Over the years, high voltage transmission of large energy blocks over long distances has widely developed from the Line Commutated Converter (LCC) technology. However, the continuous expansion of the AC network and the increase in renewable energy penetration leads to the weakening of Electric Power Systems (EPS), causing operational problems for the LCC-HVDC. This paper evaluates the degree of contribution of the VSC-HVDC on the LCC-HVDC dynamic performance when the infeed is in a hybrid multi-infeed HVDC system. Through a steady-state mathematical framework, the new concept of Hybrid Power Voltage Interaction Factor ($\mathit{h}$PVIF) is proposed to assess the transient stability improvement of LCC. Additionally, this article introduces two key contributions from $\mathit{h}$PVIF: the complementary Improved Commutation Failure Immunity Index ($\mathit{i}$CFII), as a measure of the effective short circuit enhancement, as well as the apparent line length, which emulates the line lengths adjusting the power dispatch in the VSC-HVDC. PSCAD/EMTDC^TM time-domain dynamic simulations are performed to assess the indexes, and the Matlab${}^{\circledR }$ software will be used to assist in mathematical operations.

This article addresses the study regarding the emergence of ferroresonance and selfexcitation phenomena in Subsea Power Systems - SPS, composed essentially of synchronous generators installed on a platform (Topside), a three-phase umbilical cable and the electrical loads, the latter constituted by induction machines located on the seabed and connected to the umbilical through a power transformer and power electronic converters. Such phenomena are conceptually stated and characterized in the scope of SPS and the simulations are carried out in the PSCAD/EMTDC software, in its parallel processing environment, to verify indications of the existence of problems in the base network of the subsea distribution system.