Patent Application
20140054271
The present invention relates generally to electrical power distribution systems and, more particularly, to protecting feeder circuits in a multi-phase power distribution system from arcing faults while also containing the arcing, dissipating the fault current to extinguish the arcing, and isolating the feeder circuit in which the fault occurred.
Typical devices used to reduce available energy from an arc flash event, over-current event or arc fault will short out the electrical circuit while waiting for an upstream circuit to open and isolate the circuit. During this delay, considerable damage can be done by the energy being dissipated from the event that triggered the short.
When multiple feeder circuits are supplied with power from a common supply bus, circuit breakers are typically provided in each of the feeder circuits in addition to the main circuit breaker in the common supply bus. If the main circuit breaker trips before the circuit breaker of the feeder circuit in which the fault occurred, power can be unnecessarily lost in even the feeder circuits that were not affected by the fault condition.
The present invention avoids such problems by providing a three-phase disconnect switch for a power distribution system that supplies three-phase power from a source through a main circuit breaker to multiple three-phase feeder circuits. In one embodiment, the switch includes three pairs of contacts adapted for connection to the three phase lines of a selected one of the feeder circuits for opening and closing each of the phase lines, and a movable actuator associated with the three pairs of contacts and responsive to a signal indicating the occurrence of an arcing fault in the selected feeder circuit for initially creating a short circuit across the three phase lines of the feeder circuit and then opening the contacts to isolate the feeder circuit in which the fault occurred
In one implementation, each feeder circuit is provided with a separate disconnect switch that responds to the detection of an arcing fault condition in that feeder circuit to instantly interrupt the supply of power to that feeder circuit while also transferring the fault current to the disconnect switch where any arcing is quickly controlled and extinguished within a protected cavity. The instant isolation of the feeder circuit in which the fault occurred reduces damage to downstream equipment, while the arc suppression protects both equipment and personnel from damage or injury that might otherwise be caused by the arcing.
One application for the disconnect switch is in a three-phase power distribution system that supplies three-phase power from a source through a main circuit breaker to multiple feeder circuits, each of which has a feeder circuit breaker downstream of the main circuit breaker, and a fault detector for producing an output signal in response to the occurrence of a fault in the corresponding feeder circuit. The normally closed contacts of the disconnect switch are located between the main circuit breaker and the feeder circuit breaker, and the actuator associated with the contacts is responsive to an output signal from the fault detector for initially shorting the three phase conductors in that feeder circuit and then opening the feeder circuit.
In one implementation, the actuator includes a plurality of spaced conductive areas for dividing arcs across the disconnect switch as the switch is opened by the actuator, thereby reducing the arc voltage until the arcs are extinguished.
The invention may best be understood by reference to the following description taken in conjunction with the accompanying drawings, in which:
Although the present disclosure is described in connection with certain aspects and/or embodiments, it will be understood that the present disclosure is not limited to those particular aspects and/or embodiments. On the contrary, the present disclosure is intended to cover all alternatives, modifications, and equivalent arrangements as may be included within the spirit and scope of the present disclosure as defined by the appended claims.
Turning now to the drawings and referring first to
In the embodiment illustrated in
As can be seen in
In
To permit movement of the actuator plate 20 between its retracted and advanced positions, the plate 20 is slidably mounted between two dielectric guide plates 30 and 31. Movement of the actuator plate 20 is effected by a linear electrical actuator 32 attached to the outboard end of the plate 20, so that advancing and retracting movement of the plate 20 may be controlled by electrical signals that control the energization and de-energization of the linear actuator 32. Such actuators are commercially available, such as the “Quickshaft” linear DC servomotors available from Dr. Fritz Faulhaber GMBH & Co.
The contacts 21 and 22 are both curved away from each other on both sides of the point where they contact each other when the switch is closed. This creates a tapered entry for the front edge of the actuator plate 20 as it is advanced between the two contacts. The leading edge portion 25 of the actuator plate 20 is wedge-shaped, and the tapered surfaces of the wedge engage the curved contacts 21, 22 and cam them away from each other, against the forces of the biasing springs 23, 24. In the fully advanced position, depicted in
As depicted in
As the actuator plate 20 continues to advance between the three pairs of opened contacts 21, 22, the leading edge portion 25 of the plate 20 plate becomes disengaged from all the contacts, thereby breaking the momentary short circuit across the three phase lines. At this point the fault current produces arcs between the crowbar front edge of the plate 20 and the movable contacts 21, 22. As the plate continues to advance, the arcs across any given pair of opened contacts 21, 22 are attracted to two sets of conductive arc plates 26a-26e and 27a-27e on the top and bottom surfaces of the actuator plate 20, as those arc plates sequentially pass between the three pairs of contacts 21, 22. Specifically, three identical sets of arc plates 26a-26e are formed on the top surface of the actuator plate 20, and three identical sets of arc plates 27a-27e are formed on the bottom surface of the actuator plate 20. Dielectric partitions 28 and 29 separate adjacent sets of the arc plates 26a-26e from each other on the upper surface of the plate 20, and those partitions wrap around the leading edge of the plate 20 and continue along the lower surface of the plate 20 to separate adjacent sets of the arc plates 27a-27e from each other on the lower surface. Because the arcs from any given pair of contacts 21, 22 are attracted to all the arc plates on the corresponding segment of the actuator plate 20, the spaced arc plates progressively divide the arcs and thereby reduce the arc voltage until the arcs become extinguished. This occurs so quickly that the arcs are extinguished before the main circuit breaker 10 can trip, so there is no interruption of the power being supplied to the various feeder circuits not affected by the arc fault.
Because of the curvature of the contacts 21, 22 in each of the three pairs, the spaces between the contacts and each successive arc plate progressively diminish as the actuator plate 20 advances between the three pairs of contacts. Thus the lengths of the arc segments attracted to successive arc plates are gradually reduced until those segments are extinguished as the arc plates successively engage the adjacent contact.
To contain the arcing that occurs within the disconnect switch 14, the contacts 21, 22 and the portion of the actuator plate 20 that interacts with those contacts are contained within a cavity 40 formed by a dielectric housing having upper and lower sections 41 and 42 laminated against the two guide plates 30 and 31. Thus, the energy of the current transferred from the arc fault to the disconnect switch is contained and dissipated within the cavity 40, so that it cannot do any damage.
Although the illustrative embodiment of the invention described above utilizes arc fault detectors to detect occurrences of arc faults in the feeder circuits, the disconnect switches could respond to signals produced in response to over-current events. It will also be understood that the disconnect switches may be either resettable switches or switches that require servicing after each occurrence of a fault that causes the actuation of one of the disconnect switches.
While particular aspects, embodiments, and applications of the present disclosure have been illustrated and described, it is to be understood that the present disclosure is not limited to the precise construction and compositions disclosed herein and that various modifications, changes, and variations may be apparent from the foregoing descriptions without departing from the spirit and scope of the present disclosure as defined in the appended claims.
