Sample value differential protection has the advantage of being capable of making the differential protection characteristic work by directly using the instantaneous sample value

which requires less calculation and operation time

but it has the disadvantage of easily being affected by interference and its reliability should be studied. In order to solve this problem

an algorithm based on virtual current for bus-bar protection is proposed based on the research achievement in the sample value differential protection. By merging the sampling values of the branch fault component currents of the bus-bar of the same moment and in the same direction

the bus-bar system is simplified into two virtual currents. Based on the waveform differential attribute of the virtual currents in different bus-bar operating modes

the differences are quantitatively analyzed using the correlation analytic technique. By calculating the correlation coefficients of sampled current values and utilizing their distribution characteristics

the external and internal faults can be correctly distinguished. Results of theoretical analysis and simulation have proved that the proposed criterion is capable of rapidly and reliably distinguishing internal fault from external fault

while insensitive to current transformer (TA) saturation to a definite extent. This work is supported by National Key Technologies R&D Program (No. 2012BAA15G00).