Problems with tap-changing power supplies

To meet conflicting requirements for low ripple, high stability, wide bandwidth, high efficiency, and low radiated electromagnetic interference, a synchrotron dipole power supply was built with an SCR (silicon-controlled rectifier) tap-switched primary isolation transformer and linear bipolar transistor passbank. Numerous operational problems encountered after delivery and installation have necessitated a major overhaul of many of the supply´s systems to meet full accelerator design goals. The author describes progress in overcoming limitations of the supply; typically, only one upgrade at a time was installed due to the tight running schedule. Particular emphasis is paid to the technique for switching taps on-the-fly for reliable operation.<>