In recent years

the enlargement phenomenon of 50 Hz harmonic current on DC line caused by energization of unloaded transformer is exposed on HVDC projects in field. To solve the problem above

a 50 Hz harmonic amplification evaluation method based on DC line parameters is proposed. Firstly

the calculation method of 50 Hz parameters for the long distance HVDC transmission line is derived. Secondly

50 Hz parameters of DC lines in a certain DC project are calculated. Then the essential reason and the extreme point of harmonic amplification are analyzed based on the results

furthermore

the index for evaluating DC harmonic amplification level is proposed. Finally

the correctness of the method proposed is verified by EMTDC simulation results

and the method is applied to the harmonic evaluation of an actual project. The results show that the evaluation results obtained by the proposed method are consistent with the practical project. Both the methods proposed to calculate harmonic amplification extreme points and evaluate DC harmonic level are independent with the detailed DC model and EMTDC simulation.