Key interlock system and method for safe operation of electric power distribution system

Key interlock systems and methods are described for safely carrying out a closed-transition procedure in an electric power distribution system in which two load busses that can be separately powered by the same power source or by two different power sources can be connected together via one or more bus tie breakers and in which a static transfer switch is used to selectively deliver power from one of the two different power sources to at least one of the load busses. Embodiments described herein prohibit access to a key that is required to close a bus tie breaker that connects the two load busses until at least a determination is made that a particular bypass breaker of the static transfer switch has been closed, thereby ensuring that both load busses are connected to the same power source.

BACKGROUND

In some electric power distribution systems, a main-tie-tie-main configuration is used. In accordance with a main-tie-tie-main configuration, a first load bus powered via a first main breaker and a second load bus powered via a second main breaker can be connected together by closing two bus tie breakers that are connected between the two load busses. The first load bus can be powered by the same power source as the second load bus or by a different power source. For example, the first load bus may be connected to a static transfer switch that can selectively deliver power to the first load bus from a first power source or a second power source while the second load bus may simply be powered by the first power source.

In such an arrangement, it may be deemed necessary or desirable to take the static transfer switch offline (e.g., for maintenance) while still providing power to the first load bus. To achieve this, the first load bus may be disconnected from the static transfer switch and connected to the second load bus by closing the bus tie breakers, after which the first load bus is powered via its connection to the second load bus. To ensure continuity of power to the loads connected to the first load bus, a closed-transition or make-before-break transfer procedure may be used to perform this operation. In accordance with such a procedure, the static transfer switch remains connected and supplies power to the first load bus until the second load bus is also connected to the first load bus via the closing of one or more of the bus tie breakers. After this, the static transfer switch is disconnected from the first load bus. To carry out the closed-transition procedure safely, it is critical to ensure that the first load bus and the second load bus are both being powered by the same power source before the bus tie breakers are closed.

SUMMARY

Key interlock systems and methods are described herein for safely carrying out a closed-transition or make-before-break procedure in an electric power distribution system that has a main-tie-tie-main or similar architecture and that utilizes at least one static transfer switch.

For example, the key interlock systems and methods described herein may be used to safely carry out a closed-transition procedure in an electric power distribution system in which two separately powered load busses that can be separately powered by the same power source or by two different power sources can be connected together via one or more bus tie breakers and in which a static transfer switch is used to selectively deliver power from one of the two different power sources to at least one of the load busses. Embodiments described herein prohibit access to a key that is required to close a bus tie breaker that connects the two load busses until at least a determination is made that a particular bypass breaker of the static transfer switch has been closed, thereby ensuring that both load busses are connected to the same power source. In embodiments, a solenoid key release unit that is integrated with the static transfer switch is energized when at least the bypass breaker is closed, thereby causing a key to be released from the solenoid key release unit that can then be used to obtain the key needed to close the bus tie breaker.

In accordance with further embodiments, switching logic of the static transfer switch is disabled when the key is removed from the solenoid key release unit, thereby providing a further safeguard against the inadvertent connection of two out of phase power sources together during the closed-transition procedure.

In accordance with still further embodiments, a key transfer block will only release the key required to close the bus tie breaker when it has at least captured the key removed from the solenoid key release unit and another key obtained from a key interlock device that has been manipulated by an operator to permit closing of the bypass breaker. By capturing the key obtained from the key interlock device, the key transfer block can prevent an operator from using that key to cause the static transfer switch to deliver power to the first load bus from a different power source than that being used to power the second load bus.

DETAILED DESCRIPTION

Key interlock systems and methods are described herein for safely carrying out a closed-transition or make-before-break procedure in an electric power distribution system that has a main-tie-tie-main or similar architecture and that utilizes at least one static transfer switch. To help illustrate the inventive key interlock systems and methods, Section II describes a first key interlock system and method and shortcomings thereof. Then, Section III describes various improved key interlock systems and methods. Section IV describes some additional exemplary embodiments. Finally, Section V provides some concluding remarks.

II. Exemplary First Key Interlock System and Method

FIG. 1is a block diagram of an electric power distribution system100that has a main-tie-tie-main configuration and a single static transfer switch. As will be described in this section, electric power distribution system100implements a key interlock scheme that is intended to ensure safe performance of a closed-transition procedure.

As shown inFIG. 1, electric power distribution system100includes a first power source102(also denoted “Source1”) and a second power source104(also denoted “Source2”). In one embodiment, first power source102comprises a primary uninterruptible power supply (UPS) and second power source104comprises an alternate UPS. However, this example is not intended to be limiting, and each of first power source102and second power source104may comprise other types of power sources including but not limited to utility power grids, generators (e.g., diesel or gas turbine generators), or battery banks. In an embodiment, first power source102and second power source104comprise AC power sources.

Electric power distribution system100also includes a static transfer switch106having a first power connection116, a second power connection118and a third power connection120. First power source102is connected to static transfer switch106via first power connection116. Second power source104is connected to static transfer switch106via second power connection118. Generally speaking, static transfer switch106can operate to distribute electric power supplied by either first power source102or second power source104to a first load bus110to which static transfer switch106is connected via third power connection120. More details concerning the manner of operation of static transfer switch106will be provided below.

A first transformer108is connected between third power connection120of static transfer switch106and first load bus110. First transformer108operates in a well-known manner to modify (e.g., step down) a voltage level of electricity supplied by static transfer switch106to a level that is suitable for loads that may be connected to first load bus110.

A main breaker122is connected between first transformer108and first load bus110. When closed, main breaker122enables electric power to be supplied from static transfer switch106to first load bus110. When open, main breaker122electrically isolates first load bus110from static transfer switch106.

A plurality of loads may be connected to first load bus110via a corresponding plurality of distribution breakers124,126,128and130. When closed, each of distribution breakers124,126,128and130enables power to be supplied from first load bus110to a respective load attached thereto. When open, each of distribution breakers124,126,128and130electrically isolates a respective load attached thereto from first load bus110.

As further shown inFIG. 1, first power source102is also connected to a second load bus114via a separate power distribution path. In particular, a second transformer112is connected between first power supply102and second load bus114. Second transformer112operates in a well-known manner to modify (e.g., step down) a voltage level of electricity supplied by first power source102to a level that is suitable for loads that may be connected to second load bus114.

A main breaker134is connected between second transformer112and second load bus114. When closed, main breaker134enables power to be supplied from first power source102to second load bus114. When open, main breaker134electrically isolates second load bus114from first power source102.

A plurality of loads may be connected to second load bus114via a corresponding plurality of distribution breakers136,138,140and142. When closed, each of distribution breakers136,138,140and142enables power to be supplied from second load bus114to a respective load attached thereto. When open, each of distribution breakers136,138,140and142electrically isolates a respective load attached thereto from second load bus114.

A first bus tie breaker132and a second bus tie breaker144are connected in series between first load bus110and a second load bus114. When first bus tie breaker132and second bus tie breaker144are both closed, first load bus110and second load bus114effectively become a single load bus to which power may be supplied via main breaker122, main breaker134, or both main breaker122and main breaker134. When either of first bus tie breaker132or second bus tie breaker144is open, first load bus110and second load bus114are electrically isolated from each other.

In electric power distribution system100, operator access to main breaker122, first bus tie breaker132, and distribution breakers124,126,128and130is provided via a first switchboard146. For example, an operator may interact with various switches on switchboard146to selectively open or close each of these breakers. Similarly, operator access to each of main breaker134, second bus tie breaker144, and distribution breakers136,138,140and142is provided via a second switchboard148. For example, an operator may interact with various switches on switchboard148to selectively open or close each of these breakers.

As further shown inFIG. 1, static transfer switch106includes switching logic150. First power source102is connected to switching logic150via first power connection116and second power source104is connected to switching logic150via second power connection118. Switching logic150includes a plurality of silicon-controlled rectifiers (SCRs), the gates of which can be automatically controlled by control logic within switching logic150(not shown inFIG. 1) to selectively cause power from first power source102or from second power source104to be supplied to first load bus110via third power connection120. For example, in one operational scenario, switching logic150may automatically switch from supplying power to first load bus110from first power source102to supplying power to first load bus110from second power source104in response to sensing that first power source102is not supplying power in accordance with certain operating parameters or requirements.

Static transfer switch106includes a number of circuit breakers. In particular, static transfer switch106includes a first source input breaker152, a second source input breaker154, a first load breaker156, a second load breaker158, a first bypass breaker160and a second bypass breaker162. An operator may open or close each of the circuit breakers to manually modify the manner of operation of static transfer switch106. In a state of operation in which switching logic150is enabled and intended to control the supply of power to first load bus110, first source input breaker152, second source input breaker154, first load breaker156and second load breaker158are closed and first bypass breaker160and second bypass breaker162are open.

Electric power distribution system100(and the other electric power distribution systems described herein) may be used in a data center to provide continuous and reliable power to a plurality of servers, such as a plurality of dual-corded servers. For example, each dual-corded server in the plurality of dual-corded servers may be connected via a first power cord to first load bus110and also connected via a second power cord to second load bus114. However, the electric power distribution systems described herein are not limited to data center operating environments and may advantageously be used to supply power to loads in other operating environments as well, and particularly those in which it is important to supply power to loads in a continuous and reliable manner (e.g., hospitals).

To enable maintenance to be performed on static transfer switch106(or for other reasons as well), it may be desired to take static transfer switch106offline while still providing power to first load bus110. To achieve this, first load bus110may be disconnected from static transfer switch106by opening main breaker122and by closing first bus tie breaker132and second bus tie breaker144(or closing one of those bus tie breakers if the other was already closed), after which first load bus110is powered via its connection to second load bus114. To ensure continuity of power to the loads connected to first load bus110, a closed-transition or make-before-break transfer procedure may be used to perform this operation. In accordance with such a procedure, static transfer switch106remains connected and supplies power to first load bus110until second load bus114is also connected to first load bus110via the closing of one or both of first bus tie breaker132and second bus tie breaker144. After this, static transfer switch106is disconnected from first load bus110.

To carry out the closed-transition procedure safely, it is desirable to ensure that first load bus110and second load bus114are both being powered by the same power source (in this case, first power source102) before first bus tie breaker132and second bus tie breaker144are closed. If first load bus110and second load bus114are being powered by different out-of-phase power sources when first bus tie breaker132and second bus tie breaker144are closed, then a fault condition may occur that can result in damage to and/or failure of equipment within electric power distribution system100and also create a significant safety hazard for people located closely thereto.

To avoid this, electric power distribution system100employs a key interlock system and method that is intended to prohibit access to a key that is necessary to close second bus tie breaker144until certain operating conditions have been met. The key interlock system and method utilized by electric power distribution system100is intended to require an operator to carry out a closed-transition procedure in a manner that avoids the closing of two out-of-phase power sources. However, as will be described below, this key interlock system and method has certain shortcomings.

In accordance with the key interlock system and method of electric power distribution system100, a first key interlock device164is mounted proximate to first bypass breaker160, a second key interlock device166is mounted proximate to second bypass breaker162, a third key interlock device168is mounted proximate to main breaker122, a fourth key interlock device170is mounted proximate to main breaker134, and a fifth key interlock device172is mounted proximate to second bus tie breaker144. The key interlock system and method further includes a first key (denoted “2K1” inFIG. 1) and first, second and third copies of a second key (denoted “2K3”).

First key interlock device164is operable to be transitioned from a first state to a second state using the first key (2K1). The first state of first key interlock device164comprises a state in which first key interlock device164impedes closing of first bypass breaker160, allows insertion and removal of the first key (2K1), and prevents removal of a copy of the second key (2K3). The second state of first key interlock device164comprises a state in which first key interlock device164does not impede the closing of first bypass breaker160, enables insertion and removal of the copy of the second key (2K3), and prevents removal of the first key (2K1).

For example, first key interlock device164may be implemented in a manner shown inFIG. 2. As illustrated in that figure, first key interlock device164may comprise a housing202, a first lock cylinder204, a second lock cylinder206, and a sliding lock bolt208. First lock cylinder204is configured to receive the first key (2K1) and is rotatable thereby to transition first key interlock device164from the first state to the second state. In particular, the rotation of first lock cylinder204using the first key (2K1) causes sliding lock bolt208to retract into housing202such that it does not physically impede the closing of first bypass breaker160. The rotation of first lock cylinder204using the first key (2K1) also causes second lock cylinder206to release the copy of the second key (2K3). Once first key interlock device164has been transitioned to the second state, the first key (2K1) may be captured in first lock cylinder204such that it cannot be removed from first key interlock device164.

Second lock cylinder206is configured to receive the copy of the second key (2K3) and is rotatable thereby to transition first key interlock device164from the second state to the first state. In particular, the rotation of second lock cylinder206using the copy of the second key (2K3) causes sliding lock bolt208to extend out of housing202such that it physically impedes the closing of first bypass breaker160. The rotation of second lock cylinder206using the second key (2K3) also causes first lock cylinder204to release the first key (2K1). Once first key interlock device164has been transitioned to the first state, the copy of the second key (2K3) may be captured in second lock cylinder206such that it cannot be removed from first key interlock device164.

Second key interlock device166is operable to be transitioned from a first state to a second state using the first key (2K1). The first state of second key interlock device166comprises a state in which second key interlock device166impedes closing of second bypass breaker162and allows insertion and removal of the first key (2K1). The second state of second key interlock device166comprises a state in which second key interlock device166does not impede the closing of second bypass breaker162and prevents removal of the first key (2K1) from second key interlock device166.

For example, second key interlock device166may be implemented in a manner shown inFIG. 3. As illustrated in that figure, second key interlock device166may comprise a housing302, a lock cylinder304, and a sliding lock bolt306. Lock cylinder304is configured to receive the first key (2K1) and is rotatable thereby in a first direction to transition second key interlock device166from the first state to the second state. In particular, the rotation of lock cylinder304using the first key (2K1) in a first direction causes sliding lock bolt306to retract into housing302such that it does not physically impede the closing of second bypass breaker162. Once second key interlock device166has been transitioned to the second state, the first key (2K1) may be captured in lock cylinder304such that it cannot be removed from second key interlock device166. Lock cylinder304is also rotatable by the first key (2K1) in a second direction to transition second key interlock device166from the second state to the first state. In particular, the rotation of lock cylinder304using the first key (2K1) in a second direction causes sliding lock bolt306to slide or extend out of housing302such that it physically impedes the closing of second bypass breaker162. The rotation of lock cylinder304in the second direction using the first key (2K1) also causes lock cylinder304to release the first key (2K1).

Third key interlock device168is operable to be transitioned from a first state to a second state using a copy of the second key (2K3). The first state of third key interlock device168comprises a state in which third key interlock device168impedes closing of main breaker122and allows insertion and removal of the copy of the second key (2K3). The second state of third key interlock device168comprises a state in which third key interlock device168does not impede the closing of main breaker122and prevents removal of the copy of the second key (2K3) from third key interlock device168. Third key interlock device168may be of a same or similar design as second key interlock device166as described above in reference toFIG. 3.

Fourth key interlock device170is operable to be transitioned from a first state to a second state using a copy of the second key (2K3). The first state of fourth key interlock device170comprises a state in which fourth key interlock device170impedes closing of main breaker134and allows insertion and removal of the copy of the second key (2K3). The second state of fourth key interlock device170comprises a state in which fourth key interlock device170does not impede the closing of main breaker134and prevents removal of the copy of the second key (2K3) from fourth key interlock device170. Fourth key interlock device170may be of a same or similar design as second key interlock device166as described above in reference toFIG. 3.

Fifth key interlock device172is operable to be transitioned from a first state to a second state using a copy of the second key (2K3). The first state of fifth key interlock device172comprises a state in which fifth key interlock device172impedes closing of second bus tie breaker144and allows insertion and removal of the copy of the second key (2K3). The second state of fifth key interlock device172comprises a state in which fifth key interlock device172does not impede the closing of second bus tie breaker144and prevents removal of the copy of the second key (2K3) from fifth key interlock device172. Fifth key interlock device172may be of a same or similar design as second key interlock device166as described above in reference toFIG. 3.

A closed-transition procedure in accordance with the key interlock system and method implemented by electric power distribution system100will now be described. For the purpose of this explanation, it will be assumed that the following operational state exists before an operator initiates the closed-transition procedure:With respect to static transfer switch106: first source input breaker152, second source input breaker154, first load breaker156, and second load breaker158are closed, while first bypass breaker160and second bypass breaker162are open;First key interlock device164is in its first state (impeding the closing of first bypass breaker160, allowing insertion and removal of the first key (2K1), and preventing removal of a copy of the second key (2K3));Second key interlock device166is in its first state (impeding the closing of second bypass breaker162and allowing insertion and removal of the first key (2K1));With respect to first switchboard146: main breaker122, first bus tie breaker132, and distribution breakers124,126,128and130are all closed;Third key interlock device168is in its second state (not impeding the closing of main breaker122and preventing removal of a copy of the second key (2K3))With respect to second switchboard148: main breaker134and distribution breakers136,138,140and142are closed, while second bus tie breaker144is open;Fourth key interlock device170is in its second state (not impeding the closing of main breaker134and preventing removal of a copy of the second key (2K3)); andFifth key interlock device172is in its first state (impeding the closing of second bus tie breaker144and allowing insertion and removal of a copy of the second key (2K3)).

Thus, in accordance with this initial operating state, static transfer switch106is selectively supplying power to first load bus110from one of first power source102or second power source104, first power source102is supplying power to second load bus114, and first load bus110and second load bus114are not electrically connected because second bus tie breaker144is open.

Furthermore, in accordance with this initial operating state, the first key (2K1) is available for use by the operator, while all three copies of the second key (2K3) are captured—one by first key interlock device164, one by third key interlock device168, and one by fourth key interlock device170. Thus, the operator cannot currently close second bus tie breaker144since there are no copies of the second key (2K3) available to change the state of fifth key interlock device172such that it is not impeding the closing of that breaker.

To perform the closed-transition procedure, the operator first opens second source input breaker154.

Then, the operator uses the first key (2K1) to transition first key interlock device164from its first state to its second state. At this point, first key interlock device164no longer impedes the closing of first bypass breaker164and also allows removal of a copy of the second key (2K3).

The operator then closes first bypass breaker160. This, along with the opening of second source input breaker154, ensures that power is being supplied to first load bus110by first power source102, which is the same power source that is supplying power to second load bus114.

The operator then takes the copy of the second key (2K3) that was released from first key interlock device164and uses it to transition fifth key interlock device172from its first state to its second state. At this point, fifth key interlock device172is not impeding the closing of second bus tie breaker144.

The operator then closes second bus tie breaker144, thereby electrically connecting first load bus110to second load bus114while they are both being powered by the same power source. After this point, static transfer switch106can be disconnected from first load bus110(e.g., by transitioning third key interlock device168from its second state to its first state and then opening main breaker122) without any discontinuity of power to the loads connected to first load bus110.

A significant safety issue exists in the foregoing key interlock system and method—namely, there is nothing that requires the operator to open second source input breaker154or close first bypass breaker160before closing second bus tie breaker144. The operator is only required to enable first bypass breaker160to be closed. Consequently, the operator can potentially close second bus tie breaker144while second source input breaker154is closed, first bypass breaker160is open, and static transfer switch106is supplying power to first load bus110from second power source104. As mentioned above, if second power source104is out of phase with first power source102, then closing second bus tie breaker144at such a time could result in damage to and/or failure of equipment within electric power distribution system100and also create a safety hazard for people located closely thereto. Various key interlock systems and methods that address this safety issue will be described in the following section.

III. Exemplary Improved Key Interlock Systems and Methods

FIG. 4is a block diagram of an electric power distribution system400that has a main-tie-tie-main configuration and a single static transfer switch. As will be described in this section, electric power distribution system400implements an improved key interlock scheme that is intended to ensure safe performance of a closed-transition procedure in a manner that addresses certain safety issues present in the key interlock scheme discussed in the preceding section.

Electric power distribution system400has a substantially similar architecture to electric power distribution system100as discussed above in reference toFIG. 1. Thus, for the sake of brevity, it suffices to state that electric power distribution system400includes a first power source402, a second power source404, a first transformer408, a first load bus410, a second load bus414, and a second transformer412that may be structurally, functionally and/or operationally equivalent to first power source102, second power source104, first transformer108, first load bus110, second load bus114, and second transformer112, respectively, of electric power distribution system100.

Furthermore, static transfer switch406includes a first power connection416, a second power connection418, a third power connection420, switching logic450, a first source input breaker452, a second source input breaker454, a first load breaker456, a second load breaker458, a first bypass breaker460and a second bypass breaker462that may be structurally, functionally and/or operationally equivalent to first power connection116, second power connection118, third power connection120, switching logic150, first source input breaker152, second source input breaker154, first load breaker156, second load breaker158, first bypass breaker160and second bypass breaker162, respectively, of static transfer switch106.

Still further, electric power distribution system400includes a first switchboard446, a main breaker422, distribution breakers424,426,428,430, a first bus tie breaker432, a second switchboard448, a second main breaker434, distribution breakers436,438,440,442, and a second bus tie breaker444that may be structurally, functionally and/or operationally equivalent to first switchboard146, main breaker122, distribution breakers124,126,128,130, first bus tie breaker132, second switchboard148, second main breaker134, distribution breakers136,138,140,142and second bus tie breaker144, respectively, of electric power distribution system100.

For reasons previously discussed, it may be desired to perform a closed-transition procedure in a manner that ensures that first load bus410and second load bus414are both being powered by the same power source (in this case, first power source402) before first bus tie breaker432and second bus tie breaker444are closed. To help achieve this, electric power distribution system400employs a key interlock system and method that prohibits access to a key that is required to close second bus tie breaker444until at least a determination is made that first bypass breaker460of static transfer switch406has been closed. As will be discussed below, a solenoid key release unit474that is integrated with static transfer switch406is energized when at least first bypass breaker460is closed, thereby causing a key to be released from solenoid key release unit474that can then be used to obtain the key needed to close second bus tie breaker444.

In accordance with the key interlock system and method of electric power distribution system400, a first key interlock device464is mounted proximate to first bypass breaker460, a second key interlock device466is mounted proximate to second bypass breaker462, a third key interlock device468is mounted proximate to main breaker422, a fourth key interlock device470is mounted proximate to main breaker434, and a fifth key interlock device472is mounted proximate to second bus tie breaker444. The key interlock system and method further includes a solenoid key release unit474, a key transfer block476, a first key (denoted “2K1” inFIG. 4), a second key (denoted “2K3” inFIG. 4), a third key (denoted “K6” inFIG. 4), and first, second and third copies of a fourth key (denoted “2K5” inFIG. 4).

First key interlock device464is operable to be transitioned from a first state to a second state using the first key (2K1). The first state of first key interlock device464comprises a state in which first key interlock device464impedes closing of first bypass breaker460, allows insertion and removal of the first key (2K1), and prevents removal of the second key (2K3). The second state of first key interlock device464comprises a state in which first key interlock device464does not impede the closing of first bypass breaker460, enables insertion and removal of the second key (2K3), and prevents removal of the first key (2K1). First key interlock device464may be of a same or similar design as first key interlock device164as described above in reference toFIG. 2.

Second key interlock device466is operable to be transitioned from a first state to a second state using the first key (2K1). The first state of second key interlock device466comprises a state in which second key interlock device466impedes closing of second bypass breaker462and allows insertion and removal of the first key (2K1). The second state of second key interlock device466comprises a state in which second key interlock device466does not impede the closing of second bypass breaker462and prevents removal of the first key (2K1) from second key interlock device466. Second key interlock device466may be of a same or similar design as second key interlock device166as described above in reference toFIG. 3.

Third key interlock device468is operable to be transitioned from a first state to a second state using a copy of the fourth key (2K5). The first state of third key interlock device468comprises a state in which third key interlock device468impedes closing of main breaker422and allows insertion and removal of the copy of the fourth key (2K5). The second state of third key interlock device468comprises a state in which third key interlock device468does not impede the closing of main breaker422and prevents removal of the copy of the fourth key (2K5) from third key interlock device468. Third key interlock device468may be of a same or similar design as second key interlock device166as described above in reference toFIG. 3.

Fourth key interlock device470is operable to be transitioned from a first state to a second state using a copy of the fourth key (2K5). The first state of fourth key interlock device470comprises a state in which fourth key interlock device470impedes closing of main breaker434and allows insertion and removal of the copy of the fourth key (2K5). The second state of fourth key interlock device470comprises a state in which fourth key interlock device470does not impede the closing of main breaker434and prevents removal of the copy of the fourth key (2K5) from fourth key interlock device470. Fourth key interlock device470may be of a same or similar design as second key interlock device166as described above in reference toFIG. 3.

Fifth key interlock device472is operable to be transitioned from a first state to a second state using a copy of the fourth key (2K5). The first state of fifth key interlock device472comprises a state in which fifth key interlock device472impedes closing of second bus tie breaker444and allows insertion and removal of the copy of the fourth key (2K5). The second state of fifth key interlock device472comprises a state in which fifth key interlock device472does not impede the closing of second bus tie breaker444and prevents removal of the copy of the fourth key (2K5) from fifth key interlock device472. Fifth key interlock device472may be of a same or similar design as second key interlock device166as described above in reference toFIG. 3.

Solenoid key release unit474is a component that is integrated with static transfer switch406and that is operable to be placed in a non-energized state when at least first bypass breaker460is open and to be placed in an energized state when at least first bypass breaker460is closed. When in the non-energized state, solenoid key release unit474prevents removal of the third key (K6) therefrom. When in the energized state, solenoid key release unit474enables removal of the third key (K6) therefrom.

In an embodiment, solenoid key release unit474is configured to release the third key (K6) only when first bypass breaker460is closed and an operator has also pressed a push button associated with solenoid key release unit474.FIG. 5is a diagram of solenoid key release unit474and associated activation logic that may be used in such an embodiment.

As shown inFIG. 5, solenoid key release unit474is connected to a first terminal of an uninterruptible power source502and is also connected to a push button506. Push button506is further connected to an auxiliary contact504that is linked to first bypass breaker460in a well-known manner. Auxiliary contact504is further connected to a second terminal of uninterruptible power source502. As further shown inFIG. 5, a pilot light508is connected to the first terminal of uninterruptible power source502and is also connected to auxiliary contact504. In one embodiment, uninterruptible power source502comprises a 125 VDC station battery, although other types of power sources may be used. In an embodiment, a power source that is different than first power source402and second power source404is utilized to energize solenoid key release unit474.

The manner of operation of the logic shown inFIG. 5will now be described. When first bypass breaker460is open, then auxiliary contact504will also be open, which means that solenoid key release unit474cannot be energized (regardless of the state of push button506) and pilot light508will be off. When first bypass breaker460is closed, then auxiliary contact504will also be closed, which means that pilot light508will be powered by uninterruptible power source502and will turn on (i.e., be lit). This activation of pilot light508is intended to provide an extra indication to an operator that first bypass breaker460is closed. While first bypass breaker460is closed and push button506is not being pressed, solenoid key release unit474still cannot be energized due to the configuration of the logic shown inFIG. 5. However, if first bypass breaker460is closed and an operator presses push button506, then solenoid key release unit474will be energized by uninterruptible power source502and release the third key (K6). By requiring the operator to press push button506to energize solenoid key release unit474and release the third key (K6) when first bypass breaker460is closed, the logic shown inFIG. 5advantageously limits the amount of power that can be consumed by solenoid key release unit474while first bypass breaker502is closed.

In a further embodiment depicted inFIG. 6, solenoid key release unit474is further connected to static transfer switch disabling logic602. In accordance with such an embodiment, when the third key (K6) is removed from solenoid key release unit474, solenoid key release unit474detects this and sends an input signal to static transfer switch disabling logic602that causes such logic to disable the operation of switching logic450. This provides yet another safeguard for ensuring that first load bus410is not being powered by second power source404when second bus tie breaker444is closed.

Returning now to the description ofFIG. 4, key transfer block476comprises a component that is operable to be transitioned from a first state to a second state using both the second key (2K3) and the third key (K6). The first state of key transfer block476comprises a state in which key transfer block476prevents removal of a copy of the fourth key (2K5) therefrom and the second state of key transfer block476comprises a state in which key transfer block476enables removal of the copy of fourth key (2K5) therefrom.

For example, key transfer block476may be implemented in a manner shown inFIG. 7. As illustrated in that figure, key transfer block476may comprise a housing702, a first lock cylinder704, a second lock cylinder706, and a third lock cylinder708. First lock cylinder704is configured to receive the second key (2K3) and is rotatable thereby. Second lock cylinder706is configured to receive the third key (K6) and is rotatable thereby. When both first lock cylinder704and second lock cylinder706have been rotated by their respective keys, then key transfer block476will be placed in a state in which a copy of the fourth key (2K5) will be released from third lock cylinder708. Thus, both the second key (2K3) and the third key (K6) are required to access the copy of the fourth key (2K5) that is held by key transfer block476.

A closed-transition procedure in accordance with the key interlock system and method implemented by electric power distribution system400will now be described. For the purpose of this explanation, it will be assumed that the following operational state exists before an operator initiates the closed-transition procedure:With respect to static transfer switch406: first source input breaker452, second source input breaker454, first load breaker456, and second load breaker458are closed, while first bypass breaker460and second bypass breaker462are open;First key interlock device464is in its first state (impeding the closing of first bypass breaker460, allowing insertion and removal of the first key (2K1), and preventing removal of the second key (2K3));Second key interlock device466is in its first state (impeding the closing of second bypass breaker462and allowing insertion and removal of the first key (2K1));Since first bypass breaker460is open, the third key (K6) is captured by solenoid key release unit474such that it cannot be removed therefrom;A copy of the fourth key (2K5) is captured by key transfer block476such that it cannot be removed therefrom;With respect to first switchboard446: main breaker422, first bus tie breaker432, and distribution breakers424,426,428and430are all closed;Third key interlock device468is in its second state (not impeding the closing of main breaker422and preventing removal of a copy of the fourth key (2K5));With respect to second switchboard448: main breaker434and distribution breakers436,438,440and442are closed, while second bus tie breaker444is open;Fourth key interlock device470is in its second state (not impeding the closing of main breaker434and preventing removal of a copy of the fourth key (2K5)); andFifth key interlock device472is in its first state (impeding the closing of second bus tie breaker444and allowing insertion and removal of a copy of the fourth key (2K5)).

Thus, in accordance with this initial operating state, static transfer switch406is selectively supplying power to first load bus410from one of first power source402or second power source404, first power source402is supplying power to second load bus414, and first load bus410and second load bus414are not electrically connected because second bus tie breaker444is open.

Furthermore, in accordance with this initial operating state, the first key (2K1) is available for use by the operator, while the second key (2K3) is captured by first interlock device464, the third key (K6) is captured by solenoid key release unit474, and all three copies of the fourth key (2K5) are captured—one by key transfer block476, one by third key interlock device468, and one by fourth key interlock device470. Thus, the operator cannot currently close second bus tie breaker444since there are no copies of the fourth key (2K5) available to change the state of fifth key interlock device472such that it is not impeding the closing of that breaker.

A method for performing a closed-transition procedure in accordance with the key interlock system described above in reference toFIG. 4will now be described in reference to flowchart800ofFIG. 8.

At step802, the operator opens second source input breaker454.

At step804, the operator uses the first key (2K1) to transition first key interlock device464from its first state to its second state. At this point, first key interlock device464no longer impedes the closing of first bypass breaker460and also allows removal of the second key (2K3).

At step806, the operator closes first bypass breaker460. As noted above, in an embodiment, this causes a pilot light (e.g., pilot light508) to be turned on. The turning on of the pilot light serves as a confirmation to the operator that first bypass breaker460is closed and also indicates to the operator that the third key (K6) can be removed from solenoid key release unit474by pressing a push button (e.g., push button506).

At step808, the operator presses the push button (e.g., push button506) which causes the third key (K6) to be released by solenoid key release unit474.

At step810, the operator uses the second key (2K3) and the third key (K6) to transition key transfer block476to a state in which a copy of the fourth key (2K5) can be removed therefrom.

At step812, the operator then takes the copy of the fourth key (2K5) that was released from key transfer block476and uses it to transition fifth key interlock device472from its first state to its second state. At this point, fifth key interlock device472is not impeding the closing of second bus tie breaker444.

At step814, the operator then closes second bus tie breaker444, thereby electrically connecting first load bus410to second load bus414while they are both being powered by the same power source. After this point, static transfer switch406can be disconnected from first load bus410(e.g., by transitioning third key interlock device468from its second state to its first state and then opening main breaker422) without any discontinuity of power to the loads connected to first load bus410.

The foregoing key interlock system and method improves upon that described in the previous section in a number of ways. For example, since key transfer block476will not release the copy of the fourth key (2K5) required to close second bus tie breaker444without first receiving the third key (K6), and since the third key (K6) will not be released by solenoid key release unit474until first bypass breaker460is closed, this key interlock system and method ensures that first bypass breaker460has been closed before the operator is permitted to close second bus tie breaker444. Furthermore, since key transfer block476also captures the second key (2K3) that was released by first key interlock device464, this key interlock system and method ensures that the operator cannot close second bus tie breaker444and then use the second key (2K3) to go back and open first bypass breaker460and then possibly close second bypass breaker466. Additionally, since the removal of the third key (K6) causes switching logic450of static transfer switch406to be disabled, this provides a further safeguard for ensuring that first load bus410is not being powered by second power source404when second bus tie breaker444is closed.

A variant of the foregoing key interlock system and method that can be used in electric power distribution systems having a main-tie-tie-main or similar configuration and two static transfer switches will now be described in reference toFIG. 9. In particular,FIG. 9is a block diagram of an electric power distribution system900that has a main-tie-tie-main configuration and two static transfer switches.

Electric power distribution system900includes a first power source902, a second power source904, a first static transfer switch906, a first transformer908, a first load bus910, a second static transfer switch981, a second transformer912, and a second load bus914. First power source902, second power source904, first transformer908, first load bus910, second transformer912and second load bus914may be structurally, functionally and/or operationally equivalent to first power source402, second power source404, first transformer408, first load bus410, second transformer412, and second load bus414, respectively, of electric power distribution system400.

First static transfer switch906includes a first power connection916, a second power connection918, a third power connection920, switching logic950, a first source input breaker952, a second source input breaker954, a first load breaker956, a second load breaker958, a first bypass breaker960and a second bypass breaker962that may be structurally, functionally and/or operationally equivalent to first power connection416, second power connection418, third power connection420, switching logic450, first source input breaker452, second source input breaker454, first load breaker456, second load breaker458, first bypass breaker460and second bypass breaker462, respectively, of static transfer switch406. Generally speaking, first static transfer switch906can operate to distribute electric power supplied by either first power source902or second power source904to first load bus910to which first static transfer switch906is connected via third power connection920.

Second static transfer switch981includes a first power connection983, a second power connection985, a third power connection987, switching logic982, a first source input breaker984, a second source input breaker986, a first load breaker988, a second load breaker990, a first bypass breaker992and a second bypass breaker994that may be structurally, functionally and operationally equivalent to first power connection416, second power connection418, third power connection420, switching logic450, first source input breaker452, second source input breaker454, first load breaker456, second load breaker458, first bypass breaker460and second bypass breaker462, respectively, of static transfer switch406. Generally speaking, second static transfer switch981can operate to distribute electric power supplied by either first power source902or second power source904to second load bus914to which second static transfer switch981is connected via third power connection987.

Electric power distribution system900also includes a first switchboard946, a main breaker922, distribution breakers924,926,928,930, a first bus tie breaker932, a second switchboard948, a second main breaker934, distribution breakers936,938,940,942, and a second bus tie breaker944which may be structurally, functionally and/or operationally equivalent to first switchboard446, main breaker422, distribution breakers424,426,428,430, first bus tie breaker432, second switchboard448, second main breaker434, distribution breakers436,438,440,442and second bus tie breaker444, respectively, of electric power distribution system400.

It may be desired to perform a closed-transition procedure in a manner that ensures that first load bus910and second load bus914are both being powered by the same power source (in this case, either first power source902or second power source904) before first bus tie breaker932and second bus tie breaker944are closed. To help achieve this, electric power distribution system900employs a key interlock system and method that prohibits access to a key that is required to close second bus tie breaker944until at least a determination is made that either (a) first bypass breaker960of first static transfer switch906has been closed and first bypass breaker992of second static transfer switch981has been closed, or (b) second bypass breaker962of first static transfer switch906has been closed and second bypass breaker994of second static transfer switch981has been closed.

In accordance with the key interlock system and method of electric power distribution system900, a first key interlock device964is mounted proximate to first bypass breaker960, a second key interlock device966is mounted proximate to second bypass breaker962, a third key interlock device996is mounted proximate to first bypass breaker992, a fourth key interlock device997is mounted proximate to second bypass breaker994, a fifth key interlock device968is mounted proximate to main breaker922, a sixth key interlock device970is mounted proximate to main breaker934, and a seventh key interlock device972is mounted proximate to second bus tie breaker944. The key interlock system and method further includes a solenoid key release unit974, a solenoid key release unit976, a solenoid key release unit998, a solenoid key release unit999, a key transfer block978, a key transfer block980, a first key (denoted “2K1” inFIG. 9), a second key (denoted “2K2” inFIG. 9), two copies of a third key (denoted “2K3” inFIG. 9), two copies of a fourth key (denoted “2K4” inFIG. 9), two copies of a fifth key (denoted “K6” inFIG. 9), two copies of a sixth key (denoted “K7” inFIG. 9), and first, second, third and fourth copies of a seventh key (denoted “2K5” inFIG. 9).

First key interlock device964is operable to be transitioned from a first state to a second state using the first key (2K1). The first state of first key interlock device964comprises a state in which first key interlock device964impedes closing of first bypass breaker960, allows insertion and removal of the first key (2K1), and prevents removal of a copy of the third key (2K3). The second state of first key interlock device964comprises a state in which first key interlock device964does not impede the closing of first bypass breaker960, enables insertion and removal of the copy of the third key (2K3), and prevents removal of the first key (2K1). First key interlock device964may be of a same or similar design as first key interlock device164as described above in reference toFIG. 2.

Second key interlock device966is operable to be transitioned from a first state to a second state using the first key (2K1). The first state of second key interlock device966comprises a state in which second key interlock device966impedes closing of second bypass breaker962, allows insertion and removal of the first key (2K1), and prevents removal of a copy of the fourth key (2K4). The second state of second key interlock device966comprises a state in which second key interlock device966does not impede the closing of second bypass breaker962, enables insertion and removal of the copy of the fourth key (2K4), and prevents removal of the first key (2K1). Second key interlock device966may be of a same or similar design as first key interlock device164as described above in reference toFIG. 2.

Third key interlock device996is operable to be transitioned from a first state to a second state using the second key (2K2). The first state of third key interlock device996comprises a state in which third key interlock device996impedes closing of first bypass breaker992, allows insertion and removal of the second key (2K2), and prevents removal of a copy of the third key (2K3). The second state of third key interlock device996comprises a state in which third key interlock device996does not impede the closing of first bypass breaker992, enables insertion and removal of the copy of the third key (2K3), and prevents removal of the second key (2K2). Third key interlock device996may be of a same or similar design as first key interlock device164as described above in reference toFIG. 2.

Fourth key interlock device997is operable to be transitioned from a first state to a second state using the second key (2K2). The first state of fourth key interlock device997comprises a state in which fourth key interlock device997impedes closing of second bypass breaker994, allows insertion and removal of the second key (2K2), and prevents removal of a copy of the fourth key (2K4). The second state of fourth key interlock device997comprises a state in which fourth key interlock device997does not impede the closing of second bypass breaker994, enables insertion and removal of the copy of the fourth key (2K4), and prevents removal of the second key (2K2). Fourth key interlock device997may be of a same or similar design as first key interlock device164as described above in reference toFIG. 2.

Fifth key interlock device968is operable to be transitioned from a first state to a second state using a copy of the seventh key (2K5). The first state of fifth key interlock device968comprises a state in which fifth key interlock device968impedes closing of main breaker922and allows insertion and removal of the copy of the seventh key (2K5). The second state of fifth key interlock device968comprises a state in which fifth key interlock device968does not impede the closing of main breaker922and prevents removal of the copy of the seventh key (2K5) from fifth key interlock device968. Fifth key interlock device968may be of a same or similar design as second key interlock device166as described above in reference toFIG. 3.

Sixth key interlock device970is operable to be transitioned from a first state to a second state using a copy of the seventh key (2K5). The first state of sixth key interlock device970comprises a state in which sixth key interlock device970impedes closing of main breaker934and allows insertion and removal of the copy of the seventh key (2K5). The second state of sixth key interlock device970comprises a state in which sixth key interlock device970does not impede the closing of main breaker934and prevents removal of the copy of the seventh key (2K5) from sixth key interlock device970. Sixth key interlock device970may be of a same or similar design as second key interlock device166as described above in reference toFIG. 3.

Seventh key interlock device972is operable to be transitioned from a first state to a second state using a copy of the seventh key (2K5). The first state of seventh key interlock device972comprises a state in which seventh key interlock device972impedes closing of second bus tie breaker944and allows insertion and removal of the copy of the seventh key (2K5). The second state of seventh key interlock device972comprises a state in which seventh key interlock device972does not impede the closing of second bus tie breaker944and prevents removal of the copy of the seventh key (2K5) from seventh key interlock device972. Seventh key interlock device972may be of a same or similar design as second key interlock device166as described above in reference toFIG. 3.

Solenoid key release unit974is a component that is integrated with first static transfer switch906and that is operable to be placed in a non-energized state when at least first bypass breaker960is open and to be placed in an energized state when at least first bypass breaker960is closed. When in the non-energized state, solenoid key release unit974prevents removal of a copy of the fifth key (K6) therefrom. When in the energized state, solenoid key release unit974enables removal of the copy of the fifth key (K6) therefrom.

Solenoid key release unit976is a component that is integrated with first static transfer switch906and that is operable to be placed in a non-energized state when at least second bypass breaker962is open and to be placed in an energized state when at least second bypass breaker962is closed. When in the non-energized state, solenoid key release unit976prevents removal of a copy of the sixth key (K7) therefrom. When in the energized state, solenoid key release unit976enables removal of the copy of the sixth key (K7) therefrom.

Solenoid key release unit998is a component that is integrated with second static transfer switch981and that is operable to be placed in a non-energized state when at least first bypass breaker992is open and to be placed in an energized state when at least first bypass breaker992is closed. When in the non-energized state, solenoid key release unit998prevents removal of a copy of the fifth key (K6) therefrom. When in the energized state, solenoid key release unit998enables removal of the copy of the fifth key (K6) therefrom.

Solenoid key release unit999is a component that is integrated with second static transfer switch981and that is operable to be placed in a non-energized state when at least second bypass breaker994is open and to be placed in an energized state when at least second bypass breaker994is closed. When in the non-energized state, solenoid key release unit999prevents removal of a copy of the sixth key (K7) therefrom. When in the energized state, solenoid key release unit999enables removal of the copy of the sixth key (K7) therefrom.

In an embodiment, solenoid key release unit974is configured to release the copy of the fifth key (K6) only when first bypass breaker960is closed and an operator has also pressed a push button associated with solenoid key release unit974and solenoid key release unit976is configured to release the copy of the sixth key (K7) only when second bypass breaker962is closed and an operator has also pressed a push button associated with solenoid key release unit976.FIG. 10is a diagram of solenoid key release units974,976and associated activation logic that may be used in such an embodiment.

As shown inFIG. 10, solenoid key release unit974is connected to a first terminal of an uninterruptible power source1002and is also connected to a push button1006. Push button1006is further connected to an auxiliary contact1004that is linked to first bypass breaker960in a well-known manner. Auxiliary contact1004is further connected to a second terminal of uninterruptible power source1002. A pilot light1008is connected to the first terminal of uninterruptible power source1002and is also connected to auxiliary contact1004. As further shown inFIG. 10, solenoid key release unit976is connected to the first terminal of uninterruptible power source1002and is also connected to a push button1012. Push button1012is further connected to an auxiliary contact1010that is linked to second bypass breaker962in a well-known manner. Auxiliary contact1010is further connected to the second terminal of uninterruptible power source1002. A pilot light1014is connected to the first terminal of battery1002and is also connected to auxiliary contact1010.

In one embodiment, uninterruptible power source1002comprises a125VDC station battery, although other types of power sources may be used. In an embodiment, a power source that is different than first power source902and second power source904is utilized to energize solenoid key release units974,976. Furthermore, although only a single power source is shown inFIG. 10, in alternate embodiments different power sources may be used to energize solenoid key release units974,976.

The manner of operation of the logic shown inFIG. 10will now be described. When first bypass breaker960is open, then auxiliary contact1004will also be open, which means that solenoid key release unit974cannot be energized (regardless of the state of push button1006) and pilot light1008will be off. When first bypass breaker960is closed, then auxiliary contact1004will also be closed, which means that pilot light1008will be powered by uninterruptible power source1002and will turn on (i.e., be lit). This activation of pilot light1008is intended to provide an extra indication to an operator that first bypass breaker960is closed. While first bypass breaker960is closed and push button1006is not being pressed, solenoid key release unit974still cannot be energized due to the configuration of the logic shown inFIG. 10. However, if first bypass breaker960is closed and an operator presses push button1006, then solenoid key release unit974will be energized by uninterruptible power source1002and release the copy of the fifth key (K6).

When second bypass breaker962is open, then auxiliary contact1010will also be open, which means that solenoid key release unit976cannot be energized (regardless of the state of push button1012) and pilot light1014will be off. When second bypass breaker962is closed, then auxiliary contact1010will also be closed, which means that pilot light1014will be powered by uninterruptible power source1002and will turn on (i.e., be lit). This activation of pilot light1014is intended to provide an extra indication to an operator that second bypass breaker962is closed. While second bypass breaker962is closed and push button1012is not being pressed, solenoid key release unit976still cannot be energized due to the configuration of the logic shown inFIG. 10. However, if second bypass breaker962is closed and an operator presses push button1012, then solenoid key release unit976will be energized by uninterruptible power source1002and release the copy of the fourth key (K7).

Using similar logic to that shown inFIG. 10, solenoid key release unit998may configured to release the copy of the fifth key (K6) only when first bypass breaker992is closed and an operator has also pressed a push button associated with solenoid key release unit998and solenoid key release unit999may be configured to release the copy of the sixth key (K7) only when second bypass breaker994is closed and an operator has also pressed a push button associated with solenoid key release unit999.

In a further embodiment depicted inFIG. 11, solenoid key release unit974and solenoid key release unit976are further connected to static transfer switch disabling logic1102. In accordance with such an embodiment, when the copy of the fifth key (K6) is removed from solenoid key release unit974, solenoid key release unit974detects this and sends an input signal to static transfer switch disabling logic1102that causes such logic to disable the operation of switching logic950. Likewise, when the copy of the sixth key (K7) is removed from solenoid key release unit976, solenoid key release unit976detects this and sends an input signal to static transfer switch disabling logic1102that causes such logic to disable the operation of switching logic950.

Using similar logic to that shown inFIG. 11, second static transfer switch981may be configured such that when the copy of the fifth key (K6) is removed from solenoid key release unit998, solenoid key release unit998sends an input signal to static transfer switch disabling logic that causes such logic to disable the operation of switching logic982. Likewise, second static transfer switch981may be configured such that when the copy of the sixth key (K7) is removed from solenoid key release unit999, solenoid key release unit999sends an input signal to static transfer switch disabling logic that causes such logic to disable the operation of switching logic982.

Returning now to the description ofFIG. 9, key transfer block978comprises a component that is operable to be transitioned from a first state to a second state using both copies of the third key (2K3) and both copies of the fifth key (K6). The first state of key transfer block978comprises a state in which key transfer block978prevents removal of a copy of the seventh key (2K5) therefrom and the second state of key transfer block978comprises a state in which key transfer block978enables removal of the copy of seventh key (2K5) therefrom.

For example, key transfer block978may be implemented in a manner shown inFIG. 12. As illustrated in that figure, key transfer block978may comprise a housing1202, a first lock cylinder1204, a second lock cylinder1206, a third lock cylinder1208, a fourth lock cylinder1210, and a fifth lock cylinder1212. First lock cylinder1204is configured to receive one copy of the third key (2K3) and is rotatable thereby. Second lock cylinder1206is configured to receive the other copy of the third key (2K3) and is rotatable thereby. Third lock cylinder1208is configured to receive one copy of the fifth key (K6) and is rotatable thereby. Fourth lock cylinder1210is configured to receive the other copy of the fifth key (K6) and is rotatable thereby. When first lock cylinder1204, second lock cylinder1206, third lock cylinder1208and fourth lock cylinder1210have been rotated by their respective keys, then key transfer block978will be placed in a state in which a copy of the seventh key (2K5) will be released from fifth lock cylinder1212. Thus, both copies of the third key (2K3) and both copies of the fifth key (K6) are required to access the copy of the seventh key (2K5) that is held by key transfer block978.

Key transfer block980comprises a component that is operable to be transitioned from a first state to a second state using both copies of the fourth key (2K4) and both copies of the sixth key (K7). The first state of key transfer block980comprises a state in which key transfer block980prevents removal of a copy of the seventh key (2K5) therefrom and the second state of key transfer block980comprises a state in which key transfer block978enables removal of the copy of seventh key (2K5) therefrom. Key transfer block980may be of a same or similar design as key transfer block978as described above in reference toFIG. 12.

Two closed-transition procedures in accordance with the key interlock system and method implemented by electric power distribution system400will now be described—one in which both load busses are connected to first power source902and another in which both load busses are connected to second power source904. For the purpose of this explanation, it will be assumed that the following operational state exists before an operator initiates either of the closed-transition procedures:With respect to first static transfer switch906: first source input breaker952, second source input breaker954, first load breaker956, and second load breaker958are closed, while first bypass breaker960and second bypass breaker962are open;First key interlock device964is in its first state (impeding the closing of first bypass breaker960, allowing insertion and removal of the first key (2K1), and preventing removal of a copy of the third key (2K3));Second key interlock device966is in its first state (impeding the closing of second bypass breaker962, allowing insertion and removal of the first key (2K1), and preventing removal of a copy of the fourth key (2K4));Since first bypass breaker960is open, a copy of the fifth key (K6) is captured by solenoid key release unit974such that it cannot be removed therefrom;Since second bypass breaker962is open, a copy of the sixth key (K7) is captured by solenoid key release unit976such that it cannot be removed therefrom;With respect to second static transfer switch981: first source input breaker984, second source input breaker986, first load breaker988, and second load breaker990are closed, while first bypass breaker992and second bypass breaker994are open;Third key interlock device996is in its first state (impeding the closing of first bypass breaker992, allowing insertion and removal of the second key (2K2), and preventing removal of a copy of the third key (2K3));Fourth key interlock device997is in its first state (impeding the closing of second bypass breaker994, allowing insertion and removal of the second key (2K2), and preventing removal of a copy of the fourth key (2K4));Since first bypass breaker992is open, a copy of the fifth key (K6) is captured by solenoid key release unit998such that it cannot be removed therefrom;Since second bypass breaker994is open, a copy of the sixth key (K7) is captured by solenoid key release unit999such that it cannot be removed therefrom;A copy of the seventh key (2K5) is captured by key transfer block978such that it cannot be removed therefrom;A copy of the seventh key (2K5) is captured by key transfer block980such that it cannot be removed therefrom;With respect to first switchboard946: main breaker922, first bus tie breaker932, and distribution breakers924,926,928and930are all closed;Fifth key interlock device968is in its second state (not impeding the closing of main breaker922and preventing removal of a copy of the seventh key (2K5));With respect to second switchboard948: main breaker934and distribution breakers936,938,940and942are closed, while second bus tie breaker944is open;Sixth key interlock device970is in its second state (not impeding the closing of main breaker934and preventing removal of a copy of the seventh key (2K5)); andSeventh key interlock device972is in its first state (impeding the closing of second bus tie breaker944and allowing insertion and removal of a copy of the seventh key (2K5)).

Thus, in accordance with this initial operating state, first static transfer switch906is selectively supplying power to first load bus910from one of first power source902or second power source904, second static transfer switch981is selectively supplying power to second load bus914from one of first power source902or second power source904, and first load bus910and second load bus914are not electrically connected because second bus tie breaker944is open.

Furthermore, in accordance with this initial operating state, the first key (2K1) and the second key (2K2) are both available for use by the operator, one copy of the third key (2K3) is captured by first interlock device964while the other copy of the third key (2K3) is captured by third interlock device996, one copy of the fourth key (2K4) is captured by second interlock device966while the other copy of the fourth key (2K4) is captured by fourth interlock device997, one copy of the fifth key (K6) is captured by solenoid key release unit974while the other copy of the fifth key (K6) is captured by solenoid key release unit998, one copy of the sixth key (K7) is captured by solenoid key release unit976while the other copy of the sixth key (K7) is captured by solenoid key release unit999, and all four copies of the seventh key (2K5) are captured—one by key transfer block978, one by key transfer block980, one by fifth key interlock device968, and one by sixth key interlock device970. Thus, the operator cannot currently close second bus tie breaker944since there are no copies of the seventh key (2K5) available to change the state of seventh key interlock device972such that it is not impeding the closing of that breaker.

A first method for performing a closed-transition procedure in accordance with the key interlock system described above in reference toFIG. 9will now be described in reference to flowchart1300ofFIG. 13.

At step1302, the operator opens second source input breaker954of first static transfer switch906.

At step1304, the operator uses the first key (2K1) to transition first key interlock device964from its first state to its second state. At this point, first key interlock device964no longer impedes the closing of first bypass breaker960of first static transfer switch906and also allows removal of a copy of the third key (2K3).

At step1306, the operator closes first bypass breaker960. As noted above, in an embodiment, this causes a pilot light associated with solenoid key release unit974to be turned on. The turning on of the pilot light serves as a confirmation to the operator that first bypass breaker960is closed and also indicates to the operator that a copy of the fifth key (K6) can be removed from solenoid key release unit974by pressing a push button.

At step1308, the operator presses the push button associated with solenoid key release unit974which causes the copy of the fifth key (K6) to be released by solenoid key release unit974.

At step1310, the operator opens second source input breaker986of second static transfer switch981.

At step1312, the operator uses the second key (2K2) to transition third key interlock device996from its first state to its second state. At this point, third key interlock device996no longer impedes the closing of first bypass breaker992of second static transfer switch981and also allows removal of a copy of the third key (2K3).

At step1314, the operator closes first bypass breaker992. As noted above, in an embodiment, this causes a pilot light associated with solenoid key release unit998to be turned on. The turning on of the pilot light serves as a confirmation to the operator that first bypass breaker992is closed and also indicates to the operator that a copy of the fifth key (K6) can be removed from solenoid key release unit998by pressing a push button.

At step1316, the operator presses the push button associated with solenoid key release unit998which causes the copy of the fifth key (K6) to be released by solenoid key release unit998.

At step1318, the operator uses the two copies of the third key (2K3) and the two copies of the fifth key (K6) to transition key transfer block978to a state in which a copy of the seventh key (2K5) can be removed therefrom.

At step1320, the operator then takes the copy of the seventh key (2K5) that was released from key transfer block978and uses it to transition seventh key interlock device972from its first state to its second state. At this point, seventh key interlock device972is not impeding the closing of second bus tie breaker944.

At step1322, the operator then closes second bus tie breaker944, thereby electrically connecting first load bus910to second load bus914while they are both being powered by first power source902. After this point, either first static transfer switch906can be disconnected from first load bus910(e.g., by transitioning fifth key interlock device968from its second state to its first state and then opening main breaker922) or second static transfer switch981can be disconnected from second load bus914(e.g., by transitioning sixth key interlock device970from its second state to its first state and then opening main breaker934) without any discontinuity of power to the loads connected to first load bus910or second load bus914.

In accordance with the foregoing key interlock system and method, since key transfer block978will not release the copy of the seventh key (2K5) required to close second bus tie breaker444without first receiving both copies of the fifth key (K6), and since both copies of the fifth key (K6) will not be released by solenoid key release units974,998until both first bypass breaker960and first bypass breaker992are closed, this key interlock system and method ensures that both first bypass breaker960and first bypass breaker992have been closed before the operator is permitted to close second bus tie breaker944. Furthermore, since key transfer block978also captures both copies of the third key (2K3), this key interlock system and method ensures that the operator cannot close second bus tie breaker944and then use the copies of the third key (2K3) to go back and open first bypass breaker960or first bypass breaker992and possibly close second bypass breaker966or second bypass breaker994. Additionally, since the removal of both copies of the fifth key (K6) causes switching logic950of first static transfer switch906to be disabled and switching logic982of second transfer switch981to be disabled, this provides a further safeguard for ensuring that first load bus910is not being powered by a different power source than second load bus914when second bus tie breaker944is closed.

A second method for performing a closed-transition procedure in accordance with the key interlock system described above in reference toFIG. 9will now be described in reference to flowchart1400ofFIG. 14.

At step1402, the operator opens first source input breaker952of first static transfer switch906.

At step1404, the operator uses the first key (2K1) to transition second key interlock device966from its first state to its second state. At this point, second key interlock device966no longer impedes the closing of second bypass breaker962of first static transfer switch906and also allows removal of a copy of the fourth key (2K4).

At step1406, the operator closes second bypass breaker962. As noted above, in an embodiment, this causes a pilot light associated with solenoid key release unit976to be turned on. The turning on of the pilot light serves as a confirmation to the operator that second bypass breaker962is closed and also indicates to the operator that a copy of the sixth key (K7) can be removed from solenoid key release unit976by pressing a push button.

At step1408, the operator presses the push button associated with solenoid key release unit976which causes the copy of the sixth key (K7) to be released by solenoid key release unit976.

At step1410, the operator opens first source input breaker984of second static transfer switch981.

At step1412, the operator uses the second key (2K2) to transition fourth key interlock device997from its first state to its second state. At this point, fourth key interlock device997no longer impedes the closing of second bypass breaker994of second static transfer switch981and also allows removal of a copy of the fourth key (2K4).

At step1414, the operator closes second bypass breaker994. As noted above, in an embodiment, this causes a pilot light associated with solenoid key release unit999to be turned on. The turning on of the pilot light serves as a confirmation to the operator that second bypass breaker994is closed and also indicates to the operator that a copy of the sixth key (K7) can be removed from solenoid key release unit999by pressing a push button.

At step1416, the operator presses the push button associated with solenoid key release unit999which causes the copy of the sixth key (K7) to be released by solenoid key release unit999.

At step1418, the operator uses the two copies of the fourth key (2K4) and the two copies of the sixth key (K7) to transition key transfer block980to a state in which a copy of the seventh key (2K5) can be removed therefrom.

At step1420, the operator then takes the copy of the seventh key (2K5) that was released from key transfer block980and uses it to transition seventh key interlock device972from its first state to its second state. At this point, seventh key interlock device972is not impeding the closing of second bus tie breaker944.

At step1422, the operator then closes second bus tie breaker944, thereby electrically connecting first load bus910to second load bus914while they are both being powered by first power source904. After this point, either first static transfer switch906can be disconnected from first load bus910(e.g., by transitioning fifth key interlock device968from its second state to its first state and then opening main breaker922) or second static transfer switch981can be disconnected from second load bus914(e.g., by transitioning sixth key interlock device970from its second state to its first state and then opening main breaker934) without any discontinuity of power to the loads connected to first load bus910or second load bus914.

In accordance with the foregoing key interlock system and method, since key transfer block980will not release the copy of the seventh key (2K5) required to close second bus tie breaker444without first receiving both copies of the sixth key (K7), and since both copies of the sixth key (K7) will not be released by solenoid key release units976,999until both second bypass breaker962and second bypass breaker994are closed, this key interlock system and method ensures that both second bypass breaker962and second bypass breaker994have been closed before the operator is permitted to close second bus tie breaker944. Furthermore, since key transfer block980also captures both copies of the fourth key (2K4), this key interlock system and method ensures that the operator cannot close second bus tie breaker944and then use the copies of the fourth key (2K4) to go back and open second bypass breaker962or second bypass breaker994and possibly close first bypass breaker960or first bypass breaker992. Additionally, since the removal of both copies of the sixth key (K7) causes switching logic950of first static transfer switch906to be disabled and switching logic982of second transfer switch981to be disabled, this provides a further safeguard for ensuring that first load bus910is not being powered by a different power source than second load bus914when second bus tie breaker944is closed.

FIG. 15depicts a flowchart1500of a generalized method for automatically disabling switching logic of a static transfer switch having at least one bypass breaker in accordance with an embodiment. The method of flowchart1500may be implemented, for example, by static transfer switch406of electric power distribution system400or by one or more of first static transfer switch906and second static transfer switch981of electric power distribution system900.

As shown inFIG. 15, the method of flowchart1500begins at step1502in which it is automatically detected that a first bypass breaker of the static transfer switch has been closed. For example, with respect to static transfer switch406, this step may comprise detecting that first bypass breaker460has been closed. With respect to first static transfer switch906, this step may comprise detecting that first bypass breaker960has been closed. With respect to second static transfer switch981, this step may comprise detecting that first bypass breaker992has been closed.

At step1504, in response to at least detecting that the first bypass breaker of the static transfer switch has been closed, a first key is enabled to be removed from a first solenoid key release unit. For example, with respect to static transfer switch406, this step may comprise enabling the third key (K6) to be removed from solenoid key release unit474in response to at least detecting that first bypass breaker460has been closed. With respect to first static transfer switch906, this step may comprise enabling the copy of the fifth key (K6) to be removed from solenoid key release unit974in response to at least detecting that first bypass breaker960has been closed. With respect to second static transfer switch981, this step may comprise enabling the copy of the fifth key (K6) to be removed from solenoid key release unit998in response to at least detecting that first bypass breaker992has been closed.

At step1506, it is automatically detected that a first key has been removed from the first solenoid key release unit. For example, with respect to static transfer switch406, this step may comprise automatically detecting that the third key (K6) has been removed from solenoid key release unit474. With respect to first static transfer switch906, this step may comprise automatically detecting that the copy of the fifth key (K6) has been removed from solenoid key release unit974. With respect to second static transfer switch981, this step may comprise automatically detecting that the copy of the fifth key (K6) has been removed from solenoid key release unit998.

At step1510, in response to at least detecting that the first key has been removed from the first solenoid key release unit, the switching logic of the static transfer switch is disabled. For example, with respect to static transfer switch406, this step may comprise disabling switching logic450of static transfer switch406in response to detecting that the third key (K6) has been removed from solenoid key release unit474. With respect to first static transfer switch906, this step may comprise disabling switching logic950of first static transfer switch906in response to detecting that the copy of the fifth key (K6) has been removed from solenoid key release unit974. With respect to second static transfer switch981, this step may comprise disabling switching logic982of second static transfer switch981in response to detecting that the copy of the fifth key (K6) has been removed from solenoid key release unit998.

FIG. 16depicts a flowchart1600of a generalized method for automatically disabling switching logic of a static transfer switch having two bypass breakers in accordance with an embodiment. The method of flowchart1600may be implemented, for example, by one or more of first static transfer switch906and second static transfer switch981of electric power distribution system900.

As shown inFIG. 16, the method of flowchart1600begins at step1602in which it is automatically detected that a second bypass breaker of the static transfer switch has been closed. For example, with respect to first static transfer switch906, this step may comprise detecting that second bypass breaker962has been closed. With respect to second static transfer switch981, this step may comprise detecting that second bypass breaker994has been closed.

At step1604, in response to at least detecting that the second bypass breaker of the static transfer switch has been closed, a second key is enabled to be removed from a second solenoid key release unit. For example, with respect to first static transfer switch906, this step may comprise enabling the copy of the sixth key (K7) to be removed from solenoid key release unit976in response to at least detecting that second bypass breaker962has been closed. With respect to second static transfer switch981, this step may comprise enabling the copy of the sixth key (K7) to be removed from solenoid key release unit999in response to at least detecting that second bypass breaker994has been closed.

At step1606, it is automatically detected that a second key has been removed from the second solenoid key release unit. For example, with respect to first static transfer switch906, this step may comprise automatically detecting that the copy of the sixth key (K7) has been removed from solenoid key release unit976. With respect to second static transfer switch981, this step may comprise automatically detecting that the copy of the sixth key (K7) has been removed from solenoid key release unit999.

At step1610, in response to at least detecting that the second key has been removed from the second solenoid key release unit, the switching logic of the static transfer switch is disabled. For example, with respect to first static transfer switch906, this step may comprise disabling switching logic950of first static transfer switch906in response to detecting that the copy of the sixth key (K7) has been removed from solenoid key release unit976. With respect to second static transfer switch981, this step may comprise disabling switching logic982of second static transfer switch981in response to detecting that the copy of the sixth key (K7) has been removed from solenoid key release unit999.

A key interlock system is described herein that includes a static transfer switch. The static transfer switch includes switching logic, a first bypass breaker, a first key interlock device, and a first solenoid key release unit. The switching logic is operable to selectively deliver power from one of a first power source or a second power source to a first load bus. The first bypass breaker is operable to be placed in either a closed state in which power can be delivered from the first power source to the first load bus via a path there between that bypasses the switching logic or in an open state in which power cannot be delivered from the first power source to the first load bus via the path there between that bypasses the switching logic. The first key interlock device is operable to be transitioned from a first state to a second state using a first key, the first state of the first key interlock device comprising a state in which the first key interlock device impedes closing of the first bypass breaker and prevents removal of a second key from the first key interlock device and the second state of the first key interlock device comprising a state in which the first key interlock device does not impede the closing of the first bypass breaker and enables removal of the second key from the first key interlock device. The first solenoid key release unit is operable to be placed in a non-energized state when the first bypass breaker is in the open state and to be placed in an energized state when at least the first bypass breaker is in the closed state. The first solenoid key release unit is further operable to prevent removal of a third key therefrom when in the non-energized state and to enable removal of the third key therefrom when in the energized state. The second key and the third key are required to obtain a fourth key that is useable to transition a bus tie breaker that is connected between the first load bus and a second load bus from an open state to a closed state.

In one embodiment of the foregoing key interlock system, the first solenoid key release unit is operable to be placed in the energized state when the first bypass breaker is in the closed state and a push button is pressed.

In another embodiment, the foregoing key interlock system further includes an auxiliary contact that is connected between a third power source and the first solenoid key release unit, the auxiliary contact being linked to the first bypass breaker and being operable to deliver power from the third power source to the first solenoid key release unit when at least the first bypass breaker is placed in the closed state. The third power source may comprise an uninterruptible power source. The auxiliary contact may be further connected between the third power source and a pilot light, the auxiliary contact being operable to deliver power from the third power source to the pilot light when the first bypass breaker is placed in the closed state.

In yet another embodiment of the foregoing key interlock system, the first key interlock device comprises a first lock cylinder and a second lock cylinder. The first lock cylinder is configured to receive the first key and is rotatable thereby to transition the first key interlock device from the first state to the second state. The second lock cylinder is configured to receive the second key and is rotatable thereby to transition the first key interlock device from the second state to the first state. The first state of the first key interlock device further comprises a state in which the first key interlock device enables removal of the first key from the first key interlock device and the second state of the first key interlock device further comprises a state in which the first key interlock device prevents removal of the first key from the first key interlock device.

In further accordance with this embodiment, the static transfer switch further comprises a second bypass breaker and a second key interlock device. The second bypass breaker is operable to be placed in either a closed state in which power can be delivered from the second power source to the first load bus via a path there between that bypasses the switching logic or an open state in which power cannot be delivered from the second power source to the first load bus via the path there between that bypasses the switching logic. The second key interlock device comprises a lock cylinder that is configured to receive the first key and is rotatable thereby to transition the second key interlock device between a first state and a second state, the first state of the second key interlock device comprising a state in which the second key interlock device impedes closing of the second bypass breaker and in which the second key interlock device enables removal of the first key from the second key interlock device and the second state of the second key interlock device comprising a state in which the second key interlock device does not impede the closing of the second bypass breaker and in which the second key interlock device prevents removal of the first key from the second key interlock device.

In still another embodiment, the foregoing key interlock system further includes a key transfer block that is operable to be transitioned from a first state to a second state using both the second key and the third key, the first state of the key transfer block comprising a state in which the key transfer block prevents removal of the fourth key from the key transfer block and the second state of the key transfer block comprising a state in which the key transfer block enables removal of fourth key from the key transfer block.

In a further embodiment of the foregoing key interlock system, the bus tie breaker comprises one of two bus tie breakers that are connected in series between the first load bus and the second load bus.

In a still further embodiment of the foregoing key interlock system, the static transfer switch is operable to disable the switching logic from delivering power to the first load bus from either the first power source or the second power source in response to detecting that the third key has been removed from the first solenoid key release unit.

Another key interlock system is described herein that includes a first static transfer switch, a second static transfer switch, a first key transfer block and a second key transfer block.

The first static transfer switch comprises first switching logic, a first bypass breaker, a first solenoid key release unit, a second bypass breaker, and a second solenoid key release unit. The first switching logic is operable to selectively deliver power from either a first power source or a second power source to a first load bus. The first bypass breaker, when closed, enables power to be delivered from the first power source to the first load bus via a first bypass path that bypasses the first switching logic. The first solenoid key release unit releases a first key when at least the first bypass breaker is closed. The second bypass breaker, when closed, enables power to be delivered from the second power source to the first load bus via a second bypass path that bypasses the first switching logic.

The second solenoid key release unit releases a second key when at least the second bypass breaker is closed. The second static transfer switch comprises second switching logic, a third bypass breaker, a third solenoid key release unit, a fourth bypass breaker, and a fourth solenoid key release unit. The second switching logic is operable to selectively deliver power from either the first power source or the second power source to a second load bus. The third bypass breaker, when closed, enables power to be delivered from the first power source to the second load bus via a third bypass path that bypasses the second switching logic. The third solenoid key release unit releases a third key when at least the third bypass breaker is closed. The fourth bypass breaker, when closed, enables power to be delivered from the second power source to the second load bus via a fourth bypass path that bypasses the second switching logic. The fourth solenoid key release unit releases a fourth key when at least the fourth bypass breaker is closed.

The first key transfer block is operable to release a fifth key that is useable to close a bus tie breaker that is connected between the first load bus and the second load bus in response to at least insertion of the first key and the third key.

The second key transfer block is operable to release a sixth key that is useable to close the bus tie breaker that is connected between the first load bus and the second load bus in response to at least insertion of the second key and the fourth key.

In one embodiment of the foregoing key interlock system, the first transfer switch further comprises a first key interlock device and a second key interlock device. The first key interlock device, when activated with a seventh key, enables the first bypass breaker to be closed and releases an eighth key. The second key interlock device, when activated with the seventh key, enables the second bypass breaker to be closed and releases a ninth key. In further accordance with this embodiment, the second transfer switch further comprises a third key interlock device and a fourth key interlock device. The third key interlock device, when activated with a tenth key, enables the third bypass breaker to be closed and releases an eleventh key. The fourth key interlock device, when activated with the tenth key, enables the fourth bypass breaker to be closed and releases a twelfth key. In still further accordance with this embodiment, the first transfer block is operable to release the fifth key in response to at least insertion of the first key, the third key, the eighth key and the eleventh key and the second transfer block is operable to release the sixth key in response to at least insertion of the second key, the fourth key, the ninth key and the twelfth key.

In another embodiment of the foregoing key interlock system, the first solenoid key release unit releases the first key when the first bypass breaker is closed and a first push button is pressed, the second solenoid key release unit releases the second key when the second bypass breaker is closed and a second push button is pressed, the third solenoid key release unit releases the third key when the third bypass breaker is closed and a third push button is pressed, and the fourth solenoid key release unit releases the fourth key when the fourth bypass breaker is closed and a fourth push button is pressed.

In further accordance with this embodiment, the first static switch comprises a first pilot light that is lit when the first bypass breaker is closed and a second pilot light that is lit when the second bypass breaker is closed, and the second static switch comprises a third pilot light that is lit when the third bypass breaker is closed and a fourth pilot light that is lit when the fourth bypass breaker is closed.

In yet another embodiment of the foregoing key interlock system, each of the first solenoid key release unit, the second solenoid key release unit, the third solenoid key release unit, and the fourth solenoid key release unit is powered by a power source other than the first power source or the second power source.

In still another embodiment of the foregoing key interlock system, at least one of the first solenoid key release unit, the second solenoid key release unit, the third solenoid key release unit, and the fourth solenoid key release unit is powered by an uninterruptible power source.

In a further embodiment of the foregoing key interlock system, the bus tie breaker comprises one of two bus tie breakers that are connected between the first load bus and the second load bus.

In a still further embodiment of the foregoing key interlock system, the first static transfer switch is operable to disable the first switching logic from delivering power to the first load bus from either the first power source or the second power source in response to determining that the first key has been removed from the first solenoid key release unit or that the second key has been removed from the second solenoid key release unit, and the second static transfer switch is operable to disable the second switching logic from delivering power to the second load bus from either the first power source or the second power source in response to determining that the third key has been removed from the third solenoid key release unit or that the fourth key has been removed from the fourth solenoid key release unit.

A method for implementing a static transfer switch that includes switching logic that is operable to selectively deliver power from either a first power source or a second power source to a load bus is described herein. The method includes: detecting that a first bypass breaker of the static transfer switch has been closed, the closing of the first bypass breaker enabling power to be delivered from the first power source to the load bus via a path there between that bypasses the switching logic; in response to at least detecting that the first bypass breaker has been closed, enabling a first key to be removed from a first solenoid key release unit; detecting that the first key has been removed from the first solenoid key release unit; and in response to at least detecting that the first key has been removed from the first solenoid key release unit, disabling the switching logic from delivering power to the load bus from either the first power source or the second power source.

The foregoing method may further include detecting that a second bypass breaker of the static transfer switch has been closed, the closing of the second bypass breaker enabling power to be delivered from the second power source to the load bus via a path there between that bypasses the switching logic; in response to at least detecting that the second bypass breaker has been closed, enabling a second key to be removed from a second solenoid key release unit; detecting that the second key has been removed from the second solenoid key release unit; and in response to at least detecting that the second key has been removed from the second solenoid key release unit, disabling the switching logic from delivering power to the load bus from either the first power source or the second power source.