Patent Publication Number: US-7898372-B2

Title: Method and apparatus for control contacts of an automatic transfer switch

Description:
RELATED APPLICATIONS 
     This application claims priority to provisional application No. 60/771,047, filed Feb. 6, 2006. 
    
    
     BACKGROUND 
     1. Field of the Application 
     This application relates generally to electrical power transfer switches. More specifically, the present application relates to automatic transfer switches. 
     2. Description of Related Art 
     In general, a typically available automatic transfer switch consists of a number of components. For example, such transfer switches generally comprise a main switch panel with power contacts, a solenoid actuator, a set of solenoid control contacts, and a set of auxiliary contacts. The solenoid actuator typically is used to close and open the power contacts through a mechanical switching mechanism. The auxiliary contacts are used for position sensing which information is used by an electronic controller. The solenoid control contacts control the amount of time that the solenoid is energized. In addition, the auxiliary contacts provide additional functions for the customer. 
     A power transfer from a “normal” power source to an alternate “emergency” power source is initiated by the electronic controller energizing the solenoid actuator. The solenoid actuator is energized until the switching mechanism is moved to a desired position and the coil control contacts cut off power to the solenoid actuator. 
     In a typical switch construction, such as the switch construction illustrated in  FIG. 1 , the auxiliary contacts  10  and the solenoid control contacts  12  are actuated by a moving mechanical linkage  12 . Another example of a typical switch construction is illustrated in  FIGS. 2-4 . In the switch construction illustrated in  FIGS. 2-4 , the solenoid control contacts  20  are mounted on top of a rotating weight  28  (shown in  FIG. 3 ). The auxiliary contacts  22  are connected to the rotating weight with a link  24 . In other methods such as the methods described in U.S. Pat. No. 6,849,811, auxiliary contacts and solenoid control contacts are located apart from the switching mechanism and are attached to moving components of the power contacts. U.S. Pat. No. 6,849,811 is herein entirely incorporated by reference and to which the reader is directed to for further information. 
     In yet another method, as is described in U.S. Pat. No. 6,815,622, the auxiliary contacts are attached to components of the power contacts. In addition, the solenoid control contacts are connected by a link to the switching mechanism. U.S. Pat. No. 6,815,622 is herein entirely incorporated by reference and to which the reader is directed to for further information. 
     Although the referenced designs are generally successful in providing functioning auxiliary and coil control contacts having certain advantages, their design features have certain limitations. For example, such known methods may not be fully optimized for parts reduction, efficient assembly, less costly maintenance, and/or improved reliability. As just one example, the design method illustrated in  FIG. 1  includes auxiliary contacts and solenoid control contacts coupled together and actuated by a single link having pin joints. During an actuation, the link is often exposed to either tensile or compressive forces. If the bearing friction in the pin joints or the actuation torque of the auxiliary and coil control contacts increases due to wear, contamination, or other situations, the link may bend. Such linkage bending may result in jamming the mechanism. One negative consequence of this situation is that it could affect the time that the solenoid actuator coil is energized and the apparent switch position sensed by the electronic controller through the auxiliary contacts. This may lead to possible coil overheating and switch failure. 
     The example shown in  FIGS. 2-4  has certain design advantages over the design illustrated in  FIG. 1 . For example, in the design illustrated in  FIGS. 2-4 , the solenoid control contacts  20  are mounted on top of the rotating weight  28 . However, in this method, the auxiliary contacts  22  are actuated by a link  24  as shown in  FIG. 4 . While the reliability of the coil control contacts is improved over the previously discussed design, the reliability of auxiliary contacts is still dependent on the quality of link connection with the auxiliary contacts  22 . 
     The design examples described in U.S. Pat. Nos. 6,815,622 and 6,849,811 both have the auxiliary contacts located apart from the switching mechanism and connected to the moving components power contacts. Since the auxiliary contacts are on the “other side” of the switch panel, the motion from the solenoid actuator must be translated through a series of components. In this case, the reliability depends upon the quality of each individual component. In addition, the larger the number of components required to actuate either the solenoid control or auxiliary contacts, the greater the probability of incorrect assembly, misalignments, loose parts, excessive wear, inadequate lubrication, or other similar mechanical type problem, which are all possible contributors to solenoid actuator overheating and automatic transfer failure. 
     SUMMARY 
     In one preferred arrangement, an automatic transfer switch is provided that includes a solenoid control contacts assembly, an auxiliary contacts assembly, a multi or dual purpose cam attached to a cylindrical shaped weight, and a solenoid actuator. When energized, the solenoid actuator rotates the cylindrical weight and the dual purpose cam actuates both the solenoid control contacts assembly and the auxiliary contacts assembly. 
     The method of actuating the contacts has a number of design advantages. For example, one advantage is that both the auxiliary contacts and the solenoid control contacts are located next to the solenoid actuator. One advantage of this arrangement is that there is no need for additional linkages. Another advantage of this arrangement is that both the auxiliary contacts assembly and the solenoid control contacts assembly are actuated by the same dual purpose cam. A further advantage of the method of the present application is that it provides for better control of the timing between solenoid actuator voltage cutoff and closing or opening of the auxiliary contacts. 
     This method can be utilized to design automatic transfer switches with fewer parts, easier assembly, simpler maintenance, and improved reliability. 
     In another arrangement, effectively providing an identical function, the dual purpose cam may be a modular design with all modules attached to the rotating weight. In this arrangement, both the auxiliary contacts and the solenoid control contacts are again located next to the solenoid actuator. Therefore, in this alternative arrangement, there is no need for additional linkages. A further advantage of this arrangement is that it provides improved control of the timing between solenoid actuator voltage cutoff and closing or opening of the auxiliary contacts. 
     These as well as other aspects and advantages will become apparent to those of ordinary skill in the art by reading the following detailed description, with reference where appropriate to the accompanying drawings. Further, it should be understood that the embodiments described in this summary and elsewhere are intended to illustrate the invention by way of example only. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary arrangements of the invention are described herein with reference to the drawings, in which: 
         FIG. 1  illustrates a prior art design method in which auxiliary contacts and the solenoid control contacts are actuated by a linkage; 
         FIG. 2  illustrates a prior art design method in which the solenoid control contacts are mounted on top of the rotating weight and the auxiliary contacts are mounted separately on the switching mechanism frame and attached to the rotating weight with a linkage; 
         FIG. 3  is a side view of the prior art design method illustrated in  FIG. 2 ; 
         FIG. 4  shows a detailed view of the auxiliary contacts and the actuation link illustrated in  FIGS. 2 and 3 ; 
         FIG. 5  illustrates solenoid control and auxiliary contacts located above a rotating weight; 
         FIG. 6  illustrates a dual purpose cam used to actuate the solenoid control and auxiliary contacts illustrated in  FIG. 5 ; 
         FIG. 7  illustrates the auxiliary contacts assembly and the solenoid control contacts assembly and the solenoid control miniature switches and push-buttons; 
         FIG. 8  is a side view of the solenoid control and auxiliary contacts located above a rotating weight illustrated in  FIG. 5 ; 
         FIG. 9  illustrates the orientation of components in a normal position; 
         FIG. 10  illustrates the orientation of components in an emergency position; 
         FIG. 11  illustrates the auxiliary contacts assembly in detail; 
         FIG. 12  illustrates the dual purpose cam in detail; and 
         FIG. 13  illustrates an example of a modular dual purpose cam. 
     
    
    
     DETAILED DECSRIPTION 
     Referring to  FIG. 5 , a transfer switch  100  is illustrated according to a preferred arrangement. The transfer switch  100  comprises an auxiliary contacts assembly  102  and solenoid control contacts assembly  104 . Both the auxiliary contacts assembly  102  and solenoid control contacts assembly  104  are located adjacent a solenoid actuator  106 . Preferably, the contact assemblies  102  and  104  are actuated by a dual purpose actuation cam  110  (illustrated in  FIG. 6 ). 
     Referring now to  FIG. 6 , the actuation cam  110  is attached to a rotating weight  112 . Although the rotating weight  112  is illustrated as a weight  112  having a cylindrical shape, alternative shaped weights may also be used. A washer  114  and a screw  116  may be included to secure the actuation cam  110  to the rotating weight  112 . Alternatively, in a different arrangement, the actuation cam  110  may be secured to the rotating weight  112  by any other known fastening device. 
     In this preferred arrangement, the actuation cam  110  has both a first pair of actuating surfaces  118  and a second pair of actuating surfaces  120 . The first pair of actuating surfaces  118  is used to actuate the auxiliary contacts  102 . The second pair of actuating surfaces  120  is used to actuate the solenoid control contacts  104 . Alternative actuating surface configurations may also be used. 
     Referring to  FIGS. 7 and 8 , the auxiliary contacts assembly  102  is located above a narrow portion of the actuation cam  110 . The solenoid control contacts assembly  104  is located above the wide portion of the actuation cam  110 . Both auxiliary contacts assembly  102  and solenoid control contacts assembly  104  are attached to a common frame  118 . 
     As shown in  FIG. 9 , a solenoid link  120  is attached between the solenoid actuator  106  and the rotating weight  112 . When the solenoid actuator  106  is energized, its linear motion is converted into a rotational motion of the rotating weight  112  through the solenoid link  120 . The rotating weight  112  and the actuation cam  110  rotate together between two positions. The first position is the normal position. As referred to before, this normal position is illustrated in  FIG. 9 . In the normal position, the actuation cam  110  is located on the left side of the rotating weight  112  and therefore displaces the left row of miniature switch levers  122  of the auxiliary contacts  102 . 
     The second position, or the emergency position, is illustrated in  FIG. 10 . In the emergency position, the actuation cam  110  is located on the right side of the rotating weight  112 . In this location, the actuation cam  110  displaces the right row of miniature switch levers  124  of the auxiliary contacts  102 . 
       FIG. 11  illustrates a preferred arrangement of the auxiliary contacts assembly  102 . In this arrangement, auxiliary contacts assembly  102  comprises a frame  132 , a first set of switches  122 , a second set of switches  124 , an insulator  126 , a plurality of washers  130 , and a plurality of screws  128 . The first set of switches  122  and the second set of switches  124  are associated with the left “normal” switches and the right “emergency” switches, respectively. The plurality of screws  128  and washers  130  secure the first switches  122  and second switches  124  onto the frame  132  of the auxiliary contacts assembly  102 . Alternatively, the switches  122  and  124  may be secured to the frame  132  by any other known fastening device. 
     Preferably, the solenoid control contacts assembly  104  comprises at least two miniature switches  134  and  136 , as shown in  FIG. 7 . The first miniature switch  134  is used to control the transfer from the normal position to the emergency position. The second miniature switch  136  is used to control the transfer from the emergency position to the normal position. In the normal position, the first miniature switch  134  is closed and the second miniature switch  136  is open. In the emergency position, the first miniature switch  134  is open and the second miniature switch  136  is closed. 
     During a power transfer from the normal position to the emergency position, the solenoid actuator  106  is energized through the closed first miniature switch  134 . The solenoid actuator  106  remains energized until the first miniature switch  134  opens when its push-button  138  reaches an emergency cutoff surface  142 . The emergency cutoff surface  142  of the rotating weight  112  is illustrated in  FIG. 12 . 
     During a power transfer from the emergency position to the normal position, the solenoid actuator  106  is energized through the closed second miniature switch  136 . The solenoid actuator  106  remains energized until the second miniature switch  136  opens when its push-button  140  reaches a normal cutoff surface  144 . The normal cutoff surface  144  of the rotating weight  112  is illustrated in  FIG. 12 . 
     Referring to  FIG. 13 , an alternative arrangement of the transfer switch is illustrated. In this alternative arrangement, the transfer switch includes an auxiliary contacts module  102 ′, a solenoid control contacts module  104 ′, an actuation cam  110 ′, and a rotating weight  112 ′. The actuation cam  110 ′ is modular and is secured to the rotating weight  112 ′ by fasteners  146 . 
     While certain features and embodiments of the present application have been described in detail herein, it is to be understood that the application encompasses all modifications and enhancements within the scope and spirit of the following claims.