Knee point voltage is the current transformer's saturation limit multiplied by a factor of 10. Each protection class CT must be used in the non-saturation mode. As a result, we must determine the maximum allowed voltage limit that can be applied to the current transformer's secondary winding. The Knee Point Voltage of a Current Transformer is defined by the IEC as the voltage at which a 10% increase in CT secondary voltage results in a 50% increase in secondary current.