Abstract:
A power backfeed apparatus includes a housing configured be removably positioned in a compartment of a motor control center (MCC), a contact assembly supported by the housing and comprising at least one contact configured to face a corresponding at least one power conductor of the MCC when the housing is disposed in the compartment and a power cable connector supported by the housing and configured to support connection of an external power cable thereto when the housing is disposed in the compartment, the power cable connector configured to be electrically coupled to the at least one contact of the contact assembly. A contact engagement mechanism forces the at least one contact into contact with the at least one power conductor to electrically couple the at least one contact and the at least one power conductor.

Description:
FIELD 
       [0001]    The inventive subject matter relates generally to motor control centers and methods of operation thereof and, more particularly, to apparatus and methods for providing power to motor control centers. 
       BACKGROUND 
       [0002]    Motor control centers (MCCs) are assemblies designed to contain motor starters, variable frequency drives, programmable controllers, meters and other industrial electrical equipment. MCCs are commonly used in manufacturing facilities, power plants and other industrial locations. 
         [0003]    A typical MCC includes one or more cabinet-like enclosures, each including a plurality of compartments or “buckets” configured to receive motor controllers and/or other types of modules. MCCs typically include one or more power bus bars to which these modules are connected. For example, a module may include “stab” contacts that extend from a rear face of the module and that are configured to engage power bus bars located proximate a rear section of the bucket into which the module is placed. These contacts may be moveable and may be actuated to engage with and disengage from the power bus bars using a motor drive and/or a tool interface at a front face of the module. MCC and module configurations are described, for example, in U.S. Pat. No, 8,054,606 to Morris et al. and U.S. Patent Application Publication No. 2011/0149480 to Leeman et al. 
         [0004]    Within a given MCC, certain loads may be more critical than others. For example, in a nuclear power plant, motor controllers that control motor operated valves (MOVs) that control flow of cooling water to the reactors may be more critical than other loads. Under emergency conditions, it is generally desirable to keep these critical loads on line. Accordingly, nuclear power plants typically have redundant power systems that are configured to power critical loads from a secondary power source, such as a permanently-installed backup diesel engine-generator set. Unfortunately, however, these secondary power systems may also fail, as was the case, for example, in the Fukushima Daiichi nuclear disaster of 2011. 
       SUMMARY 
       [0005]    Some embodiments of the inventive subject matter provide a power backfeed apparatus including a housing configured be removably positioned in a compartment of a motor control center (MCC) and a contact assembly supported by the housing and comprising at least one contact configured to face a corresponding at least one power conductor of the MCC when the housing is disposed in the compartment. The apparatus also includes a power cable connector supported by the housing and configured to support connection of an external power cable thereto, with the power cable connector being configured to be electrically coupled to the at least one contact of the contact assembly. The apparatus further includes a contact engagement mechanism configured to force the at least one contact into contact with the at least one power conductor to electrically couple the at least one contact and the at least one power conductor and thereby support provision of power from the power cable connector to the at least one power conductor of the MCC. 
         [0006]    In some embodiments, the at least one contact may be fixed in relation to the housing and the contact engagement mechanism may be configured to force the housing toward the at least power conductor to cause the at least one contact to engage the at least one power conductor. The contact engagement mechanism may include a surface configured to contact a door of the compartment such that closing the door forces the housing toward the at least one power conductor to engage the at least one contact with the at least one power conductor of the MCC. The contact engagement mechanism may include a member, such as a spring-loaded plunger, extending from a face of the housing and having a surface configured to engage the door of the compartment. In some embodiments, the contact assembly may include a plurality of elongate members extending from a face of the housing and the at least one contact may include a plurality contacts, respective ones mounted at ends of respective ones of the elongate members. 
         [0007]    In further embodiments, the contact assembly may include a moveable contact assembly. The contact engagement mechanism may include an actuator configured to move the moveable contact assembly to cause motion of the at least one contact relative to the housing. The actuator may be manual and/or motorized, and may be remotely operable using, for example, a wired or wireless control link or manual cable. 
         [0008]    The contact assembly may include a moveable body comprising a plurality elongate members and the at least one contact may include a plurality contacts, respective ones mounted proximate ends of respective ones of the elongate members. The contact engagement mechanism may be configured to move the body and cause the elongate members to retractably extend through a face of the housing. 
         [0009]    In some embodiments, the apparatus may further include a disconnect device supported by the housing and configured to couple and decouple the at least one contact and the power cable connector. The disconnect device may include a manual actuator accessible at a front face of the housing. The disconnect device may be remotely operable. 
         [0010]    Further embodiments of the inventive subject matter provide a power backfeed apparatus including a housing configured be removably positioned in a compartment of an MCC and a contact assembly comprising at least one member mounted at a rear face of the housing and at least one contact supported by the at least one member and facing towards at least one power conductor of the MCC when the housing is disposed in the compartment. The apparatus also includes a power cable connector supported by the housing and configured to support connection of an external power cable to the power cable connector. The power cable connector is configured to be electrically coupled to the at least one contact of the contact assembly. The apparatus further includes a member supported by the housing and configured to engage a door of the compartment such that closure of the door moves the housing and forces the at least one contact into contact with the at least one power conductor to electrically couple the at least one contact and the at least one power conductor and thereby support provision of power from the power cable connector to the at least one power conductor of the MCC. The member may include a spring-loaded plunger mounted at a face of the housing. 
         [0011]    Further embodiments provide methods of operating an MCC. The methods include positioning a backfeed module in a compartment of the MCC, connecting an external power cable to a power cable connector of the backfeed module and forcing at least one contact of the backfeed module into contact with at least one power conductor of the MCC in the compartment to electrically couple the at least one contact and the at least one power conductor and thereby support provision of power from the external power cable to the at least one power conductor of the MCC. In some embodiments, forcing at least one contact of the backfeed module into contact with at least one power conductor of the may include closing a door of the compartment such that contact of the door with a surface of the module moves the module and forces engagement of the at least one contact with the at least one power conductor. In further embodiments, forcing at least one contact of the backfeed module into contact with at least one power conductor of the may include actuating a moveable contact assembly of the backfeed module. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIGS. 1-3  are views illustrating a backfeed module for an MCC according to some embodiments of the inventive subject matter. 
           [0013]      FIG. 4  illustrates a typical installation of the backfeed module of  FIGS. 1-3  in a compartment of an MCC. 
           [0014]      FIG. 5  is a detailed view of a stab assembly of the backfeed module of  FIGS. 1-3  engaged with power bus bars of an MCC. 
           [0015]      FIG. 6  is a block diagram illustrating components of a backfeed module according to further embodiments of the inventive subject matter. 
           [0016]      FIGS. 7 and 8  illustrate operations for installing the backfeed module of  FIGS. 1-5  in an MCC according to further embodiments of the inventive subject matter. 
           [0017]      FIG. 9  is a perspective view of a back feed module with a manually actuated stab assembly according to some embodiments of the inventive subject matter. 
           [0018]      FIG. 10  is a perspective view of a back feed module with a remotely actuated stab assembly according to further embodiments. 
           [0019]      FIG. 11  is a perspective view of a back feed module with a cable-activated disconnect switch according to further embodiments. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    The inventive subject matter now will be described more fully hereinafter with reference to the accompanying drawings, in which illustrative embodiments of the inventive subject matter are shown. In the drawings, the relative sizes of regions or features may be exaggerated for clarity. This inventive subject matter may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive subject matter to those skilled in the art. 
         [0021]    It will be understood that when an element is referred to as being “coupled” or “connected” to another element, it can be directly coupled or connected to the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly coupled” or “directly connected” to another element, there are no intervening elements present. Like numbers refer to like elements throughout. As used herein the term “and/or” includes any and all combinations of one or more of the associated listed items. 
         [0022]    In addition, spatially relative terms, such as “under”, “below”, “lower”, “over”, “upper” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “under” or “beneath” other elements or features would then be oriented “over” the other elements or features. Thus, the exemplary term “under” can encompass both an orientation of over and under. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. 
         [0023]    The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the inventive subject matter. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein the expression “and/or” includes any and all combinations of one or more of the associated listed items. 
         [0024]    Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this inventive subject matter belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
         [0025]    Some embodiments of the inventive subject matter arise from a realization that power may be provided to an MCC in emergency situations using a backfeed module configured to be inserted into an MCC compartment and to provide power to the power conductors (e.g., bus bars) of the MCC from an external power source, such as a portable generator, connected to the module via a power cable connector. In some embodiments, the module may be designed to engage the power bus bars of the MCC using contacts that are configured to be forced against the bus(es) by closing a compartment door. In further embodiments, a manually and/or electrically driven actuator may force contacts of the module to engage with the MCC power bus bars, thus allowing an operator to connect the module to the bus at a safe distance. The module may include a circuit interruption device, such as circuit breaker. 
         [0026]      FIGS. 1-3  illustrate a backfeed module  100  for an MCC according to some embodiments. The module  100  includes a housing  110  configured to be inserted in a compartment or bucket of an MCC. Spring-loaded plunger assemblies  130  are mounted at a front face  114  of the housing. A power cable connector  150  is mounted at a side face  116  of the housing. It will be appreciated that the power cable connector  150  may be mounted at a different face of the housing  110 , such as the front face  114 , depending on access requirements. A handle  140  may be attached to the housing  110  to ease carrying of the module  100 . 
         [0027]    Referring to  FIGS. 2-5 , a stab contact assembly  120  is mounted at a rear face  112  of the housing  110 . The stab contact assembly  120  includes a plurality of elongate members  122  which extend away from the rear face  112 . Stab contacts  124  are mounted proximate ends of the members  122 . As shown in  FIGS. 4 and 5 , the module  110  is configured such that, when the module  110  is inserted into a compartment  410  of an MCC, the module  110  rests on a supporting surface  440  (e.g., a shelf) and may slide toward a power bus bars  430  of the MCC. Referring to  FIG. 5 , the stab assembly  120  is configured such that respective ones of the stab contacts  124  engage respective ones of the bus bars  430 . As shown in  FIG. 4 , this engagement may be effected by applying force to the spring-loaded plunger assemblies  130  mounted at the front face  114  of the module  110 . 
         [0028]    The contacts  124  of the contact assembly  120  are configured to be electrically coupled to the power cable connector  150  to support provision of power to the bus bars  430  from a power source coupled to the power cable connector  150 . The connection between the power cable connector  150  and the contacts  124  may be direct (e.g., via wires or other conductors) or, as further shown in  FIGS. 1-3 , the module  100  may further include a disconnect device, here shown as a switch  160 , configured to couple and decouple the contacts  124  to and from the power cable connector  150 . As shown, the switch  160  may be manually actuated using a handle accessible at the front face  114  of the housing  110 . In some embodiments, the disconnect device may be remotely actuated using, for example, a motor drive, cable or similar mechanism. The disconnect device  160  may simply function as a switch or may be a circuit breaker or similar device that provides automatic circuit interruption capabilities. 
         [0029]      FIGS. 6 and 7  illustrate installation of the backfeed module  100  in a compartment  410  of an MCC  400 . Power bus bars  430  are positioned in a rear section of the compartment  410 . When a door  420  of the compartment is closed, the door  420  contacts the spring-loaded plungers  130  extending from the backfeed module  100 , forcing the module  110  rearward to engage the bus bars  430  as shown in  FIG. 5 . The door  420  may be fixed in place by panel screws or other retaining means, causing the stab contacts  124  of the module to be maintained in contact with the bus bars  430  in a spring loaded fashion. A power cable may be routed through internal spaces of the MCC  440  to connect to the power cable connector  150  of the module  110  and/or access to the power cable connector  150  may be provide via a cutout in the door  420 . Cutouts in the door  420  may also provide access to the disconnect switch  160 . 
         [0030]      FIG. 8  is a schematic block diagram illustrating electrical connections of the module  100  within the MCC  400  according to some embodiments. An external generator  10 , for example, a portable engine/generator set, is coupled to an input of the disconnect device  160  via the power cable connector  150 . An output of the disconnect device  160  is coupled to the stab contact assembly  120 , which engages one or more bus bars  430  of the MCC  400 . It will be appreciated that the connections may be single or multi-phase. It will also be appreciated that the module  100  may include other electrical and/or electronic components, such as current and/or voltage sensors. The module  100  may also include r communications circuitry (wireline or wireless) for communicating information from such sensors and/or other status information. Such other status information may relate, for example, to the state of connection of the module to the bus bars  430 , the state of the external power source coupled to the power cable connector  150  and/or the state of the disconnect device  160 . The module  150  may also include display components that provide local indication of such information at the module  100  using, for example, displays or other indicators mounted at the front face  114  of the module  100 . 
         [0031]    In further embodiments, a backfeed module may use moveable contact assemblies similar to those used in other MCC modules. For example,  FIG. 9  illustrates a backfeed module  900  configured to be installed in a compartment  410  of an MCC, behind a door  420 . The backfeed module  900  includes a manually actuated retractable stab contact assembly  920  comprising a plurality of members  920  which may be moved towards a rear of the module  900  using a wrench-like tool inserted in a tool interface  970  via a cutout in the door  420 . Cutouts in the door  420  may also provide access to a power cable connector  950  and a disconnect switch  960  of the module  900 . The module  900  may include, for example, a screw-type actuator which, when rotated by the inserted tool, drives the stab contact assembly  920  towards bus bars of the MCC inside the compartment  410 , such that contacts  924  engage the bus bars. The moveable contact assembly  920  and the mechanism that drives it may be similar to, for example, mechanisms described in U.S. Pat. No. 8,199,022 to Morris et al., the disclosure of which is incorporated herein by reference in its entirety. 
         [0032]    In still further embodiments, a remotely operated contact drive assembly may be used to allow an operator to remotely actuate bus bar contacts of a backfeed module to increase installation safety.  FIG. 10  illustrates an example of such a backfeed module  1000  configured to be installed in a compartment  410  of an MCC, behind a door  420 . The backfeed module  1000  includes a moveable stab contact assembly  920  comprising a plurality of members  920 , which may be driven towards a rear of the module  1000  by a remotely-controlled driver mechanism  980 . The driver mechanism  980  may include, for example, a rotary motor configured to drive a screw mechanism that moves the contact assembly  920  or a linear motor configured to directly drive the contact assembly  920 . The motor may be electrically powered via the power cable connector  950  and may be controlled, for example, via a wired or wireless control link. The moveable contact assembly  920  and the mechanism that drives it may be similar, for example, to the movable contact mechanisms described in U.S. Pat. No. 8,054,606 to Morris et al., the disclosure of which is incorporated herein by reference in its entirety. In some embodiments, the driver mechanism  980  may be manually actuated using, for example, a rotary cable that drives a drive screw shaft that moves the stab contact assembly  920 . 
         [0033]    In additional embodiments, a backfeed module as described above may also include an actuator configured to provide remote operation of a disconnect device of the module. Such an actuator may include, for example, an electrical motor drive or a cable-driven mechanism (e.g., a Bowden push-pull type cable or rotary cable mechanism). For example,  FIG. 11  illustrates a backfeed module  100 ′ including a housing  110 , power cable connector  150 , spring-loaded plunger assemblies  130  and disconnect device  160  mounted at a front face  114  of the housing. The module  100 ′ further comprises a push-pull cable actuator assembly  170 , which is configured to allow a user to actuate the disconnect device  160  from a location removed from the module  100 ′. It will be appreciated that other embodiments may use different remote actuator mechanisms, such as motor-driven actuators controlled by wired and/or wireless control links. 
         [0034]    In the drawings and specification, there have been disclosed exemplary embodiments of the inventive subject matter. However, many variations and modifications can be made to these embodiments without substantially departing from the principles of the present inventive subject matter. Accordingly, although specific terms are used, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the inventive subject matter being defined by the following claims.