Regulated high-voltage power supplies (RHVPSs) have been developed at Institute for Plasma Research and utilized for neutral beam and radio-frequency heating applications of the steady-state superconducting tokamak (SST-1) up to 80-kV, 130-A rating. They were developed in-house and are being delivered to different research institutes for various applications.

The RHVPS delivers power to various loads at the megawatt level. These loads have very low fault energy tolerance; therefore, fault protection is mandatory. In addition to this, at each stage of the power transformation/conversion, a special diagnosis is necessary to protect the power supply components. Also, the output fault protection has to be done in such a manner that fault energy is not more than 10 J. In fault conditions, the output has to be turned off within 2 s. Having these requirements, an output fault-protection system has been developed with suitable sensors and to manage fast turn off, choosing appropriate components.

The multiple-secondary transformers (two of them, each at a 5.6 MVA rating with 40 outputs) are used at the front end of the RHVPS. They may become damaged for overload at any one of their secondaries, while remaining secondaries carry much less current or no current. Such a localized overload is not sufficient for tripping the main circuit breaker, whose tripping level is set to an actual overload of the transformer. A special technique is applied to sense and diagnose this fault in addition to routine overload sensing. Differentiation of such a typical fault from a real overload condition is done by sensing and monitoring the primary current of the transformer with reference to different operating scenarios. Electronic means are used for fast detection and isolation of the RHVPS from the utility supply. The presented system effectively protects the transformer from fault at any one of its 40 secondaries and in an actual overload situation.

This paper describes an overall RHVPS power scheme along with output fault protection and an internal fault diagnosis system and test results thereof.