Contactors are the heart of motor starters and many other electrical installations and panels. Simply put, contactors make and break electrical currents. A contactor consists of a coil/core (set) and the actual contacts. The contacts are most often made from silver alloy, while the outer body of the contactor is heat resistant.
While there are at least four different contactor types, this blog will focus specifically on vacuum and air- break contactors. There are several features that should be considered when comparing a vacuum contactor to an air- break contactor. The differences in arcing time and temperature, contact welding risk and oxidation, electrical and mechanic life, and maintenance – these elements set the two contactors apart from one another.
The common applications for vacuum make and break in mining and pumping are mainly due to their voltage utilization level. Vacuum contactors are inherently better suited for switching voltages above 600 V. Chopping current technology plays a role in the performance of contactors by controlling the voltage to the motor. When contactors have a low chopping current, the surge of voltage to the motor is smaller. Air-break and vacuum devices each have their own place at these voltage levels, and the optimum choice in each situation is dependent on various factors such as arcing time and temperature, contact welding risk and oxidation, along with electrical and mechanical life.
Arcing Time and Temperature
The vacuum contactor’s contacts are built into a vacuum-sealed bottle. The air-break contactor has much longer arc time and higher arc temperature than the vacuum. This degrades the contacts, resulting in frequent replacement and maintenance.
Contact Welding Risk and Oxidation
Air- break contactors pose a higher risk of contact welding and oxidations because of the increased arc time and higher temperature. This raises the resistance at low currents, presenting a voltage drop that could affect your application. Some air- break contactors have plated contacts that can be worn through.
Electrical and Mechanical Life
Contacts being inside a vacuum bottle offer better electrical life. The vacuum contactor features a robust interrupter and lasts over one million mechanical cycles. The interrupter creates smaller gaps between the contacts, eliminating the chances of air striking the arc.
The vacuum contactor wins in each category when compared to an air- break contactor in rugged, heavy duty applications. Although it has a higher cost up front, the vacuum contactor offers long life, reliable operation, and low maintenance and even lower total cost of ownership. All things considered, the vacuum contactor is ideal for mining and pumping applications as well as others in harsh environments.