Based on the impedance constraints

a new method is proposed to trace the main harmonic source at the point of common coupling(PCC). According to the inherent features of utility and customer impedances and combining with the recorded harmonic voltages and currents at PCC

the vector projection technique is used for judging the main harmonic source of the utility side. Also

the strict inequality constraints are applied to determine the main harmonic source of the customer side. Besides

as for the more complex conditions where the properties of the utility and customer impedances are different

the main harmonic source is traced by the cosine law of geometry and strict inequality. Based on the magnitude and phasor relations of harmonic sources on the two sides

the impedance constraints are worked out. Furthermore

the confidence interval is employed to remove the abnormal monitoring data. The harmonic traceability calculation of multi-scene measured data demonstrates the validity of the proposed method. This work is supported by National Natural Science Foundation of China(No. 51477105)and State Grid Corporation of China.