Transmission line transformer for reliable and low-jitter triggering of a railgap switch

Abstract

The performance of railgap switch critically relies upon multichannel breakdown between the extended electrodes (rails) in order to ensure distributed current transfer along electrode length and to minimize the switch inductance. The initiation of several simultaneous arc channels along the switch length depends on the gap triggering technique and on the rate at which the electric field changes within the gap. This paper presents design, construction, and output characteristics of a coaxial cable based three-stage transmission line transformer (TLT) that is capable of initiating multichannel breakdown in a high voltage, low inductance railgap switch. In each stage three identical lengths of URM67 coaxial cables have been used in parallel and they have been wounded in separate cassettes to enhance the isolation of the output of transformer from the input. The cascaded output impedance of TLT is ~50 Ω. Along with multi-channel formation over the complete length of electrode rails, significant reduction in jitter (≤2 ns) and conduction delay (≤60 ns) has been observed by the realization of large amplitude (~80 kV), high dV/dt (~6 kV/ns) pulse produced by the indigenously developed TLT based trigger generator. The superior performance of TLT over conventional pulse transformer for railgap triggering application has been compared and demonstrated experimentally.

An experimental and numerical study: to investigate the switching characteristics of a field-distortion sparkgap switch in various SF6 admixtures

“…A reduction in t d and σ d can also be achieved through UV illumination of the discharge gap [12] and by applying a fast dV/dT trigger pulse [13]. Verma et al [14] experimentally studied the switching performance in j(SF 6 ): j(Ar) = 20:80 by applying a trigger pulse of slew rate ∼0.07 k V ns −1 , 6 kV ns −1 , and reported that by applying a trigger pulse with high dV/dT the t d and σ d were improved. (Where 'dV/dT' implies to rate of rise of trigger voltage with time (T)).…”