AN INTERANODE FAULT PROTECTION DEVICE FOR MAGNETOHYDRODYNAMIC CHANNELS

INTERANODE ARCING IS ONE OF THE MOST FREQUENT AND DANGEROUS FAULTS IN A MAGNETOHYDRODYNAMIC (MHD) CHANNEL. IT REDUCES CHANNEL RELIABILITY AND LIMITS GENERATOR LIFETIME. THE OBJECTIVE OF THIS WORK IS TO ELIMINATE INTERANODE ARCING. WHEN AN INTERANODE VOLTAGE EXCEEDS APPROXIMATELY 50 TO 60 V,ARCING IS LIKELY TO OCCUR. THIS ARC IS DRIVEN BY THE LORENTZ FORCE INTO THE INTERANODE SPACE, WHERE IT CUTS THE INSULATOR AND ERODES THE ELECTRODES. THIS "FAULT" CONDITIONHAS A TENDENCY TO PROPAGATE UPSTREAM, ULTIMATELY CAUSING CATASTROPHIC DAMAGE. THUS, A FAST, AUTONOMOUS, PASSIVE DEVICE IS NEEDED TO ACT AS AN INTERANODE "ELECTRICAL SAFETY VALVE". THIS DEVICE WOULD CLAMP THE INTERANODE VOLTAGE AT ASAFE LEVEL. VOLTAGE CLAMPING NORMALLY IS ACCOMPLISHED BY CERAMIC DEVICES KNOWN AS SURGE ARRESTORS. THOSE THAT ARE COMMERCIALLY AVAILABLE HAVE NEITHER THE DESIRED VOLTAGE-CURRENT (V-1) CHARACTERISTIC NOR THE CAPABILITY TO ABSORB LARGE ENERGY. THESE CERAMIC DEVICES WILL BE MODIFIEDSO THAT THEY CAN MAINTAIN APPROXIMATELY 60 V INTERANODE VOLTAGE WHILE CONTINUALLY PASSING UP TO 40 A OF CURRENT. ATA VOLTAGE BELOW 40 V THE DEVICE WILL LIMIT THE CURRENT TO LESS THAN 0.1 A SO THAT, UNDER NORMAL OPERATING CONDITIONS, THE POWER LOSS IS NEGLIGIBLE. DESIGN AND CONSTRUCTION OF THE DEVICES AND BENCH-TOP TESTING USING A DC POWER SUPPLY WILL BE PERFORMED IN PHASE I. USING THE DATA OBTAINED FROM THESE TESTS, A PROTOTYPICAL DESIGN OF MHD-CAPABLE DEVICES WILL BE DEVELOPED. IN PHASE II, THE PROTOTYPES WILL BE CONSTRUCTED AND DEMONSTRATED ON THE MARK 7 MHD CHANNEL AT AVCO RESEARCH LABORATORY/TEXTRON. FOLLOWING SUCCESSFUL DEMONSTRATION ON THE MARK 7 CHANNEL, EXPANDED QUANTITY COULDBE INSTALLED ON THE COMPONENT DEVELOPMENT AND INTEGRATION FACILITY (CDIF) LONG DURATION GENERATOR.