Arc suppression

[6] Every time an electrical power device (for example: heaters, lamps, motors, transformers or similar power loads) turns on or off, its switch, relay or contactor transitions either from a CLOSED to an OPEN state ("BREAK") or from an OPEN to a CLOSED state ("MAKE"), under load, an electrical arc occurs between the two contact points (electrodes) of the switch.

The temperature of the resulting electric arc is very high (tens of thousands of degrees), causing the metal on the contact surfaces to melt, pool and migrate with the current.

The high temperature of the arc causes dissociation of the surrounding gas molecules creating ozone, carbon monoxide, and other compounds.

The arc energy slowly destroys the contact metal, causing some material to escape into the air as fine particulate matter.

These micro-welds are a desired and important power contact feature as they ensure vibration-resistant, low ohmic, and non-permanent electrode connections.

The initial BREAK T-Arc is created after the explosion of the super-heated molten-metal bridge that had been carrying current as the contact begins to open.

In industrial, military and consumer electronic design, the latter method generally applies to devices such as electromechanical power switches, relays and contactors.

The unsuppressed and suppressed arc energy is expressed in Watt seconds [Ws] or Joules [J].

There are two distinct forms of electronic contact arcing, each defined by its respective arc initiation mechanism (note that arc initiation is not the same as plasma ignition; i.e., arcs initiate before their plasmas ignite). The two types of contact arc initiation mechanisms are: 1. The Thermionic-Emission-Initiated-Arc (T-Arc) is born out of Current and initiates around V(T-Arc_init_min), and the T-Arc plasma is maintained at or above the minimum-arc-current of I(arc_plasma_min). 2. The Electron Field-Emission-Initiated-Arc (F-Arc) is born out of Voltage and initiates around V(F-Arc_init_min), and the F-Arc plasma is maintained at or above the minimum-arc-current of I(arc_plasma_min). Both T-Arcs and F-Arcs require the combination of a minimum arc-initiation-voltage and a minimum arc-plasma-supporting-current of 300mA to 1000mA. We refer to these current and voltage combinations as the respective T-Arc Domain and F-Arc Domain.
The Domains of Existence for Thermionic-Emission-Initiated Arcs ("T-Arcs") and Electron-Field-Emission-Initiated-Arcs ("F-Arcs")
Potential MAKE F-Arc plasma extinguishes with the initial MAKE contact impact, followed by a series of MAKE -bounce-T-Arcs.
The " BREAK Arc" consists of an initial BREAK T-Arc, and is then extended by from one to possibly thousands of BREAK F-Arcs until the contact comes to rest in the OPEN state.
Physical effects of contact arcing - from left to right: pristine unused contact; failed contact after < 100 k unsuppressed cycles (i.e., typical use); used contact in excellent shape after 100 k suppressed cycles; used contact still in excellent shape after 1 million suppressed cycles (a 10x improvement).
Screen captures from an oscilloscope measuring the arc energy: current shown by blue line (sinusoidal wave), 2V/div = 5A/div; voltage shown by red line ,10V/div.
(left) Unsuppressed AC power electrical arc
(right) An identical arc with suppression.
Contact Arc Suppression Factor (CASF) test set-up. The results obtained using this test set-up allow for determining the effectiveness of a contact arc suppression on either an electromechanical relay or a contactor.
An electronic power contact arc suppressor attached in parallel across the contact of a relay or contactor (Fig. 1 of issued patent U.S. 8,619,395 B2)