Design of a solid-state D.C. circuit breaker for light rail transit power supply network

This paper presents the design of a d.c. fault current limiting and interrupting device for light rail transit, using IGBTs to provide current conduction and blocking. Upon detecting a short circuit fault, hysteresis control maintains the current in predefined limits. The fault current is frequently commutated to a metal oxide varistor, which absorbs the magnetic energy stored in the line. The device is designed for nominal values of 750 V, 500 A in normal operation. A prospective 60 kA fault current is limited to an average of 2 kA, to satisfy the requirement of protection. Thermal modeling shows that the IGBT junction temperature remains below the limit in both normal and fault modes, by using a heat sink with forced air cooling. The result is a recommended design for a commercial d.c. circuit breaker.