High voltage direct current (HVDC) is today recognized as an effective and efficient means of transmitting bulk power over long distances through over head lines or cables. The reliability of HVDC links have always been of primary concern in planning and operating of power systems. The existence of spares and maintenance practices do affect the availability of HVDC stations. The HVDC converter transformer plays a relevant roll in HVDC converter station, not only due to the direct cost associated to them but also causes its availability affects the HVDC transmission capability (or) capacity. In this paper the effect of converter transformer failure rate, repair time on expected capacity level of three phase three winding converter transformer with and without spares is analyzed and compared. It also effect of number of spares on expected capacity level is presented. Key words: HVDC transmission system, converter transformer, unavailability, Morkov modeling.