Transfer switch with bypass topology

An automatic transfer switch (ATS) for supplying power to a load is provided. The ATS includes a main transfer switch portion configured to connect one of a first or second power source to the load. The ATS also includes a bypass transfer switch portion configured to form a bypass connection from either the first or second power source to the load. The bypass transfer switch portion includes (i) a first bypass switch configured to connect the first power source to the load upon closing of the first bypass switch and (ii) a second bypass switch configured to connect the second power source to the load upon closing of the second bypass switch. Further, the ATS includes a primary load connection connecting the main transfer switch portion to the load, where the primary load connection is formed at least in part by the first and second bypass switches.

BACKGROUND

An automatic transfer switch (ATS) 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 one or more predetermined events occur (e.g., the normal power source falls below a preset limit). Automatic transfer switches are in widespread use in, for example, 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. For instance, 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.

In an example, a transfer switch may include a main transfer switch and a bypass feature. The bypass feature typically includes a secondary electro-mechanical switching device (bypass switch) that can route power to the load in a fashion which circumvents the main transfer switch. This bypass feature allows, for example, (i) switch redundancy if a problem arises with the main transfer switch, (ii) exercising the main transfer switch without a load connection, and (iii) isolation for maintenance of the main transfer switch while ensuring the continuity of power to the load or loads.

SUMMARY

In one example aspect, an ATS configured for supplying power to an electrical load is provided. The ATS includes a main transfer switch portion configured to connect either a first power source or a second power source to the load. The main transfer switch portion includes (i) a first main switch configured to connect the first power source to the load upon closing of the first main switch and (ii) a second main switch configured to connect the second power source to the load upon closing of the second main switch. The ATS further includes a bypass transfer switch portion configured to form a bypass connection from either the first power source or the second power source to the load. The bypass transfer switch portion includes (i) a first bypass switch configured to connect the first power source to the load upon closing of the first bypass switch and (ii) a second bypass switch configured to connect the second power source to the load upon closing of the second bypass switch. The ATS still further includes a primary load connection connecting the main transfer switch portion to the load, wherein the primary load connection is formed at least in part by the first bypass switch or the second bypass switch, and wherein closing of either the first bypass switch or the second bypass switch severs the primary load connection between the main transfer switch portion and the load.

In another example, the ATS includes a main transfer switch portion configured to connect either a first power source or a second power source to the load. The main transfer switch portion includes (i) a first main switch configured to connect the first power source to the load upon closing of the first main switch and (ii) a second main switch configured to connect the second power source to the load upon closing of the second main switch. The ATS further includes a bypass transfer switch portion configured to form a bypass connection from either the first power source or the second power source to the load. The bypass transfer switch portion includes (i) a first bypass switch configured to connect the first power source to the load upon closing of the first bypass switch and (ii) a second bypass switch configured to connect the second power source to the load upon closing of the second bypass switch. The ATS still further includes a primary load connection connecting the main transfer switch portion to the load, wherein the primary load connection is formed at least in part by the first bypass switch or the second bypass switch, and wherein closing of either the first bypass switch or the second bypass switch severs the primary load connection between the main transfer switch portion and the load. Still further, the ATS is configured such that the main transfer switch portion no longer provides power to the load when the bypass switch portion is activated to form a bypass connection from either the first power source or the second power source to the load.

In another example, a method is provided for electrically isolating the main transfer switch portion from the bypass transfer switch portion without physically separating the main transfer switch portion from the bypass transfer switch portion. The method may, for example, be performed by an ATS in accordance with the present disclosure. The ATS may include (i) a main transfer switch portion configured to connect one of a first power source or a second power source to the load (ii) a bypass transfer switch portion configured to form a bypass connection from either the first power source or the second power source to the load, and (iii) a primary load connection connecting the main transfer switch portion to the load via the bypass transfer switch portion. In an example embodiment, the method involves the bypass switch activating to form the bypass connection from either the first power source or the second power source to the load, wherein activating to form the bypass connection severs the primary load connection connecting the main transfer switch portion to the load via the bypass transfer switch portion, and wherein severing the primary load connection isolates the main transfer switch portion from the load.

DETAILED DESCRIPTION

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. As just one example, Applicants' figures comprise one line diagrams, but those of ordinary skill in the art will recognize that such figures are merely illustrative and that these figures may comprise other configurations such as representing poles to switch one, two, or three phases of power (lines) and also a neutral switching pole.

A typical arrangement for an ATS having a bypass portion is depicted inFIG. 1. In particular,FIG. 1depicts an ATS100having a main transfer switch portion102and a bypass transfer switch portion104. The main transfer switch portion102is configured to connect either a first power source106or a second power source108to a load110. The main transfer switch portion102includes a first main switch112configured to connect the first power source106to the load110upon closing of the first main switch112. The main transfer switch portion102further includes a second main switch114configured to connect the second power source108to the load110upon closing of the second main switch114. The main portion102illustrated inFIG. 1, as well in any main portion described herein, may comprise two switching mechanisms as herein described, but could also be one switching mechanism that is arranged to be closed on either S1or S2, such as a true double throw configuration with no intentional open position. Alternatively, such switching mechanism could also comprise a true double throw switch with an open position.

The bypass transfer switch portion104is configured to form a bypass connection from either the first power source106or the second power source108to the load110. The bypass transfer switch portion104includes a first bypass switch116configured to connect the first power source106to the load110upon closing of the first bypass switch116. The bypass transfer switch portion104further includes a second bypass switch118configured to connect the second power source108to the load110upon closing of the second bypass switch118.

ATS100also includes three isolation contacts120,122, and124, such as self aligning jaws that allow for consistent alignment with bus stabs. As such, ATS100depicted inFIG. 1can be described as two transfer switches arranged in a series-parallel arrangement, with three isolation contact points between the two transfer switches. Isolation contact120may serve to isolate the main transfer switch portion102from the first power source106. Further, isolation contact122may serve to isolate the main transfer switch portion102from load110. Still further, isolation contact124may serve to isolate the main transfer switch portion102from second power source108.

As typically constructed, the isolation contacts120,122, and124(such as the self-aligning jaws described above) are not capable of interrupting current, as they have no arc extinction capability. Therefore, a proper sequence to isolate the transfer switch100is to operate the bypass portion104so that it is in parallel with the main portion102. For example, both the main and bypass portion switches112,116, respectively, can be closed on the first power source S1106. Then the main portion102can be drawn out of the switch100and the isolation contacts120,122, and124can then be separated. This sequence of operation results in insignificant voltage appearing across the isolation contacts (because they are bypassed) and prevents any arcing during the isolation operation. If the main portion102is open from both sources S1and S2, the isolation contacts120,122,124can be separated (i.e., the switch may be drawn out) because no current is flowing through any of the isolation contacts.

This typical ATS arrangement shown inFIG. 1suffers from certain perceived limitations and disadvantages. Due to the nature of their mechanical design, coordination of the main transfer switch position is needed when activating and deactivating the bypass and isolation features. This coordination is typically facilitated by mechanical and/or electrical interlock mechanisms that are provided to prevent unintentionally inducing a short-circuit between the power sources across the two switching mechanisms. For example, this arrangement depicted inFIG. 1requires interlocking between main transfer switch portion102and bypass transfer switch portion104(e.g., mechanical and/or electrical interlocks) to ensure that a short-circuit between the two power sources S1and S2cannot be created via a combination of the positions of main transfer switch portion102and positions of bypass transfer switch portion104. Such interlocking between the main transfer switch portion102and the bypass transfer switch portion104can add to the complexity of the ATS as well as the cost of the ATS (e.g., the cost of manufacturing the ATS and/or servicing the ATS).

Likewise, similar coordination and protection is needed when electrically isolating and reconnecting the main transfer switch portion102to and from the bypass transfer switch portion104. These coordination and protection functions are inherently provided by design but, depending upon the implementation, can add complexity to the product and its usage. The arrangement depicted inFIG. 1requires a distinct step to mechanically or electrically isolate the main transfer switch portion102from the bypass transfer switch portion104. This distinct isolation step is typically achieved by physically separating (i.e., manually or automatically) the two portions at the isolation contact points. This isolation step may be both difficult and time consuming, thereby adding to the difficulty of servicing the ATS and/or the time required to service the ATS.

Since bypass operations may be conducted during a time of operator duress (e.g., such as during a power outage), it is desirable to make the operating method as easy and as intuitive as possible. Thus, a means is needed to simplify the operating process, reduce complexity, but still maximize safety to remove the potential for unintended consequences such as short-circuits.

These example problems associated with existing ATSs such as ATS100can be addressed by the new topology disclosed in the present application. An example ATS in accordance with the present disclosure may include a main transfer switch portion configured to connect either a first power source or a second power source to the load. The main transfer switch portion may include (i) a first main switch configured to connect the first power source to the load upon closing of the first main switch and (ii) a second main switch configured to connect the second power source to the load upon closing of the second main switch. The ATS may also include a bypass transfer switch portion configured to form a bypass connection from either the first power source or the second power source to the load. This bypass transfer switch portion may include (i) a first bypass switch configured to connect the first power source to the load upon closing of the first bypass switch and (ii) a second bypass switch configured to connect the second power source to the load upon closing of the second bypass switch. The ATS may also include a primary load connection connecting the main transfer switch portion to the load, wherein the primary load connection is formed at least in part by the first bypass switch and the second bypass switch, and wherein closing of either the first bypass switch or the second bypass switch severs the primary load connection between the main transfer switch portion and the load. The ATS may be further configured such that the main transfer switch portion is electrically isolated from the load, first power source, and second power source when the bypass switch portion is activated to form a bypass connection from one of the first power source or the second power source to the load.

Beneficially, this disclosed topology has the mechanisms arranged in a way that removes the need for an interlock mechanism between the main transfer switch portion and the bypass transfer switch portion. Further, the disclosed topology also beneficially removes the need for a distinct load isolation step, typically referred to in the art as a rack-out step. Still further, the disclosed topology beneficially removes the potential for introduction of a short-circuit when activating or deactivating the bypass mechanism.

2. EXAMPLE ATS SYSTEMS AND METHODS

FIG. 2is an illustration of an example ATS in accordance with an embodiment of the present disclosure. In particular,FIG. 2depicts an ATS200having a main transfer switch portion202and a bypass transfer switch portion204. The main transfer switch portion202is configured to connect either a first power source206or a second power source208to a load210. The first power source may, for example, be a normal source of electrical power for the load210, while the second power source208may be an emergency source of power for the load210. The ATS200may be operable to transfer electrical load210from the normal source of electrical power to the emergency source of electrical power upon the occurrence of one or more predetermined events.

The main transfer switch portion202includes a first main switch212configured to connect the first power source206to the load210upon closing of the first main switch212. The main transfer switch portion202further includes a second main switch214configured to connect the second power source208to the load210upon closing of the second main switch214. First main switch212and second main switch214may each include a stationary contact and a movable contact. For example, first main switch212includes movable contact212aand stationary contact212b. When first main switch212is closed, movable contact212aand stationary contact212bare connected to one another. These stationary contacts may be connected to a conductor (e.g., a rigid conductor) that communicates with one of power source206or power source208. For example, as shown inFIG. 2, stationary contact212bis connected to power source206via conductors213and215.

It may be necessary in some circumstances to perform maintenance work on the main transfer switch portion202or even to replace it in part or in its entirety. Therefore, bypass transfer switch portion204may be employed to provide continuity of power to the load210while the main transfer switch portion202is out of service. As such, the bypass transfer switch portion204is configured to form a bypass connection from one of the first power source206or the second power source208to the load210. The bypass connection circumvents the main transfer switch portion202upon activation of the bypass transfer switch portion204, in order to supply power to the load210. The bypass transfer switch portion204includes a first bypass switch216configured to connect the first power source206to the load210upon closing of the first bypass switch216. The bypass transfer switch portion204further includes a second bypass switch218configured to connect the second power source208to the load210upon closing of the second bypass switch218.

ATS200also includes a primary load connection220connecting the main transfer switch portion202to the load210. As shown inFIG. 2, the primary load connection220is formed at least in part by the first bypass switch216and the second bypass switch218(in particular, when the first bypass switch216and the second bypass switch218are both in the open position). Closing of either the first bypass switch216or the second bypass218switch severs the primary load connection220between the main transfer switch portion202and the load210. As mentioned above, the primary load connection220is formed at least in part by the first bypass switch216and the second bypass switch218. In an example, the switches216,218form the entire primary load connection220between isolation contact point222and load210. However, in another example, the switches216,218form part of the primary load connection220between isolation contact point222and load210. For example, the switches216and218may be separated by a conductor line (e.g., a rigid connector) connecting switch216to switch218. That is, switches216and218may not be adjacent to one another as shown inFIG. 2, but may instead be separated by a conductor.

The primary load connection220further includes a first load-isolation contact222and a second load-isolation contact224. The first bypass switch216connects to the first load-isolation contact222when216a is closed to contact222, as shown inFIG. 2. Further, the second bypass switch218connects to the second load-isolation contact224when switch218is closed to the load210, as shown inFIG. 2. It should be understood that the schematic drawing of ATS200shows one example configuration of how bypass switch216and bypass switch218(including load-isolation contact222and load isolation contact224) may together form primary load connection220. However, it should be understood that this is merely one example orientation, and the primary load connection in accordance with the present disclosure may be formed in other ways.

First bypass switch216and second bypass switch218may include a stationary contact, movable contact, and the load-isolation contact. For example, first bypass switch216includes movable contact216a, stationary contact216b, and load-isolation contact222. When first bypass switch216is closed, movable contact216aand stationary contact216bare connected to one another. These stationary contacts may be connected to a conductor (e.g., a rigid conductor) that communicates with one of power source206or power source208. For example, as shown inFIG. 2, stationary contact216bis connected to power source206via conductor215.

The main transfer switch portion202may have three alternative conditions. In particular, a first condition is first main switch212closed and second main switch214open. For instance,FIG. 3depicts ATS200having first main switch212closed and second main switch214open. In this first condition, the first main switch212is connected to the first power source206. A second condition is first main switch212open and second main switch214closed.FIG. 4depicts ATS200having first main switch212open and second main switch214closed. In this second condition, the second main switch214is connected to the second power source208. A third condition is a neutral condition with first main switch212open and second main switch214open (e.g., as shown inFIGS. 5 and 6). In this neutral position, power may be supplied to the load via the bypass transfer switch portion204. It is a major advantage of Applicants' disclosed bypass topology that the load may be supplied via the bypass portion203while the main portion is in any position (i.e., closed to S1, closed to S2, or open). This may be appropriate in other parts of this disclosure as well.

The bypass transfer switch portion204may have three alternative conditions. In particular, a first condition is where first bypass switch216is closed to switch216band second bypass switch218is closed to the load210.FIG. 5depicts ATS200having first bypass switch216closed to switch216band second bypass switch218closed to the load210. In this first condition, the first bypass switch216is connected to first power source206. A second condition is first bypass switch216closed to switch222and second bypass switch218closed to the load210.FIG. 6depicts ATS200having first bypass switch216closed to switch222and second bypass switch218closed to load210. In this second condition, the second bypass switch218is connected to second power source208. A third condition is a neutral condition with first bypass switch216closed to switch222and second bypass switch218closed to the load210(e.g., as shown inFIG. 3-4). In this neutral position, power may be supplied to the load via the main transfer switch portion202. As seen inFIGS. 2-4, bypass switches216,218act to form the primary load connection220.

In an example embodiment, main transfer switch portion202may include an interlock mechanism between the first main switch and the second main switch. For example, as shown inFIG. 2, main transfer switch portion202may include interlock mechanism226. This interlock mechanism226may prevent the first main switch212and the second main switch214from closing at the same time. The interlock can comprise a link connecting the two switches, or the two switches212and214may actually be comprised of one double throw switch that either has or does not have an open position. This interlock mechanism may be any suitable interlock mechanism now known in the art or later developed. For instance, interlock mechanism226may be a mechanical interlock and/or an electrical interlock. Another major advantage of Applicants' disclosed bypass topology is that the interlock226is simply not required under any sequence of operation. The need for such an interlock is simply eliminated.

In another example embodiment, bypass transfer switch portion204may include an interlock mechanism between the first bypass switch and the second bypass switch. For example, bypass transfer switch portion204may include interlock mechanism228. The interlock mechanism228may prevent the first bypass switch216and the second bypass switch218from closing at the same time. This interlock mechanism may be any suitable interlock mechanism now known in the art or later developed. For instance, interlock mechanism228may be a mechanical interlock and/or an electrical interlock.

This proposed ATS200can be described as two transfer switches arranged in a dual series arrangement, with two load isolation contact points between the two transfer switches. This disclosed transfer-switch topology does not require an interlock mechanism between the main transfer switch portion202and the bypass transfer switch portion204. This is due to the fact that activation of either bypass switch216or218(i.e., closing of either bypass switch216or218) will sever the load connection220of the main transfer switch portion202. For instance, as can clearly be seen inFIG. 5, activation of bypass switch216to the closed position severs the primary load connection220. Similarly, as can clearly be seen inFIG. 6, activation of bypass switch218to the closed position severs the primary load connection220.

Therefore, as can be seen inFIGS. 5 and 6, the main switch portion202resides in a neutral position and is isolated from the load210. Consequently, this topology does not require a distinct isolation step that may be required with certain conventional ATSs. This disclosed topology for ATS200cannot produce a short-circuit via any combination of the main switch positions and the bypass switch positions. For instance, even if main switch212and bypass switch218are closed at the same time, the load210will only be connected to second power source208. Similarly, even if main switch214and bypass switch216are closed at the same time, the load210will only be connected to first power source206. Thus, once the bypass switch is activated, the main transfer switch portion can be exercised without switching the load(s) between the two power sources.

As described above, the topology depicted inFIG. 2beneficially isolates the main transfer switch portion202from the load210upon activation of the bypass switch; however, the topology shown inFIG. 2does not provide complete electrical isolation from the power source connections206,208. Complete isolation from the power sources may be desired for various reasons such as, for example, maintenance purposes. Therefore, an ATS in accordance with the present disclosure may be configured such that the main transfer switch portion is electrically isolated from the load, first power source, and second power source when the bypass switch portion is activated to form a bypass connection from one of the first power source or the second power source to the load.

In particular, complete electrical isolation from the power source connections206,208may be achieved in ATS200with the addition of two source-isolation contacts. Example placement of such additional source-isolation contacts is shown inFIG. 7. As shown, ATS200may include a first source-isolation contact230between the main transfer switch portion202and the first power source206. Further, ATS200may also include a second isolation-contact232between the main transfer switch portion202and the second power source208.

These source-isolation contacts230,232may be any suitable source-isolation contact. For example, these source-isolation contacts230,232may include self aligning jaws that interconnect with bus stabs. In an example embodiment, the first source-isolation contact230and the second source-isolation contact232are interlocked such that the first source-isolation contact230and the second source-isolation contact232are configured to open and close at the same time.

ATS200shown inFIG. 7results in a fully functional replacement to the original topology of ATS100shown inFIG. 1. This topology of ATS200provides example advantages over the topology depicted inFIG. 1. For instance, the ATS200provides reduced complexity of design and increased simplicity of operation. This may result in lower manufacturing costs, as well as faster and simpler maintenance of the ATS.

As discussed above, the disclosed ATS beneficially provides a method for electrically isolating the main transfer switch portion from the bypass transfer switch portion without physically separating the main transfer switch portion from the bypass transfer switch portion. In an example embodiment of the disclosed method, an ATS such as the ATS200may be provided. For example, the ATS may include (i) a main transfer switch portion configured to connect one of a first power source or a second power source to the load (ii) a bypass transfer switch portion configured to form a bypass connection from one of the first power source or the second power source to the load, and (iii) a primary load connection connecting the main transfer switch portion to the load via the bypass transfer switch portion. An example method may involve the bypass transfer switch portion activating to form the bypass connection from one of the first power source or the second power source to the load, wherein activating to form the bypass connection severs the primary load connection connecting the main transfer switch portion to the load via the bypass transfer switch portion, wherein severing the primary load connection isolates the main transfer switch portion from the load. In an example, the bypass switch may also electrically isolate the first power source and the second power source from the main transfer switch portion via respective source-isolation contacts.

The ATS described above with respect toFIGS. 2-7is depicted as a single phase ATS with which a single pole main switch and single pole bypass switch are employed. However, it should be understood that the disclosed ATS may be configured to have more poles, such as in a two-phase ATS, three phase ATS, and so forth. In addition, although the transfer switch described above is referred to as an automatic transfer switch, the disclosed method and system may apply to any suitable transfer switch, such as a manual transfer switch.

3. EXAMPLE BENEFITS OF THE DISCLOSED SYSTEMS AND METHODS

As described above, the proposed methods and systems beneficially provide an improved ATS and method for isolating a main transfer switch portion from a bypass transfer switch portion. The disclosed methods and systems provide a simpler topology for a bypass transfer switch that results in advantages over existing ATS topologies. The disclosed ATS provides a simple and safe means for activating and deactivating the bypass mechanism in the ATS. By using the disclosed ATS, users of the ATS (e.g., maintenance workers) who may be facing heightened stress and duress during a power outage or a transfer switch malfunction, may require fewer operational steps to conduct typical maintenance tasks associated with bypass transfer switches. For instance, the disclosed ATS removes the need for the user to physically separate the main transfer switch portion from the bypass transfer switch portion in order to electrically isolate the two switches. Further, the disclosed mechanical design removes the need for an interlock mechanism between the two switching devices. For these reasons and the reasons described throughout the disclosure, the disclosed methods and systems can help improve the operation and maintenance of a transfer switch having a bypass mechanism.