A Low-Cost Thyristor Fuse

Thermal fuses are the devices most commonly used for effective equipment protection against fault currents within solid-state power systems. Original equipment cost versus additional expenditures for protective devices warrants elaborate means for safeguarding the investment while maintaining cost effectiveness. This has resulted in a vast variety of individually high-priced specialty fuses. Experience indicates that a large number of thyristor current-limiting fuses must be expended during the design phase of solid-state power conversion equipment so as to properly investigate converter circuit malfunctions due to nonrecurrent circuit transients. Thermal fatigue of fuses during field use necessitates a considerable logistic support in order to sustain the bulk of multifused complex power converters. This large demand cannot be satisfied at all times due to the limited number of prime suppliers, and due to the range of size, bulk, and price of present thermal thyristor fuses. Thermal analysis and extensive testing furnishes strong evidence that the desirable low-cost thyristor fuse link is feasible. This low-cost item is well-suited to protect thyristors against catastrophic failures within the constraints of any thermal fuse. Since the fuse is renewable, it compares favorably with presently used commercial thyristor fuses in terms of bulk and potential cost savings as well as in its flexible simplified rating mechanisms.