Evaluation of the effectiveness of shielding and filtering of HVDC converter stations

The application of the Numerical Electromagnetic Code (NEC) to the problem of EMI (electromagnetic interference) from HVDC (high-voltage direct current) converter stations is investigated, with particular emphasis on evaluating the effectiveness of valve hall shielding and filtering. It is shown that valve hall shielding alone is not effective in reducing the EMI of converter stations. Appropriate combinations of shielding and filtering produce EMI attenuation of the order of 20 to 30 dB. In order to reduce the EMI, the length of busbars and other connecting elements should be reduced to a minimum, both inside and outside valve halls. The location of filters should be chosen to minimize the length of high-frequency return-current paths