1. Field of the Patent Application
The present disclosure is generally directed to contact assemblies for use with an electric power switching apparatus. More specifically, the present disclosure is generally directed to a moving contact assembly and a stationary contact assembly for use with an electric power switching apparatus. Such moving and stationary contact assemblies allow the switching apparatus to achieve a high withstand and close-on current ratings. For example, such withstand and close-on current ratings may achieve withstand and close-on current ratings of more than 10,000 A. In one arrangement, the present disclosure relates generally to a contact assembly arrangement that may be used for electrical power transfer and, more particularly, may be used in an automatic transfer switch. However, aspects of the invention may be equally applicable in other scenarios as well.
2. Description of Related Art
An automatic transfer switch is designed to provide a continuous source of power for critical loads by automatically transferring from a normal power source to an emergency power source when the normal power source falls below a preset limit. Automatic transfer switches are in widespread use in airports, subways, schools, hospitals, military installations, industrial sites, and commercial buildings equipped with secondary power sources and where even brief power interruptions can be costly or perhaps even life threatening.
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. A transfer switch can control electrical connection of utility power lines and the diesel generator to facility load buses. In certain installations, the transfer switch automatically starts a standby generator and connects the standby generator to the load bus upon loss of utility power. In addition, the transfer switch can automatically reconnect the utility power to the load bus if utility power is reestablished.
Automatic transfer switches are typically multi-pole switches. Therefore, an automatic transfer switch used with a three phase, four wire system will typically include three poles for switching the three phase conductors of the load between the three phase conductors of the normal power source and the three phase conductors of the emergency power source. The fourth, neutral conductor of the load is often permanently connected to the neutral conductors of the normal and emergency sources.
Unlike circuit breakers, which are designed to promptly open contacts (see for example, U.S. Pat. No. 6,977,568 which is herein entirely incorporated by reference and to which the reader is directed for further information), transfer switches are designed to remain in a closed state during certain fault conditions. For example, certain known circuit breakers employ the electromagnetic forces to blow contacts open and limit the amount of fault current that a system downstream may see. Certain transfer switches utilize contacts similar to circuit breaker design and overcome the blow off contact forces by employing mechanical operators with toggles.
Therefore, when used in a distribution system with circuit breakers, the transfer switch must have sufficient short circuit fault capability and protection so as to withstand and/or close-on short circuit and stay closed long enough to allow circuit breakers to open under the appropriate circumstances.
Accordingly, it would be desirable to provide a cost-effective automatic transfer switch that is easy to assemble and install. There is also a general need for an automatic transfer switch that can provide a sufficient short circuit fault protection while also allowing the contact assembly configuration to stay closed long enough to allow a system circuit breaker to open under the appropriate circumstances. There is also a general need for an enhanced automatic transfer switch designed to withstand and/or close on very high short circuit fault currents by employing electromagnetic forces to keep contacts closed.
According to an exemplary embodiment, a movable contact assembly for use with a switching mechanism comprising, a center portion, a first conductor portion extending from said center portion, the first conductor portion comprising a first arm comprising two longitudinal extending finger conductors. A second conductor portion extends from the center portion, the second conductor portion comprising a second arm comprising two longitudinally extending finger conductors. The moveable contact assembly may be pivoted about the center portion from a first position to a second position wherein in the first position, the two longitudinally extending finger conductors of the first conductor portion resides in a conductive state with a blade connector of a first stationary contact assembly of the switching mechanism. In the second position, the two longitudinally extending finger conductors of the second conductor portion resides in a conductive state with a blade connector of a second stationary contact assembly of the switching mechanism.
A movable contact assembly for use with a switching device, the moveable contact assembly comprising a center portion, a first conductor portion extending from said center portion, said first conductor portion comprising a first arm comprising a first blade connector; and a second conductor portion extending from said center portion, said second conductor portion comprising a second arm comprising a second blade connector. Said moveable contact assembly may be pivoted about said center portion from a first position to a second position wherein in said first position, said first connector blade of said first conductor portion resides in a conductive state with two longitudinally extending finger conductors of a first stationary contact assembly; and in said second position, said second connector blade of said second conductor portion resides in a conductive state with two longitudinally extending finger conductors of a second stationary contact assembly.
Exemplary embodiments are described herein with reference to the drawings, in which:
In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented herein. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the figures, can be arranged, substituted, combined, separated, and designed in a wide variety of different configurations, all of which are explicitly contemplated herein.
The present disclosure will be described in connection with a three phase, four wire system in connection with which a four-pole automatic transfer switch is employed. However, as those of ordinary skill in the art will recognize, Applicants' present disclosure has applicability within other types of power control and power providing systems as well. Three poles of the transfer switch panel assembly 20 are used to control power to the three phase conductors of the load. The fourth pole of the transfer switch panel assembly 20 controls connection of the load neutral conductor.
Referring now to
Generally, the automatic transfer switch panel assembly 20 is in an operating configuration wherein power from a primary power source can pass through the automatic transfer switch. Accordingly, most “first” positions or normally closed positions discussed and described herein generally correspond to this operating configuration (see, e.g.,
Various aspects of the disclosed transfer switch contact arrangements are described in association with an automatic transfer switch having a single phase. However, as those of ordinary skill will recognize, the disclosed transfer switch contact arrangements may be 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.
Under a first operation where a plurality of moveable contact assemblies 60a-d reside in a first or bottom position and as illustrated in
By some external means (such as an automatic transfer mechanism or a manual operator), the contact shafts 88, 94 may be rotated to various positions thereby connecting and/or disconnecting the movable contact assemblies and the stationary contact assemblies. For example, as illustrated in
As can be seen from
As can also be seen from
Returning to
As can also be seen from
As can also be seen from
In one preferred configuration, the movable contact assemblies 60a-d can be simultaneously connected to the first plurality of stationary contact assemblies 40a-d, and simultaneously disconnected from second plurality of stationary contact assemblies 50a-d.
Other connection and disconnection configurations are also possible. As just one example, the movable contact assemblies 60a-d can be connected to the first plurality of stationary contact assemblies 40a-d prior to and/or after they are disconnected from second plurality of stationary contact assemblies 50a-d. As those of skill in the art will recognize, alternative connection and disconnection configurations may also be utilized.
In addition, as those of skill in the art will recognize, alternative movable and stationary contact assembly arrangements may also be utilized. As just one example, in one alternative arrangement, the movable contact assemblies 60a-d may comprise one or more blade connectors and the stationary contact assemblies 40a-d, 50a-d may comprise one or more longitudinally extending finger conductors. Alternatively, a transfer switch may be provided were certain of the movable contact assemblies 60a-d comprising the longitudinally extending finger conductors whereas certain stationary contact assemblies 40a-d, 50a-d may comprise longitudinally extending finger conductors. Other contact assembly arrangements may also be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented herein. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the figures, can be arranged, substituted, combined, separated, and designed in a wide variety of different configurations, all of which are explicitly contemplated herein.
The transfer switch panel assembly 20 further comprises a plurality of conductors 110a-d and the transfer switch is configured to comprise the same number conductors as moveable contact assemblies 60a-d. Basically, and as will be described in greater detail below, each of the plurality of movable contact assemblies 60a-d are pivotally bolted or secured to one of the plurality of conductors 110a-d. In this manner, the movable contact assemblies 60a-d remain in permanent conductive contact with these conductors 110a-d. As just one example, and as can be seen from
As illustrated in
As can be seen from
Similarly, and as illustrated in
As illustrated in
As such, when the connector blade 46a first meets the first and second finger conductors 72a, 74a, the possibility of contact bounce is reduced since the connector blade 46a will smoothly enter between the finger conductors as the widths of both are generally equivalent. In one preferred arrangement, this movement may be aided by providing an attenuated edge along an outermost blade connector portion. As the blade connector 46a moves in-between the finger conductors 72a, 74a, there will be reduced frictional drag on the moving finger conductors 72a, 74a despite the fact the spring arrangement 120 provides a certain amount of contact pressure between the blade connector and the first and second finger conductors.
For example,
The overall contact pressure created by the spring arrangement 120 is increased as a result of the force of attraction between two finger conductors 72a, 74a as the total current flows in the same direction but is generally divided between both of the parallel finger conductors of the first arm. For example, during a high current fault condition (such as on the order of 10,000 Amps), the total current flowing through the switch contact may be represented by ITotal 140. This total current is divided generally equally between a first current I1 142 flowing through the first finger conductor 72a and a second current flowing I2 144 through the second finger conductor 72b. As such, the first current I1 142 will generate a first magnetic field FMag #1 160 and the second current I2 144 will generate a second magnetic field FMag #2 162. Consequently, this enhanced automatic transfer switch can withstand and/or remain closed during very high short circuit fault currents by employing electromagnetic forces to maintain contact closure.
An additional advantage of this arrangement is that due to the relative size of the movable contact tips 112,116 and stationary contact tips 102, 106, the total contact surface between the finger conductors 72a, 74a which engage connector blade 46a is quite large, thereby considerably increasing the useful life of these contact components. For example, one approximate size of the movable contact tips may be on the order of approximately 0.5×0.5 inches.
For example, as illustrated in
For example, the contact pressure needs to be adequate to allow for a low friction sliding motion between contact tips 102, 106 and 112, 116. When the movable contact assemblies and stationary contact assemblies connect, the conductive fingers with attached contact tips are forced spread apart by the stationary contact blade connector with attached contact tips. Low sliding friction results in low insertion force, which in turn, results in faster closing and opening speeds of the complete switch apparatus. For example, when the movable and stationary contacts are opened, there must be sufficient air gap and over surface distance for good dielectric strength.
The contact tips preferably incorporate contact materials to further enhance their short circuit performance and extend endurance life. Preferably, these materials must comprise good anti-arc erosion properties and low sliding friction. In addition, the low electrical resistance and low mechanical friction contact interface between contact tips and is a function of the specific materials used for theses contact tips. As just one example, preferred contact materials of the contact tips could include: copper, copper-chromium-zirconium, silver, silver-nickel, silver-copper, silver-tungsten, silver-tungsten-carbide, silver-tin oxide, silver-cadmium oxide, silver-zinc oxide, and tungsten-copper.
For example, one preferred contact tip alloy comprises of 85% silver, 15% cadmium oxide for the stationary contact tips 102, 106, and a preferred contact tip alloy of 50% silver, 50%$ tungsten carbide for the movable contact tips 112, 116. Alternative contact tip alloy compositions may also be used. As just one example, both the stationary contact tips and the movable contact tips may comprise a similar alloy composition.
During a short circuit fault (i.e., an abnormally high current condition of, for example 10,000 Amps or more) the geometry and location of the movable and stationary contacts creates magnetic forces that cause the movable contacts to clamp onto the stationary contact. As discussed above, this magnetic clamping action prevents contact separation (blowing-off).
While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope being indicated by the following claims, along with the full scope of equivalents to which such claims are entitled. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting.
Number | Name | Date | Kind |
---|---|---|---|
2233336 | Bentley | Feb 1941 | A |
2931876 | Weinfurt | Apr 1960 | A |
3632935 | Stegmaier | Jan 1972 | A |
4063204 | McFarlin | Dec 1977 | A |
4090046 | Faust et al. | May 1978 | A |
4251700 | Zaffrann et al. | Feb 1981 | A |
4321436 | McGarrity | Mar 1982 | A |
4395606 | Zaffrann et al. | Jul 1983 | A |
4584621 | Yang | Apr 1986 | A |
4745244 | Spinner | May 1988 | A |
4875278 | McIntosh | Oct 1989 | A |
4944083 | McIntosh | Jul 1990 | A |
5945650 | Holland et al. | Aug 1999 | A |
6222139 | Pandit et al. | Apr 2001 | B1 |
6265685 | Faure et al. | Jul 2001 | B1 |
6765157 | Rademacher et al. | Jul 2004 | B2 |
8040664 | Makinson et al. | Oct 2011 | B2 |
20020057145 | Kern et al. | May 2002 | A1 |
Number | Date | Country | |
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20140218140 A1 | Aug 2014 | US |
Number | Date | Country | |
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61760756 | Feb 2013 | US |