The value of adopting extra-high voltages (EHV) and ultra-high voltages (UHV) for bulk power transmission lines in being able to achieve very high levels of availability. This is particularly the case at UHV and requires a fundamental philosophy of dependability right from the conceptual stage. This notion is discussed and related to reliability-centered maintenance (RCM). Switchgear failure modes and rates are reviewed as applicable and on line condition monitoring with a view to achieving predictive (condition-based) maintenance
