Patent Publication Number: US-2006012954-A1

Title: Network protector added load ability through forced convection

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to network protectors and, more specifically, to a network protector having a convection cooling assembly disposed within the network protector housing.  
      2. Background Information  
      Secondary power distribution networks consist of interlaced grids which are supplied by two or more sources of power so that the loss of a single source of power will not result in an interruption of service. Such networks provide the highest level of reliability possible with conventional power distribution and are normally used to supply high-density load areas such as a section of a city, a large building, or an industrial site. Between the power sources and the network are a transformer and a network protector. Such network protectors are often found in dust-proof or moisture-proof housings which are disposed in subterranean passageways in large metropolitan areas. The housing, or “tank,” may be further disposed within a concrete vault.  
      The primary components of the network protector are a circuit breaker and a control compartment. The control compartment includes components, such as a relay, to sense the transformer and network voltages and line currents, and to execute algorithms to initiate breaker tripping or closing action. Trip determination is based on detecting an over current condition or reverse power flow, that is, power flow from the network to the energy source. The buses connecting the circuit breaker to the line and load are typically disposed at the back of the housing and extend upwardly towards the top on the housing. Typically, the circuit breaker is a three-phase circuit breaker wherein each phase has a bus. As electricity passes through each bus heat is created. Generally, the buses are the hottest component in the network protector.  
      To dissipate the heat in the buses, the buses connecting the circuit breaker to the transformer and the circuit breaker to the load typically have a hollow square cross-section or consist of spaced laminations. These shapes increase the surface area, and therefore the thermal emissivity, of the bus. Additionally, these shapes allowed air to flow through the bus and remove heat by convection. Such heat dissipation means are generally sufficient for normal use of the circuit breaker.  
      Network protectors, however, are subject to their maximum current rating at peak times of service. The maximum current rating of the circuit breaker is limited by, among other factors, its maximum thermal rating. Thus, the maximum current rating of the circuit breaker could be increased if the maximum thermal rating were increased. The maximum thermal rating could be increased if the heat created in the bus assembly was dissipated at a greater rate. Moreover, if the maximum current rating of the circuit breaker could be increased, a circuit breaker that presently has a lower current rating could be used in the network protector. Generally, circuit breakers with lower current ratings are smaller and less expensive. Thus, if heat dissipation in a present network protector enclosure could be increased, the network protector could utilize a smaller and less expensive circuit breaker.  
      There is, therefore, a need for a network protector structured to dissipate heat.  
      There is a further need for a network protector convection cooling assembly structured to increase the cooling of the network protector housing buses.  
      There is a further need for a network protector convection cooling assembly that may be used in network protector housings currently in use.  
     SUMMARY OF THE INVENTION  
      These needs, and others, are met by the present invention which provides a convection cooling assembly, such as a fan, structured to move air over the network protector buses. The increased fluid flow over the buses increases the amount of heat lost though convection. In the preferred embodiment, the convection cooling assembly is a directional fan, such as a propeller fan, structured to move air directly over the buses. It is also preferred that the fan be located at the bottom of the enclosure and direct airflow from the bottom of the enclosure upwardly over the buses. This allows the cooler air located at the bottom of the enclosure to move over the buses. In a more preferred embodiment, there is an individual fan for each pair of buses in the enclosure. While the fans may run continuously, the invention also provides for a control assembly that senses a characteristic of the network protector, such as, the current flowing through the circuit breaker, and activates the fans at a preset limit. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      A full understanding of the invention 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 front view of a network protector having a convection cooling assembly.  
       FIG. 2  is a side view of a network protector having a convection cooling assembly.  
       FIG. 3  is a side view of an alternate embodiment of a network protector having a convection cooling assembly. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      As shown in  FIGS. 1 and 2 , a network protector  10  includes a housing assembly  12  structured to form an enclosure with a movable door  14 . The housing assembly  12  is structured to be placed within a vault  16 . A vault  16  is typically made of concrete or a similar material. The two primary network protector components, a circuit breaker  20  and a control assembly  22  are disposed within the housing assembly  12 . The circuit breaker  20  includes at least one set of main contacts  24  (shown schematically,  FIG. 2 ) that are structured to move between a first, open position and a second, closed position. When the main contacts  24  are in the second, closed position, electricity may flow through the circuit breaker  20 . When the main contacts  24  are in the first, open position, electricity cannot flow through the circuit breaker  20 . The circuit breaker  20  also includes an operating mechanism  26  (shown schematically) that is structured to move the main contacts  24  between the first and second position. The main contacts  24  are coupled to one or more network protector load buses  30  and one or more network protector line buses  32  which are part of a bus assembly  31 . The bus assembly  31  is coupled to an interior wall of the housing assembly  12 , preferably the back wall. In a preferred embodiment, the circuit breaker  20  is a three-phase circuit breaker having three poles. Each pole includes a pair of buses, a load bus  30  and a line bus  32 . The bus assembly  31  is disposed near the back of the housing assembly  12 . The circuit breaker  20  is disposed at about mid-level within the housing assembly  12  and the load buses  30  and the line buses  32  extend generally upwardly therefrom.  
      The network protector  10  also includes a convection cooling assembly  50 . The cooling assembly  50  is structured to move air over the load buses  30  and the line buses  32  to increase to amount of heat transfer through convection. In the preferred embodiment, the convection cooling assembly  50  includes at least one fan  52  disposed adjacent to the load buses  30  and the line buses  32 . The fan  52  is, preferably, a propeller fan  54  having a propeller  56  mounted on an axle (not shown). The propeller fan  54  is structured to move air in a direction generally parallel to the axis of the propeller. The propeller fan  54  is positioned to move air directly toward the load buses  30  and the line buses  32 . The fan  52  may be disposed on a mounting bracket  58  that is coupled to the back side of the control assembly  22 . In a more preferred embodiment, there is a propeller fan  54 A,  54 B,  54 C for each pair of line and load buses  30 ,  32  associated with a pole of the circuit breaker  20 . Additionally, the propeller fans  54 A,  54 B,  54 C are disposed adjacent to the bottom of the housing assembly  12  and structured to move air upwardly from the bottom of the housing assembly  12  and over the load buses  30  and the line buses  32 .  
      While the fan  52  may run continuously, the control assembly  22  may also include a fan control  60  structured to activate the fan  52  when a characteristic of the network protector  10  exceeds a pre-set limit and deactivate the fan  52  when the characteristic drops below a pre-set limit. The characteristic is preferably selected from the following: the current through the circuit breaker  20 ; the temperature of the bus assembly  31 ; the temperature of the circuit breaker  20 ; or the temperature within the housing assembly  12 .  
      In another embodiment, shown in  FIG. 3 , the fan  52  is an exhaust fan  70 , such as a centrifugal fan, disposed on top of the housing assembly  12 . In this embodiment, air is drawn over the load buses  30  and the line buses  32 . That is, in addition to the exhaust fan  70 , the convection cooling assembly  50  includes an air inlet assembly  72 . The air inlet assembly  72  is structured to provide a passage for air to enter the housing assembly  12  at a location adjacent to the bottom of the load buses  30  and the line buses  32 . In one embodiment, the air inlet assembly  72  is one or more openings  74 A disposed along the bottom of the housing assembly  12 , preferably below the load buses  30  and the line buses  32 , or one or more openings  74 B through the back wall of the housing assembly  12  adjacent to the bottom of the load buses  30  and the line buses  32 . However, because network protectors  10  are often disposed in subterranean locations, it is often desirable to not have openings in lower portions of the tank as such openings may let in water. Accordingly, the air inlet assembly  72  may also be a snorkel  76 . The snorkel  76  includes a hollow tube  78  having an upper opening  80  disposed outside of the housing assembly  12  adjacent the top of the housing assembly  12  and one or more lower openings  82 . The tube  78  extends from the upper opening  80  to a location adjacent the bottom of the load buses  30  and the line buses  32 . The lower openings  82  are at the end of the tube  78  opposite the upper opening  80 . In operation, the exhaust fan  70  draws air out of the housing assembly  12 . As air is withdrawn from the housing assembly  12 , the air is replaced by air entering the housing assembly through the inlet assembly  72 . Thus, as air is drawn from the inlet assembly  72  to the exhaust fan  70 , there is an airflow over the load buses  30  and the line buses  32 . As with the propeller fan  54  described above, there may be one exhaust fan  70  for each pole of the circuit breaker  20 . However, it is preferred to have a single exhaust fan  70  and allow the inlet assembly  72  to direct air over each pair of load buses  30  and line buses  32 . For example, the snorkel  76  may have a cross bar so that the lower opening  82  may be disposed below each pair of load buses  30  and line buses  32 .  
      While specific embodiments of the invention 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 invention which is to be given the full breadth of the claims appended and any and all equivalents thereof.