T&D World Magazine
Field Test System Quantifies Vacuum Interrupter Remaining Life

Field Test System Quantifies Vacuum Interrupter Remaining Life

Vacuum Interrupters, Inc.'s new magnetron atmospheric condition (MAC) MAC-TS1 shop testing and MAC-TS2 field-service systems are for quantifying the remaining life of vacuum interrupters used in medium-voltage circuit protection devices.

Vacuum Interrupters’ MAC Test Set is based on leak rate tests conducted by the OEMs during manufacture of the vacuum interrupter bottle.

“MAC testing is based on the Penning discharge principle, which states that when a high voltage is applied to open contacts in a gas and the contact structure is surrounded with a magnetic field, the amount of current (ion) flow between the plates is a function of the gas pressure, the applied voltage, and the magnetic field strength,” explains Finley Ledbetter, president of Vacuum Interrupters, Inc. and co-developer of the MAC Testing System. “By using this test method we are able to determine the pressure in the interrupter and therefore predict remaining life expectancy.”

MAC tests require a magnetron and magnetic coils. Until recently, portable magnetrons either didn’t exist or were not robust enough for field use due to careful calibration requirements, while the generic magnetic coils were not available for a wide range of vacuum interrupter sizes. Vacuum Interrupters, Inc. has overcome these design challenges while developing condition-based maintenance (CBM) algorithms based on a database of performance data from more than 3,000 vacuum interrupter models. The result is two systems for shop and field testing that provide easily understandable predictive estimates of the remaining life in your vacuum interrupters.

Before the MAC-TS1 shop testing and MAC-TS2 field-capable vacuum interrupter test systems, technicians could only determine if a vacuum interrupter passed or failed using a high-voltage AC/DC test set (HiPot). Now, for the first time, electrical field service testing companies and maintenance technicians working with medium-voltage electrical distribution equipment can know how much effective life remains in a vacuum interrupter bottle whether they are testing in the shop or the field.

While vacuum interrupters are extremely rugged, designed to last up to 20 or 30 years, tens of thousands of these units are in operation today and nearing the end of their expected lifetimes. This means that large parts of the U.S. electrical grid are at risk. Vacuum interrupter failures can be catastrophic events that usually lead to the destruction of circuit protection devices and/or connected switchgear. MAC Testing offers the only sure way to know whether your medium-voltage equipment is fully protected from a vacuum interrupter failure.

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