Patent Application
20060012954
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.
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.
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:
As shown in
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 54A, 54B, 54C for each pair of line and load buses 30, 32 associated with a pole of the circuit breaker 20. Additionally, the propeller fans 54A, 54B, 54C 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
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.
