Insulator Technologies to Achieve Maximum Electric Field Holdoff

In large machines, such as accelerators and high power microwave systems, it is common to implement pulsed power technology. Pulsed power attempts to deliver large amounts of power in a short amount of time. This is done by storing high voltage and delivering that energy to the desired load quickly through switches. To ensure that the energy is delivered to the desired load it is necessary to use insulators to separate conductors having different potentials. The insulators function is crucial in the success or failure of the system and because of this, much research has been done in the materials, geometries, and sizes of insulators. A common mean of failure for these insulators is surface flashover. Surface flashover occurs when the electric field becomes strong enough to accelerate electrons along the surface of the insulator to a point where an arc is created between conductors of different potentials. The machine is therefore limited to the amount of voltage it can sustain and the amount of power it can deliver. By making modifications to the insulator, improvements in sustained electric field has been documented. This paper attempts to further investigate the different methods used to increase the sustained electric field to improve the function of the system.

I. Introduction

In pulsed power systems it is necessary to use insulating materials to separate conductors having different potentials. These insulators can be made from many different materials and can have varying geometries. This variability is done in order to increase how much electric field the insulator can tolerate before succumbing to surface flashover or breakdown through the bulk. Also called the sustained electric field of the insulator. Pulsed power systems commonly fail due to surface flashover along the surface of the insulator. Improving insulator technology will lead to higher voltage capability and more reliability in experimentation. To investigate what modifications can increase sustained electric field, it is beneficial to understand how surface flashover occurs. Secondary electron emission avalanche (SEEA) is a dominant theory of how surface flashover forms [1]. SEEA is the theory that electrons emitted at the cathode triple point are accelerated by the potential and collide with the surface of the insulator. The energy from the impact releases more electrons from the insulator's surface. These recently freed electrons are then accelerated by the potential until they also collide with the surface of the insulator releasing even more electrons. This effect accumulates until a current path, via the electrons along the surface, is formed. Minimizing the avalanche could improve the maximum sustained field achieved by the insulator.