Weld-free contact system for electromagnetic contactors

A variable fault current tolerable contactor comprising:

• a contactor housing having at least one stationary contact therein;
• a movable contact carrier movable within the contactor housing and having an upper enclosure;
• at least one movable contact mounted within the movable contact carrier and in operable association with the stationary contact, the at least one movable contact being switchable between an open position and a closed position, and while in the closed position, allowing electrical current to flow through the stationary and movable contacts;
• an armature attached to the movable contact carrier;
• a movable contact biasing mechanism located between the upper enclosure of the movable contact carrier and the movable contact to bias the movable contact toward the stationary contact;
• an armature biasing mechanism located between the armature and a base portion of the contactor housing to bias the armature towards the stationary contact;
• an electromagnetic coil mounted in the contactor housing, the electromagnetic coil having an activation power threshold to attract the armature into the coil thereby engaging the movable contact wit the stationary contact, and a reduced holding power threshold to maintain engagement of the contacts;
• an arrangement in which an occurrence of a low fault current is compensated for by a contact material weld resistance;
• an arrangement in which an occurrence of an intermediate fault current causes the movable contacts to separate from the stationary contacts and remain open until the movable and stationary contacts have cooled sufficiently so as to avoid contact welding;
• and
• an arrangement in which an occurrence of a high fault current causes the armature to disengage from the electromagnetic coil until application of an energy pulse achieving the activation power threshold.

A method of preventing contact weld under fault conditions in a contactor comprising the steps of:

• providing a pair of contacts comprised of one of a silver oxide material, a silver tin oxide material, and a silver cadmium oxide material wherein at least one contact is movable between a closed position and an open position with respect to a stationary contact;
• energizing a coil with an energy pulse reaching an activation power threshold source to create an electrical current path through the pair of contacts when the contacts are in a closed position;
• providing latching of the movable contact from the stationary contact during an intermediate fault current until the contacts have cooled sufficiently so as to avoid a welding of the movable contact to the stationary contact;
• and
• permitting disengagement of an armature from the coil under a high fault current to prohibit the movable contact from engaging the stationary contact until application of an energy pulse achieving the activation power threshold.