Impulse Voltage Generator design and the potential impact on Vacuum Interrupter de-conditioning

Impulse Voltage Test Systems based on a Marx multiplier circuit are often used to simulate lightning impulses to test electrical components and systems. The Impulse Voltage Generator (IVG) or Marx generator is the heart of the system and comes in many shapes and sizes but the basic circuit has, since the invention by Erwin Otto Marx in 1924, not radically changed. When testing to relevant International Standards, the pulse shape of the IVG output voltage is clearly defined, but the allowed stress imposed on the Test-Object, when a breakdown would occurs, is not prescribed in any way. In modern IVG designs, we see that substantially larger impulse capacitors are used compared to units build some years ago. It is demonstrated that because of this design change, the charge through the Test-Object, after a breakdown, has become substantially higher. As the conditioning or de-conditioning of Vacuum Interrupters (VI´s) is strongly related to the breakdown charge, the question raises if the pass or fail probability during impulse voltage testing would be IVG dependent. At first, the basic IVG circuit is looked at. After that, the impact of component choices on the current and charge through the Test-Object at a breakdown is discussed. Also the need to add additional resistors in the load circuit, to prevent high current oscillations, is addressed. Finally, a number of IVG´s in service in various test labs around the world has been compared and it is shown that the stress imposed on the Test-Object when a breakdown would occur varies widely from lab-to-lab.