Reliability of the TJ-II Power Supply System: collection and analysis of the operational experience data

An effort to develop a fusion specific component reliability database is being carried out by international organizations such as EURATOM and the International Energy Agency (IAE). Moreover, several fusion related devices are involved in the collection of operational experience. In this frame, TJ-II is performing a reliability assessment of its main systems initiating the evaluation process with the Power Supply System (PSS). The PSS has been chosen because it is one of the most critical systems in TJ-II. During a TJ-II pulse, the provision of magnetic fields requires a total amount of power of almost 50 MW. Such amount of power is supplied by the national grid and a 140 MVA flywheel generator (100 MJ, 15 kV 100 Hz). Since the TJ-II loads require direct current, a set of thyristor converters, transformers and circuit breakers for each coil system are being used. Power requirements range from 5 kA (100 V) to 32 kA (1000 V). Also the heating systems (ECRH and NBI) load the PSS with additional 15 MVA. Failure data of these main components and components from auxiliary systems (rectifiers cooling, uninterrupted power supply system, control system ...) have been collected from PSS operation notes and personnel interviewing. Data related to general operation, campaign schedules, and maintenance have been collected from TJ-II engineering annotations, TJ-II web based electronic-board and TJ-II campaign archives. A database with date, time, pulse number, failure description, failure mode and other related information has been implemented. Failures and malfunctions in the PSS have been identified and processed, including information on failure modes and, where possible, causes of the failures. About 1700 failures and malfunctions have been identified in the period May 1998 - Dec 2004 (1309 of them in operational days and 381 during tests or maintenance task). Most malfunctions come from spurious signals over the circuit breaker and from the generation system. Main statistical values, such as availability of the PSS for different modes of function, failure rates of subsystems and components, corresponding standard errors and confidence intervals are being calculated and will be useful for the International Fusion Component Failure Rate Database (FCFR-DB). A reduction of annual failures, as well as an increasing of the PSS availability and reliability ratios from 1998 until now, has also become evident from the interim analyses. (author)