Partial Discharge (PD) is one of the biggest factors that cause the breakdown of cables in both high voltage alternating current (HVAC) and high voltage direct current (HVDC). In comparison to AC insulation systems, the behavior of PD is significantly more complex in DC insulation systems, especially in HVDC Cross-linked Polyethylene (XLPE) power cables. Since PD activities are essentially a result of increased electrical stress under loaded conditions, the distribution of temperature, electrical fields, and PD inception all become large contributors to cable aging. The goal of this paper is to evaluate the PD inception voltage (PDIV) in HVDC power cables and to compare their XLPE insulation performance under high DC voltage and thermal stresses. The impact of the void's size and position on the PD inception voltage is also investigated. The correlation with the shape and the size of the voids in DC insulation system and the PD inception voltage will be found. The paper will also show how the PDIV is dependent on temperature under the investigated circumstances. This study is conducted using Finite Element Analysis (FEA) software (COMSOL Multiphysics).