Telephone interference criteria for HVDC transmission lines

The coupling between a transmission line and telephone cables is calculated on a general basis. Based on field measurements of the current harmonic spectrum from a modern 12-pulse HVDC (high-voltage direct current) converter, the ratio between disturbance current and resulting noise level in a telephone system is established. Disturbance current limitation criteria are identified based on tolerable noise level and assumptions regarding typical worst-case coupling conditions in a suburban area between a transmission line and a telephone system. It is concluded that disturbance current criteria as currently specified for some HVDC lines are substantially more stringent than corresponding criteria for both distribution lines and HVAC (high-voltage alternating current) lines