Accelerated life testing of a traction inverter

The introduction of new technology into equipment brings with it the risk of long-term reliability problems. Manufacturers need to review methods of type testing to reflect the changing properties of inverter technology. The introduction of a traction drive using insulated gate bipolar transistor semiconductor switches to trains for the Northern Line of London Underground represented such a change in technology. The failure of IGBTs under conditions of deep thermal cycling is well documented and it was uncertain as to whether the stresses of station-to-station running would give rise to such a problem, so a life test was devised.