A Comprehensive Design of the Thyristor-Based Crowbar for Vacuum Tube High-Voltage DC Power Supplies

Abstract

High-voltage power supplies (HVPSs) are widely used to drive vacuum tubes, inherently susceptible to vacuum arc faults. Owing to the considerable cost of vacuum tubes, the HVPS should enjoy a reliable, fast protection mechanism. A common protection mechanism against vacuum arc faults is the shunt crowbar. The crowbar diverts the energy stored in the elements of the HVPS through itself as a parallel path, thereby protecting vacuum tubes from irrecoverable damages. Among all types of the shunt crowbar, the thyristor-based crowbar along with the fault current limiter (FCL) resistors attracts more attention because of its more reliable operation. The absence of the comprehensive design procedure providing an insight into selecting the key components of the crowbar is strongly felt. This article presents a comprehensive design procedure for selecting these components. All constraints which should be satisfied by the protection mechanism and key components are elaborated. By doing so, the upper and lower limits of the FCL resistors, the thyristor specifications, and their series inductance are specified. It is shown that thyristors with high nominal peak current cannot contribute to the operation of the crowbar. The intersection area of the constraints and optimum values are determined for one case study. The simulations and experimental tests are exploited to evaluate the effectiveness of the presented design procedure.