Patent Publication Number: US-2015084553-A1

Title: Synchronous transfer control system in an arc resistant enclosure

Description:
BACKGROUND 
     1. Field 
     The disclosed concept relates generally to a system for controlling the operation of multiple electric motors in an industrial setting (e.g., a pumping station), and, in particular, to a synchronous transfer control system that is provided in an arc resistant enclosure that meets IEEE C37.20,7 standards, 
     2. Background Information 
     There are numerous settings wherein multiple motors are employed to drive heavy machinery. For example, multiple high horsepower electric motors are used in a pumping system, such as, without limitation, a water pumping system. As is known in the art, in such settings, there are a number of devices that can be used to control the motors. In particular, contactors, soft starters, and variable frequency drives (VFDs) (also referred to as adjustable frequency drives or AFDs) are different types of devices that can be used to control a motor in such a setting. 
     A contactor simply connects the motor directly across the AC line. A motor connected to the AC line will accelerate very quickly to full speed and draw a large amount of current during acceleration. Thus, use of a contactor only to control a motor has many drawbacks, and in many industrial settings will not be permitted by the electric utility. A soft starter is a device used to slowly ramp up a motor to full speed, and/or slowly ramp down the motor to a stop. Reducing both current draw and the mechanical strain on the system are big advantages of using a soft starter in place of a contactor. Many large pumps and fans require at least a 30-second ramp time to prevent mechanical damage to the system. Soft starters are more common on larger horsepower systems. A VFD not only has the ramping ability of a soft starter, but also allows the speed to be varied, while offering more flexibility and features. 
     In addition, in settings where multiple motors are employed, there is the danger that one or more of the motors and/or motor drive devices could experience a fault resulting in a dangerous explosion. 
     There is thus a need for a system for controlling the operation of multiple electric motors in an industrial setting that wilt also protect workers in the environment in the event of dangerous fault condition. 
     SUMMARY 
     These needs and others are met by embodiments of the disclosed concept, which are directed to an arc resistant synchronous transfer control system for controlling operation of a number of electric motors. In one embodiment, the arc resistant synchronous transfer control system includes an arc resistant enclosure having a main housing having an open top portion and an arc plenum fluidly coupled to the top portion, the arc plenum having a closed front portion, a closed rear portion, and at least one open side portion structured for direct or indirect connection to a duct or vent system, the main housing having a number of enclosure members each made of a material having arc resistant ratings of 50 kA 0.5 s, Type 2B. The arc resistant synchronous transfer control system also includes a plurality of synchronous transfer control components housed within the main housing, the synchronous transfer control components including: (i) a hard bussed first bus structured to be coupled to a first power source, (ii) a second power source, and (iii) a hard bussed second bus, wherein an output of the second power source is able to be selectively coupled to the second bus, wherein the first bus is able to be selectively and individually coupled to each of the motors, and wherein the second bus is able to be selectively and individually coupled to each of the motors. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A full understanding of the disclosed concept can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which: 
         FIG. 1  is a schematic diagram of an arc resistant synchronous transfer control system  2  for controlling the operation of multiple electric motors according to an exemplary embodiment of the present invention; 
         FIG. 2  is a front view of arc resistant enclosure of the arc resistant synchronous transfer control system according to an exemplary embodiment of the present invention; and 
         FIGS. 3A ,  3 B and  3 C are isometric, front and left side views, respectively, of an arc resistant sub-enclosure forming part of the arc resistant enclosure of  FIG. 2 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Directional phrases used herein, such as, for example, left, right, front, back, top, bottom and derivatives thereof, relate to the orientation of the elements shown in the drawings and are not limiting upon the claims unless expressly recited therein. 
     As employed herein, the term “fastener” refers to any suitable connecting or tightening mechanism expressly including, but not limited to, screws, bolts and the combinations of bolts and nuts (e.g., without limitation, lock nuts) and bolts, washers and nuts. 
     As employed herein, the statement that two or more parts are “coupled” together shall mean that the parts are joined together either directly or joined through one or more intermediate parts. 
     As employed herein, the term “number” shall mean one or an integer greater than one a plurality). 
     As employed herein, the terms “hard bus”, “hard bussed” or “hard bussing” shall refer to a system of one or more electrical conductors that makes a common connection between a number of circuits or circuit components and that employs metallic, e.g., copper, brass or aluminum, strips or bars that are connected, e.g., bolted, together, as opposed to a cable or cables that are strung together to interconnect a number of circuits or circuit components (which is usually used for field connections). 
       FIG. 1  is a schematic diagram of an arc resistant synchronous transfer control system  2  for controlling the operation of multiple electric motors according to an exemplary embodiment of the present invention. System  2  includes a plurality of electric motors  4 . In the illustrated embodiment, five motors  4  (labeled  4 A- 4 E) are provided. It will be understood, however, that more or less motors  4  may be provided within the scope of the present invention. System  2  further includes a main power source  6 , which in the exemplary embodiment is a 4160 V, 60 Hz main power line (e.g., the 60 Hz utility supply). 
     As seen in  FIG. 1 , system  2  includes an arc resistant enclosure  8  that is structured to withstand an internal fault without endangering an operator who is standing in front of the equipment. In the exemplary embodiment, arc resistant enclosure  8  is structured to meet IEEE C37.20.7 standards, and thus be arc resistant at the front, sides and rear thereof, and to have the following arc resistant ratings: 50 kA - 0.5 s, Type 2B. 
     System  2  further includes a number of components that are provided in arc resistant enclosure  8 . In particular, system  2  includes a main bus  110  that is directly coupled to main power source  6 , and a secondary bus  12 . In the exemplary embodiment, main bus  10  and secondary bus  12  are both hard bussed, and are made of, for example and without limitation, hard copper bus bars. As seen in  FIG. 1 , the input of a reduced voltage starter device  14  is coupled to main bus  10 . In the exemplary embodiment, reduced voltage starter device  14  is a VFD. It will be understood, however, that reduced voltage starter device  14  may also take on other forms, such as a soft starter, or a VFD with a reduced voltage solid state (RVSS) bypass. As is known, this latter implementation employs both a VFD and an integral soft starter in a bypass configuration that allows the system to continue to run (via the soft starter) in the event that the VFD fails. In one particular exemplary embodiment, reduced voltage starter device  14  is an arc resistant VFD. The output of reduced voltage starter device  14  is coupled to an output isolation contactor  16 , which in turn is coupled to secondary bus  12 . 
     In addition, each motor  4 A- 4 E is coupled to main bus  10  through an associated bypass contactor  18 A- 18 E and bypass line  20 A- 20 E. Each motor  4 A- 4 E is also coupled to secondary bus  12  through an associated motor select contactor  22 A- 22 E and motor select line  24 A- 24 E. In the exemplary embodiment, bypass lines  20 A- 20 E and motor select lines  24 A- 24 E also hard bussed. 
     As noted above, in the exemplary embodiment, reduced voltage starter device  14  is a VFD in order to implement a synchronous transfer control system. In system  2 , such a VFD accelerates the selected one of the motors  4 A- 4 E to any frequency the user wants between 0 and 60 Hz. This speed control is one of the main advantageous features of a VFD. In system  2  implemented as a synchronous transfer control system, the VFD is told by the user (through a controller (e.g., PLC) coupled to the VFD) to synchronize with the applied line power on main line  10 . The VFD then accelerates the selected one of the motors  4 A- 4 E to 60 Hz, and then aligns the phase angle between the line power on main line  10  and the selected one of the motors  4 A- 4 E to 60 Hz. When the selected one of the motors  4 A- 4 E is in “sync” with applied line power on main line  10 , the transfer occurs. Referring to  FIG. 1 , the sequence of operation of system  2  is thus as follows for a normal start. First, the user calls for a start of a selected one of the motors  4 A- 4 E. In response, motor select contactor  22 A- 22 E of the selected one of the motors  4 A- 4 E is closed, and reduced voltage starter device  14  is started. The first action of reduced voltage starter device  14  is to close output isolation contactor  16 . This will result in the selected one of the motors  4 A- 4 E being connected to reduced voltage starter device  14  though the closed output isolation contactor  16  and closed motor select contactor  22 A- 22 E. During this process, the bypass contactors  18 A- 18 E remain open. Reduced voltage starter device  14  energizes and ramps the selected one of the motors  4 A- 4 E. When the ramping is complete, reduced voltage starter device  14  aligns with main bus  10 , and closes the bypass contactor  18 A- 18 E of the selected one of the motors  4 A- 4 E, and turns itself off. Finally, output isolation contactor  16  the motor select contactor  22 A- 22 E of the selected one of the motors  4 A- 4 E is opened. Reduced voltage starter device  14  is now available to start another one of the motors  4 A- 4 E. 
       FIG. 2  is a front view of arc resistant enclosure  8  showing certain components that are provided in arc resistant enclosure  8 . As seen in  FIG. 2 , arc resistant enclosure  8  is made up of a number of a number arc resistant sub-enclosures  9  (labeled  9 A- 9 E in the exemplary embodiment), and an arc resistant sub-enclosures  11 , which are described in detail below. The arc resistant sub-enclosures  9  and the arc resistant sub-enclosures  11  are positioned immediately next to one another to form arc resistant enclosure  8 , with each one of the arc resistant sub-enclosures  9 A- 9 E corresponding to one of the motors  4 A- 4 E. 
       FIGS. 3A ,  3 B and  3 C are isometric, front and left side views, respectively, of one of the arc resistant sub-enclosure  9  (i.e., one of  9 A- 9 E) showing certain components that are provided therein. Each arc resistant sub-enclosure  9  includes a main housing  26  which houses a number of the components of system  2 , and an arc plenum  28 . Main housing  26  includes a front portion  32 , a rear portion  34 , a right side portion  36 , a left side portion  38 , and an open top portion  40 . Arc plenum  28  is attached to top portion  40  of main housing  26 . Front portion  32 , rear portion  34 , right side portion  36 , and left side portion  38  each include one or more enclosure members (e.g., a wall or cover with corner bracing) made of a material having arc resistant ratings of 50 kA-0.5 s, Type 2B, such as, without limitation, 12 gauge mild (low carbon) steel. In  FIGS. 3A and 3B , one such member is removed from front portion  32  in order to show the internal compartment  30  of main housing  26 . 
     Arc plenum  28  has a front portion  42 , a rear portion  44 , an open right side portion  46 , an open left side portion  48 , a top portion  50 , and an open bottom portion  52 . Front portion  42 , rear portion  44  and top portion  50  each include one or more enclosure members (e.g., a wall or cover with corner bracing) made of a material having arc resistant ratings of 50 kA-0.5s, Type 2B, such as, without limitation, 12 gauge mild (low carbon) steel. Arc plenum  28  (and therefore internal compartment  30  of main housing  26 ) is structured to be fluidly connected to a venting/duct system, similar to an HVAC duct, via open right side portion  46  and/or open left side portion  48 . Arc resistant sub-enclosures  11  is similar in structure to arc resistant sub-enclosure  9  as just described. When arc resistant sub-enclosures  9 A- 9 E and  11  are positioned adjacent one another as shown in  FIG. 2 , the arc plenums  28  are coupled to one another and then to venting/duct system. 
     As seen in  FIG. 2  and  FIGS. 3A ,  3 B and  3 C, at least the following components of system  2  are housed within arc resistant enclosure  8  in a manner such that they are configured to operate as shown in  FIG. 1 : main bus  10 , secondary bus  12 , reduced voltage starter device  14 , output isolation contactor  16 , bypass contactors  18 A- 18 E and motor select contactors  22 A- 22 E. More specifically, a portion of main bus  10 , a portion of secondary bus  12 , reduced voltage starter device  14 , and output isolation contactor  16  are housed within the internal compartment of main housing  26  of arc resistant sub-enclosure  11 , and a portion of main bus  10 , a portion of secondary bus  12 , a respective one of the bypass contactors  18 A- 18 E and a respective one of motor select contactors  22 A- 22 E are housed within the internal compartment of main housing  26  of each arc resistant sub-enclosure  9 . 
     Arc resistant enclosure  8  thus functions as an arc resistant enclosure that meets IEEE C37.20.7 standards for system  2 , In operation, in the case of a failure of system  23 , hot gasses and/or pressure waves will be vented up main housing  26  and through arc plenum(s)  28  to the associated venting/duct system (and thus away from personnel). In addition, such personnel will be protected/shielded from such hot gasses and/or pressure waves by the enclosure members of main housing  26  and arc plenum  28 . 
     In one embodiment, multiple arc resistant enclosures  8  may be placed side by side to one another in a configuration wherein the arc plenums  28  thereof are in communication with one another (the left side portion  48  of one being adjacent the right side portion  46  of another, and so on) so as to provide an escape-way for hot gasses and/or pressure waves in the event of a failure of one or more of the arc resistant enclosures  8 . 
     While specific embodiments of the disclosed concept have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the disclosed concept which is to be given the full breadth of the claims appended and any and all equivalents thereof.