AC line protection operating conditions in the near vicinity of HVDC installations

HVDC transmission systems have historically been connected to AC networks with high short-circuit power. This has meant that the AC line protection has hardly been influenced by the HVDC transmission. With the increased use of static VAr compensators and trend towards high power transmission levels for HVDC systems, the AC system is no longer always strong in relation to HVDC transmission. As a result, the possible influence of HVDC transmission on AC line protection has to be considered. Two risk factors for improper AC line protection operation are defined by the author as well as the influence these have on different types of line protections