The large-capacity static var compensator (SVC) is applied in actual projects. Theoretical analysis and simulation results show that

a large amount of 3

5 and other odd harmonic currents will be injected into the fault-point from the SVC equipment when faults occur on the low-voltage side of the transformer. What is more

the harmonic current is significant in content and slow in attenuation rate. Traditional transformer differential protection usually adopts harmonic blocking methods to prevent incorrect operation from current transformer saturation at external faults

magnetizing inrush current and over-excitation. Harmonic currents produced by the large-capacity SVC equipment may make the harmonic blocking element make a wrong judgment

leading to slow operation of the differential protection or even failure to operate. To solve this problem

the 2nd harmonic rather than 3rd harmonic should be used in TA saturation criterion. Digital simulation test is performed to verify the validity of theoretical analysis.