Patent Application
20180090291
The present invention relates to the field of contactors and specifically to contactor actuators.
A “contactor” is an electrically controlled switch used for switching an electrical power circuit, similar to a relay except with higher current ratings. An electromagnetic ‘actuator’ is typically that part of the contactor mechanism which electrically controls the switching, i.e. opening and closing the electrical contacts of the switch. When a contactor is used for handling high currents to power hungry loads, such as electric motors, faults in the power supply may create abnormally high or so-called “short circuit” currents leading to a situation where the switch contacts are fused, i.e. welded, together as discussed below.
The person of ordinary skill in the art will understand that known contactors are typically equipped with some sort of spring to take up any decrease in electrical contact thickness as the contacts wear. The force needed to compress these springs must be generated by the actuator. When the contactor is closed in normal operation, the contacts have electrical continuity, and the contact spring is not fully compressed.
The movable contacts, also known as “bridging contacts,” and the contact springs are usually carried by a movable contact carrier, also sometimes known as a “rake,” of the electromagnetic actuator. The movable contact carrier is moved by the electromagnet's armature. Under normal operating conditions, the armature of the actuator thus controls the contact position, i.e., open or closed.
However, short circuit current through the contact pair is often two to three orders of magnitude greater than the rated current carrying capacity of the contactor. These short circuit currents produce significant magnetic repulsion forces between the contacts, which can cause the contacts to “blow open,” compressing the spring to its solid height, and initiating a plasma arcing between the contacts. When the short circuit current ends, e.g. a protective circuit breaker trips, the magnetic repulsion stops, and the contact spring of a known contactor actuator pushes the contact pair back together. The blown open contacts, however, will have been subjected to the intense heat of the arc, and their surface metal may be in a liquid, molten, state when they come back into contact. Then, as the contacts cool below the melting point of the contact metal they can weld together such that the actuator can no longer open them, and control of the load is lost.
Thus there is a need for improved contactor operation to prevent contact welding.
In the invention the moveable contacts and the armature of the contactor actuator are mechanically decoupled from one another by using a bistable connection such as a set of permanent magnets on the movable contact carrier and on a coupling shaft of the armature. Thus in normal operation the movable contacts will follow the armature and have common movement therewith to operate normally in a first position in relation to one another. But, in extraordinary cases, the movable contacts and armature will assume a second position in relation to one another preventing a welding together of molten contacts by allowing the movable contacts to blow open, and stay open, when a short circuit occurs. The polarity of the permanent magnets enables two stable positions the contacts can adopt. If enough force, e.g. from a short circuit current, is placed on the contacts to push them apart, they will move from one position (closed) to the other position (open) independent of the armature position and remain open until being reset to avoid coming together in a molten state to weld together.
In certain aspects the present invention will include an electromagnetically controlled actuator for an electrical contactor comprising: a) a set of fixed contacts for electrical coupling to a load; b) a movable contact carrier with contacts on a top side for meeting the fixed contacts and a body forming a tubular cavity on a bottom side, the cavity having a wall; c) an actuator with a coil and i) a movable armature actuated by the coil, and ii) a coupling shaft fixedly attached to the armature and extending upwardly therefrom toward the movable contact carrier, and d) a bistable coupling mechanism for holding the coupling shaft in one of two positions in relation to the cavity wall on the bottom side of the movable contact carrier.
In certain aspects the electromagnetically controlled actuator may be arranged wherein the two positions include a first position which allows the movable contacts to touch the fixed contacts and a second position which does not allow the movable contacts to touch the fixed contacts.
In other aspects the electromagnetically controlled actuator may be arranged wherein the two positions include the first position being a normal operation position of the movable contact carrier and the second position being a blown apart position of the movable contact carrier.
In other aspects the electromagnetically controlled actuator may be arranged wherein the bistable coupling mechanism is magnetic with: the cavity wall of the movable contact carrier having a magnet therein with a top side of south polarity and a bottom side of north polarity, and the coupling shaft of the armature having a magnet thereon with a top side of north polarity and a bottom side of south polarity. In related aspects the electromagnetically controlled actuator may be arranged wherein the coupling shaft, the armature, and the coil are surrounded by a case. In further related aspects the electromagnetically controlled actuator may be arranged to have the cavity wall of the movable contact carrier fitting over an extended portion of the actuator case containing the actuator coupling shaft.
In other aspects the electromagnetically controlled actuator may be arranged wherein the bistable coupling mechanism is an over-center mechanism with springs and linkages having one end attached to the coupling shaft and the other end connected to the cavity wall of the movable contact carrier.
In other aspects the electromagnetically controlled actuator may be arranged to have a load connected to the fixed contacts. In related aspects the electromagnetically controlled actuator may be arranged wherein the load is a motor.
The foregoing and other advantages of the disclosed embodiments will become apparent upon reading the following detailed description and upon reference to the drawings, wherein:
As an initial matter, it will be appreciated that the development of an actual commercial application incorporating aspects of the disclosed embodiments will require many implementation specific decisions to achieve the developer's ultimate goal for the commercial embodiment. Such implementation specific decisions may include, and likely are not limited to, compliance with system related, business related, government related and other constraints, which may vary by specific implementation, location and from time to time. While a developer's efforts might be complex and time consuming in an absolute sense, such efforts would nevertheless be a routine undertaking for those of skill in this art having the benefit of this disclosure.
It should also be understood that the embodiments disclosed and taught herein are susceptible to numerous and various modifications and alternative forms. Thus, the use of a singular term, such as, but not limited to, “a” and the like, is not intended as limiting of the number of items. Similarly, any relational terms, such as, but not limited to, “top,” “bottom,” “left,” “right,” “upper,” “lower,” “down,” “up,” “side,” and the like, used in the written description are for clarity in specific reference to the drawings and are not intended to limit the scope of the invention.
The extended section of the case 35 is then closely surrounded by a tubular cavity, represented by a cylinder 43, formed with its wall 44 in the bottom of the movable contact carrier 29. Surrounding the movable contact carrier cylinder 43 within the body of the movable contact carrier 29 is a second magnet, the annular movable contact carrier magnet 45. The annular movable contact carrier magnet 45 has a top side with South polarity and a bottom side with North polarity, i.e. opposite that of the shaft magnet 39. The movable contact carrier 29 and the actuator case 35 are thus slidably coupled and connected during normal operation only by the magnetic attraction of shaft magnet 39 and movable contact carrier magnet 45 when the two magnets 39, 45 opposite faces are aligned.
In this normal case the movable contact carrier 29 will follow at a first position in relation to, and in common with, the movement of the actuator's coupling shaft 39 to close or open the contacts as the actuator moves up and down, respectively, upon activation and deactivation of the coil 33. If this magnetic bond is broken, say by the contacts blowing open under the force of a short circuit current, the movable contacts 23 will carry the movable contact carrier's cylinder 43 upward to a position where the two magnets 39, 45 similar poles are aligned and there the repulsive magnetic forces will hold the contacts 23, 25 apart in a second position relational to one another (i.e. movable contacts up) even though the armature 31 remains in the down position.
In
In
In
After the short circuit is interrupted by the upstream protective device (e.g. circuit breaker or fuse), the contactor would need to be reset to the normal OFFposition (
As seen in
While particular aspects, implementations, and applications of the present disclosure have been illustrated and described, it is to be understood that the present disclosure is not limited to the precise construction and compositions disclosed herein and that various modifications, changes, and variations may be apparent from the foregoing descriptions without departing from the invention as defined in the appended claims.
