Patent Application
20110198203
1. Field
The disclosed concept pertains generally to separable contacts and, more particularly, to stationary contact assemblies. The disclosed concept also pertains to circuit interrupters including a stationary contact assembly. The disclosed concept also pertains to transfer switches including stationary contact assemblies.
2. Background Information
Transfer switches are well known in the art. See, for example, U.S. Pat. Nos. 7,569,949; 7,239,045; 6,849,967; 5,397,868; 5,210,685; 4,894,796; and 4,747,061. Transfer switches operate, for example, to transfer a power consuming load from a circuit with a normal power supply to a circuit with an auxiliary power supply. Applications for transfer switches include stand-by applications, among others, in which the auxiliary power supply stands-by if the normal power supply should fail. Facilities having a critical requirement for continuous electric power, such as hospitals, certain plant processes, computer installations, and the like, have a standby power source, often a diesel generator. A transfer switch can control electrical connection of utility power lines and the diesel generator to facility load buses. In many installations, the transfer switch automatically starts the standby generator and connects it to the load bus upon loss of utility power, and reconnects the utility power to the load bus if utility power is reestablished.
A transfer switch typically can comprise a pair of circuit interrupters combined with a drive input and a linkage system. The preferred types of circuit interrupters have been molded-case switches and molded-case circuit breakers because these types are commercially available in a wide array of sizes and are relatively economical compared to other options. The preferred type of drive input depends on the application for the transfer switch. Usually motors or solenoids are preferred, but at other times there is a clear preference for manually-operated mechanisms.
A typical automatic transfer switch (ATS) includes a housing, an operating mechanism, a first line bus, a second line bus, a load bus, a first line movable contact, a second line movable contact, a fixed contact assembly, and a control device. The operating mechanism, first line movable contact, second line movable contact, fixed contact assembly, and control device are disposed within the housing. Only one of the first and second movable contacts engages the fixed contact assembly at a time. That is, in the normal operating configuration, the first movable contact is in a second position, and is capable of providing electricity to a system load from a primary power source, and the second movable contact is in a first position. If the need arises, the first movable contact is moved into the first position while the second movable contact moves into the second position. The transfer can occur almost instantaneously. In this configuration, a secondary power source is capable of providing electricity to the system load. Operation (i.e., positioning of the first and second movable contacts) is performed by the operating mechanism.
It is known for circuit breakers to include a set of main contacts, an operating mechanism for opening the set of main contacts, a trip device to actuate the operating mechanism to trip the set of main contacts open in response to certain overcurrent conditions, a set of secondary contacts, and a remotely controllable actuator to control the open and closed states of the set of secondary contacts.
A known circuit breaker includes line and load terminals, and first and second circuit breaker mechanisms. Each of the first and second circuit breaker mechanisms includes a corresponding set of separable contacts in series between circuit breaker line and load terminals, a corresponding operating mechanism for moving the corresponding set of separable contacts between open and closed positions, and a corresponding trip mechanism cooperating with the corresponding operating mechanism for moving the corresponding set of separable contacts from the closed to the open position thereof.
U.S. Pat. No. 7,368,677 discloses a circuit breaker pole including a pair of main contacts that include a stationary main contact and a movable main contact. The movable main contact is carried by a moving conductor assembly. This moving conductor assembly includes a plurality of contact fingers, which are mounted in spaced axial relation on a pivot pin secured in a contact carrier. The contact carrier is rotated about pivots by an operating mechanism. A movable main contact is fixed to each of the contact fingers at a point spaced from the free end of the finger. The portion of the contact finger adjacent the free end forms a moving arcing contact or “arc toe”. A stationary arcing contact is provided on the confronting face of an integral arcing contact and runner mounted on a line side conductor. The stationary arcing contact and arc toe together form a pair of arcing contacts.
Automatic transfer switch power contactors preferably provide extensive endurance life. Typically, the stationary contacts thereof have superior anti-welding and temperature profiles.
There is room for improvement in stationary contact assemblies.
There is also room for improvement in a circuit interrupter employing a stationary contact assembly.
There is further room for improvement in a transfer switch employing stationary contact assemblies.
These needs and others are met by embodiments of the disclosed concept, which provide a first stationary contact disposed on a conductor, and a second stationary contact disposed on the same such conductor proximate the first stationary contact. The first stationary contact has a first contact surface disposed a first distance from the conductor, and the second stationary contact has a second contact surface disposed a second smaller distance from the conductor.
In accordance with one aspect of the disclosed concept, a stationary contact assembly comprises: a conductor; a first stationary contact disposed on the conductor; and a second stationary contact disposed on the same such conductor proximate the first stationary contact, wherein the first stationary contact has a first contact surface disposed a first distance from the conductor, wherein the second stationary contact has a second contact surface disposed a second distance from the conductor, and wherein the second distance is smaller than the first distance.
The first contact surface of the first stationary contact may be subject to wear such that the first distance is subject to being reduced to about the second distance; and after the wear, both of the first and second stationary contacts may be structured to be engaged by a movable contact.
The first stationary contact may be structured to resist arcing better than the second stationary contact; and the second stationary contact may be structured to be more durable than the first stationary contact.
The second stationary contact may be structured to cooperate with the first stationary contact in order to extend the endurance life of the stationary contact assembly.
The first stationary contact may include a first side and an opposite second side; the conductor may be a conductive mounting block; an arc runner may be disposed on the conductive mounting block adjacent the first side of the first stationary contact; and the second stationary contact may be disposed on the conductive mounting block adjacent the opposite second side of the first stationary contact.
As another aspect of the disclosed concept, a circuit interrupter comprises: a movable contact assembly comprising a movable contact; a stationary contact assembly comprising: a conductor, a first stationary contact disposed on the conductor, and a second stationary contact disposed on the same such conductor proximate the first stationary contact, wherein the first stationary contact has a first contact surface disposed a first distance from the conductor, wherein the second stationary contact has a second contact surface disposed a second distance from the conductor, and wherein the second distance is smaller than the first distance; and an operating mechanism structured to move the movable contact assembly and cause the movable contact to engage or disengage from at least the first contact surface of the first stationary contact.
As another aspect of the disclosed concept, a transfer switch comprises: two movable contact assemblies, each of the two movable contact assemblies comprising a movable contact; two stationary contact assemblies, each of the two stationary contact assemblies comprising: a conductor; a first stationary contact disposed on the conductor, and a second stationary contact disposed on the same such conductor proximate the first stationary contact, wherein the first stationary contact has a first contact surface disposed a first distance from the conductor, wherein the second stationary contact has a second contact surface disposed a second distance from the conductor, and wherein the second distance is smaller than the first distance; and an operating mechanism structured to move the two movable contact assemblies and cause the movable contact of a corresponding one of the two movable contact assemblies to either engage or disengage from at least the first contact surface of the first stationary contact of a corresponding one of the two stationary contact assemblies.
A full understanding of the disclosed concept can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which:
As employed herein, the term “number” means one or an integer greater than one (i.e., a plurality).
As employed herein, the term “coupled” means to directly or indirectly link, join or connect two or more elements.
As employed herein, the term “directly coupled” means that two elements are directly in contact with or directly connected to each other.
As employed herein, the term “stationary” means the same as the term “fixed”.
As employed herein and with reference to electrical components, the term “engage” means temporarily coupled and allowing for electrical communication.
As employed herein, the term “proximate” means adjacent with or without contact, immediately adjacent, adjoining, contiguous, directly abutting, or flush.
Generally, an automatic transfer switch is in an operating configuration wherein power from a primary power source can pass through the automatic transfer switch. Accordingly, most “first” positions disclosed herein correspond to this operating configuration. When the automatic transfer switch is in another operating configuration wherein power from a secondary power source can pass through the automatic transfer switch, most components are in “second” positions as disclosed herein. The exception to this convention is the position of first and second movable contacts. In order to have the description of the positions of such first and second movable contacts be consistent with each other, the first and second movable contacts are in their “first position” when the corresponding circuit is open (i.e., the movable contact does not engage a number of corresponding stationary contacts). Similarly, when either one of the first and second movable contacts is in its “second position,” the movable contact engages a number of corresponding stationary contacts. Thus, in a normal operating configuration, most components are in the “first position,” however, the first movable contact is in the “second position” (i.e., closed with power capable of flowing therethrough).
The disclosed concept is described in association with an automatic transfer switch having a single phase, although the disclosed concept is applicable to a wide range of transfer switches or circuit interrupters having any number of phases or poles, and to stationary contact assemblies for those and other electrical switching apparatus.
Referring to
As shown in
Referring again to
As shown in
The first movable contact 24 is coupled to, and in electrical communication with, the first line bus 18. The coupling between the first movable contact 24 and the first line bus 18 may be through a conductor, such as, but not limited to a copper wire or a flexible conductor (not shown), but is preferably a direct, but movable, coupling as shown in
Similarly, the second movable contact 26 is coupled to, and in electrical communication with, the second line bus 20. The second movable contact 26 is structured to move between a first position (as shown in
Only one of the first and second movable contacts 24,26 engages at least the corresponding first stationary contact 42 (as shown in
The configuration/position of the operating mechanism 16 is controlled by the actuator 32. The actuator 32, which typically includes a solenoid (not shown) or other suitable actuating device, is structured to receive a command signal from a user (not shown). Upon receiving a command signal, the actuator 32 is actuated and, via at least one actuator link 48 (two example actuator links 48 are shown in
Operation (i.e., positioning of the first and second movable contacts 24,26) is performed by the operating mechanism 16. That is, the operating mechanism 16 is structured to move the first movable contact 24 and the second movable contact 26 between their respective first and second positions. The operating mechanism 16 may be described, generally, as being in a first position, or configuration, when the first movable contact 24 is in the second (closed) position, while the second movable contact 26 is in the first (open) position, and, the operating mechanism 16 is in a second position, or configuration, when the first movable contact 24 is in the first (open) position, while the second movable contact 26 is in the second (closed) position. The operating mechanism 16 is preferably configured by a plurality of mechanical linkages (not numbered) to ensure that both the first and second movable contacts 24,26 are not in the second (closed) position at the same time. Both the first and second movable contacts 24,26 may, however, be in the first (open) position at the same time (i.e., the system load (not shown) would not be receiving power through the ATS 10). The operating mechanism 16 includes one or more springs (not shown) structured to maintain the engaged movable contact 24 or 26 in the second (closed) position.
A non-limiting example of the ATS 10, but excluding the disclosed stationary contact assemblies 28,29, is disclosed by U.S. patent application Ser. No. 12/466,780, filed May 15, 2009, entitled “Inertial Catch For An Automatic Transfer Switch Power Contactor”, which is incorporated by reference herein.
As shown in
As shown in
The first stationary contact 42 has a relatively high silver content and the second stationary contact 40 has a relatively lower silver content. In this manner, the first stationary contact 42 is relatively more conductive than the second stationary contact 40.
The first stationary contact 42 can be made, for example and without limitation, from 97% silver and 3% carbon.
The second stationary contact 40 can be made, for example and without limitation, from 50% silver and 50% tungsten.
The arc runner 48 and a spin rivet 50 can be made, for example and without limitation, from steel.
The example 50% silver-50% tungsten second stationary contact 40 is structured for durability. The example 97% silver-3% carbon first stationary contact 42 is structured for arcing and for operation at relatively lower temperatures. The example second stationary contact 40 is meant to help the example first stationary contact 42 at the end of the endurance life.
The example first stationary contact 42 is preferably flush with the arc runner 48. The arc runner 48, and the first and second stationary contacts 42,40 are preferably flush with side surface 52 of the mounting block 46.
The arc runner 48, and the first and second stationary contacts 42,40 are directly coupled (e.g., without limitation, brazed) to top surface 54 of the mounting block 46.
The spin rivet 50 ensures that there is no relative movement between the arc runner 48 and the mounting block 46.
One of the two movable contact assemblies 45 is structured to receive a first power source (not shown). The other one of the two movable contact assemblies 45 is structured to receive a second power source (not shown). The conductor 46 of one of the two stationary contact assemblies 28,29 is electrically connected by load bus 22 to the conductor 46 of the other one of the two stationary contact assemblies 28,29. The conductors 46 and the load bus 22 are structured to power a load (not shown).
The movable contact assembly 45 carries the corresponding movable contact 24 or 26. The movable contact assembly 45, over time, causes the corresponding movable contact 24 or 26 to wear the first contact surface 41 (as shown in phantom line drawing in
The second stationary contact 40 is structured to cooperate with the first stationary contact 42 in order to extend the endurance life of the transfer switch 10.
The second stationary contact 40 is disposed on the conductor 46 adjacent the first stationary contact 42.
The first contact surface 41 of the first stationary contact 42 can be subject to wear such that the first distance 47 is subject to being reduced to about the second distance 49. After such wear, both of the first and second stationary contacts 42,40 can be structured to be engaged by the corresponding movable contact 24,26.
The first stationary contact 42 can be structured to resist arcing better than the second stationary contact 40, which can be structured to be more durable than the first stationary contact 42.
The second stationary contact 40 can be structured to cooperate with the first stationary contact 42 in order to extend the endurance life of the stationary contact assembly 28,29, the transfer switch 10 and/or a circuit interrupter (e.g., without limitation, 62 of
Referring to
The stationary contact assemblies 28,29 of
The circuit interrupter 62 of
The movable contact assembly 45′ includes a movable arm 64′ carrying the movable contact 24′.
While specific embodiments of the disclosed concept have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the disclosed concept which is to be given the full breadth of the claims appended and any and all equivalents thereof.
