Novel differential protection with double resteraint coefficient

To overcome the shortcoming of the common method, which analyzes the differential protection characteristic in the differential currents vs. resistant currents plane, a novel method is proposed according to the relative relationships about the amplitude and the phase between the two side currents. After contrastive investigation of some customarily differential protection schemes, the universal mathematics expression about differential protections is drawn out. Then some discussions on the impact about the TA saturation on the differential and resistant current are given out. According to the universal expression, a perfect non-linear resistant criterion with double resistant coefficient is presented. Due to the mechanism of the differential imbalance current in external faults, this new criterion auto-regulates the resistant coefficient by the amplitude-phase relationship between the two side currents. This novel criterion provides a novel means of how to get a good and spread use of the non-linear resistant differential protection in field.