Zr vacuum insulator stack is a type of electrical insulator used in high-power vacuum devices, such as vacuum interrupters and vacuum circuit breakers. It consists of a stack of zirconium oxide (ZrO2) ceramic discs, each with a metallized surface, separated by vacuum gaps. The metallized surfaces are typically made of molybdenum (Mo) or tungsten (W).

The Zr vacuum insulator stack operates on the principle of secondary electron emission. When an electrical field is applied across the stack, electrons are emitted from the cathode (negative electrode) and accelerated towards the anode (positive electrode). The high-energy electrons collide with the ZrO2 surface, causing the emission of secondary electrons from the ceramic. These secondary electrons are then accelerated back towards the cathode, creating an electron avalanche.

This avalanche of electrons leads to the formation of a plasma, which is a highly ionized gas. The plasma is characterized by a high electrical conductivity, allowing the current to flow through the vacuum gap.

The main advantages of Zr vacuum insulator stacks are their high dielectric strength, low dielectric losses, and ability to withstand high temperatures and radiation. They are widely used in high-power vacuum devices, including vacuum interrupters, vacuum circuit breakers, and vacuum switches.