Preliminary results from the multishot opening switch and barrel testing at ARDC

The General Electric (GE) Multishot Switch and Barrel have been designed and assembled, and preliminary testing has been carried out at the Armament Research and Development Center (ARDC) at Dover, NJ. The Electromagnetic Launcher System incorporates an existing homopolar generator, storage inductor, and range tank with the GE switch and barrel into a Multishot Facility capable of three 500 kA shots at a rate of 4 Hz. Preliminary low current (∼250 kA) single shot tests of the system indicate that the Multishot injector, data acquisition and control systems, and shot timing meet design objectives and that the switch does commutate effectively into a moving armature at an arc voltage of 335 volts. Five single shot tests have been performed on the system. In these tests the switch brush has experienced difficulty in carrying full charge current (>300 kA) in the opening segment of the switch. Static measurement of contact voltage on the stationary brush at 60 Hz, 450 kA has eliminated contact resistance runaway as a possible cause of this difficulty. Deflection measurement in situ at ARDC, using 300 kA in a short circuit test and 3-D finite element analysis of the magnetic force on the brush suggest a possible loss of contact between brush fingers and switch rail surfaces, particularly in the periphery of the input bus. Increased compliance is being built into the brush and the switch assembly is being widened to accommodate the wider brush. Full power switch testing is underway to evaluate the effectiveness of these design changes, and Multishot testing is scheduled to resume when the ARDC facility again becomes available. The Multishot Electromaqnetic Gun Program was developed under Air force Armament Laboratory sponsorship.