Electricity is the flow of electrons from higher-voltage potential to lower-voltage potential. Passing through the atmosphere, electrical failure occurs when the voltage exceeds the dielectric strength of air, which happens to be a mere 3kV/mm.
Air is a poor conductor of electricity, which is why MPF constructs a variety of vacuum electrical feedthroughs for anywhere between 500 and 100,000 volts. Vacuum electrical feedthroughs enable you to increase your electrical voltage by approximately 10X—from 3kV/mm to a whopping 30kV/mm!
Recently, however, we have fielded a number of calls from customers whose electrical systems have shorted because their power is connected while they’re producing a high or ultra-high vacuum environment. When you’re using a roughing pump to evacuate your vacuum system, the pressure of your vacuum vessel will drop, which can produce “glow discharge.” In essence, if you flip on the power to your system before you have created a high or ultra-high vacuum, gases that breakdown electricity at particular voltages are present, which creates a tenuous situation, running the risk of shortages and power failure.
In addition, the breakdown voltage of gases such as argon and neon are much lower than air, which makes glow discharge more prevalent if you’re attempting to make electrical connections within gas-filled chambers.
The best way to prevent electrical shorts from “glow discharge” for any vessel or unit is to make sure that during the pump down stage, when you’re rough pumping to evacuate your system, that the power to all systems is disconnected. It is necessary to supply power to the feedthrough when you reach the threshold of 1×10 -3 for safety reasons, but we at MPF advise you to keep the power disconnected until you’re in a high vacuum.
Click here for more information on glow discharge.
