in a ct is where the CT windings saturate.. The test can be performed with a voltage supply (0-250V) with rheostat, and a multimeter placed in series with one of the leads and set to amps.

Connect you power supply to x1 & x2 of CT and begin injecting voltage in steps of ten volts, while documenting current reading. The point in where the current reading becomes non-linear is your knee point.

The CT should be labeled C50, C100, C200, etc.. Those numbers reflect where your kneepoint should be in test..

The kneepoint reflects the amount of voltage the CT will be able to produce at 20 times normal current. If the CT is not sized properly it will saturate under fault causing protective relay to not see current therefore not operating.

As far as multicore (tap) CT I do not believe the tap setting will effect kneepoint, but am not 100% positive. Perform saturation test at all taps and you will know for sure..

1- CT's knee point voltage relate to it's rated volt-ampere, rated secondary current, rated secondary resistance and rated accuracy limit factor.

Uk=ACF x ( VA/In+Rct x In )

2- In multi secondary winding (tap) current transformers (please don't say multi core) higher knee point voltage is related to higher tap.

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