  Due to generation retirements and growth of renewable energy sources
integration, there will be widespread changes in the real and reactive power
flow in nowadays power systems. These changes also bring about challenges on
system operation and stability. High voltage direct current (HVDC) technology
seems to be a promising solution to these new challenges. A study on the impact
of the replacement of 500KV AC transmission lines by VSC-HVDC transmission line
on system voltage security is conducted. The analysis is based on reactive load
margin method and implemented on one of the Dominion Energy planning models.
Different control schemes of HVDC are considered. Using k-means clustering
method, three representative zones within the network are selected. The results
corresponding to them are demonstrated and discussed. It is shown that HVDC
lines with P-V control remarkably improve system voltage security, while those
with P-PF control scheme have negative effects.
