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 vertical elevation view of an indicating cable limiter including a replaceable fusible element with fixed and removable boots cut away to show internal structures in accordance with an embodiment of the invention.
FIG. 2 is a plan view of the indicating cable limiter of FIG. 1, except that the replaceable fusible element has been removed to show internal structures.
FIG. 3 is a vertical elevation view of a portion of an indicating 5-way/5-way crab limiter including a number of different replaceable fusible elements with fixed and removable boots cut away to show internal structures in accordance with another embodiment of the invention.
FIG. 4 is a simplified isometric view of the entire 5-way/5-way crab limiter of FIG. 3.
FIG. 5 is a block diagram in schematic form of a power supply and LED indicating circuit for a cable limiter in accordance with another embodiment of the invention.
FIG. 6 is a block diagram in schematic form of a power supply and piezoelectric transducer for a cable limiter in accordance with another embodiment of the invention.
FIG. 7 is a block diagram in schematic form of a power supply and wireless transmitter for a cable limiter in accordance with another embodiment of the invention.
FIG. 8 is an isometric view of the cable limiter of FIG. 1 with the second boot removed from the main body to show internal structures.
FIGS. 9A-9C are vertical elevation views of cable limiters in accordance with embodiments of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
As employed herein, the term “number” shall mean one or an integer greater than one (i.e., a plurality).
As employed herein, the term “wireless” shall expressly include, but not be limited by, radio frequency (RF), light, visible light, infrared, ultrasound, wireless area networks, such as, but not limited to, IEEE 802.11 and all its variants (e.g., without limitation, 802.11a; 802.11b; 802.11g), IEEE 802.15 and all its variants (e.g., without limitation, 802.15.1; 802.15.3, 802.15.4), IEEE 802.16 and all its variants, other wireless communication standards (e.g., without limitation, ZigBee™ Alliance standard), HyperLan, DECT, PWT, pager, PCS, Wi-Fi, Bluetooth™, and cellular.
As employed herein, the term “cable limiter” means a power conductor limiter apparatus including a fusible element.
As employed herein, the terms “crab limiter” or “crab” mean a power conductor limiter apparatus including a plurality of fusible elements for a plurality of power conductors.
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.
EXAMPLE 1
Referring to FIGS. 1 and 2, a cable limiter apparatus 2 is shown. A conductive tube 4,6 (e.g., without limitation, made of tin coated copper) is molded into each end of a compound (e.g., without limitation, made of high temperature, heat resistant, cycloaliphatic resin), which makes up the main body 8 of the cable limiter apparatus 2. The apparatus 2, in turn, houses a replaceable fusible element 10. The two tubes 4,6 serve as cable crimp areas for power cables, such as 12′,12 (shown partially within the tubes 4,6 of FIG. 1), respectively. These tubes 4,6 are brazed into conductive end pieces 14,16 (e.g., without limitation, made of brazed copper), respectively, that serve as the mounting points for the replaceable fusible element 10. Two screws 18 (e.g., without limitation, stainless steel, angle point end, Allen head) (only two total screws 18 are shown in FIG. 1) in each of the end pieces 14,16 provide the compressive force needed to secure the replaceable fusible element 10 into the main body 8 through the apertures 15,17 of the end pieces 14,16 and the apertures 19,21, respectively, of the replaceable fusible element 10.
The replaceable fusible element 10 is located within a cavity 20 of the main body 8. The replaceable fusible element 10 is preferably enclosed in a suitably high temperature, high silica resin that can absorb the thermal shock of fuse interruption without significant collateral damage occurring to the main body 8. Preferably, each different size of various different fusible elements (e.g., 10,10′,10″ of FIGS. 9A-9C) is interlocked by a corresponding different molded member (e.g., without limitation, tab 22 for element 10) made of the high temperature, high silica resin. For this molded tab 22, a corresponding mating aperture (e.g., without limitation, slot 24) is provided in the cavity 20 of the main body 8, such that only the correctly sized (i.e., proper current rating) fusible element 10 can be placed in that cavity 20. Preferably, the ends of the end pieces 14,16 have a circular cross-section (not shown) with a slot 25 along a diameter to receive one corresponding end of the fusible element 10.
Two boots 26,28 (e.g., without limitation, made of silicone rubber) fit over each end of the main body 8. One end has the first boot 26 fixed to protect an annunciator portion 30. The other end has the second boot 28, which is removable from the main body 8. After a clamp 32 (e.g., without limitation, made of a stainless steel, non-magnetic material) is removed or loosened (FIG. 8), the removable boot 28 can be slid down the power cable 12 (to the right of FIG. 1), which has been fixedly crimped into the tube 6 at that end. By removing the removable boot 28, access to the various hold-down screws 18 is provided. In turn, the spent replaceable fusible element 10 can be removed and a new replaceable fusible element (not shown) of only the correct size can be placed into the main body cavity 20. Then, the removable boot 28 can be repositioned (as shown in FIG. 1) and the same clamp 32 (best shown in FIG. 8) (shown in cross-section in FIGS. 1-2 for convenience of illustration) can be tightened in order to make a watertight seal between the two boots 26,28.
EXAMPLE 2
FIGS. 9A, 9B and 9C show different replaceable fusible elements 10,10′,10″ including different tabs 22,22′,22″ for 4/0, 500 MCM and 750 MCM applications, respectively. In this manner, the tabs 22′ and 22″ are not suitable for the cable limiter 2 of FIG. 1 because, unlike the tab 22, these tabs 22′,22″ do not mate with the slot 24.
EXAMPLE 3
As shown in FIGS. 3 and 4, as an extension of the cable limiter apparatus 2 of FIGS. 1 and 2, a 5-way/5-way crab limiter 40 has five cable limiter sections 42,44,46,48,50 on one side and 52,54,56,58,60 on the opposite side emanating from each side of a conductive collector plate 62 (e.g., without limitation, made of solid copper with plural brazed copper conductive end pieces, such as 64). There is one input cable and one output cable on each side of the crab limiter 40 that feed four other cables on each side. Hence, there are ten cables in all, five on each side. Effectively, the crab limiter 40 includes ten cable limiters, as each is described above, having a conductive end piece 64 (e.g., without limitation, made of brazed copper) (which holds a sensing circuit 66 and one or more printed circuit boards (PCBs) 68 associated with annunciation of status (e.g., non-operated or conductive; operated or open) of the corresponding replaceable fusible element 70) mounted to the collector plate 62. The ten cable limiters may have the same or different current ratings. The main body 72 of each limiter section of the crab limiter 40 is preferably made from a high temperature, cycloaliphatic resin and incorporates a cavity 74 to accept the replaceable fusible element 70. The collector plate 62 and part of the main body 72 are preferably covered with high temperature silicone rubber 76. Each limiter section has a removable boot 78 (e.g., without limitation, made of silicone rubber) and a clamp 80 (e.g., without limitation, made of a stainless steel non-magnetic material) (shown in cross-section for convenience of illustration) to make the assembly watertight.
EXAMPLE 4
Referring again to FIGS. 1 and 2, one side of the end piece 14 includes an opening 82 to accept a PCB 84 that contains, for example, electronic components 86 (FIG. 5) providing a power regulator 88 and driver 90 suitable to output a desired voltage and current to operate an annunciator 91 (e.g., a visual indicator, such as the example bright white light emitting diode (LED) 92). An example of a power regulator including a self-powered inductive coupling circuit and regulator circuit is disclosed in U.S. Patent Application Publication No. 2006/0076946, which is incorporated by reference herein.
The example LED 92 is located such that it points outward from the cable limiter apparatus 2. Next to the PCB 84 is a parasitic air core sensor 94 that encircles the end piece 14 which is electrically connected to a power cable 12′. This air core sensor 94 supplies voltage to the power regulator 88. The air core sensor 94, the power regulator 88 and driver 90 are preferably encapsulated in the high temperature, heat resistant cycloaliphatic resin compound that makes up the main body 8 of the cable limiter apparatus 2.
The extended tip of the LED 92 passes through the surface of the main body 8. The LED 92 is illuminated when suitable power flow passes from one end of the cable limiter terminal (e.g., tube 4) to the other cable limiter terminal (e.g., tube 6). If the replaceable fusible element 10 operates and opens for any reason, then the LED 92 is extinguished, thereby indicating to maintenance personnel that the replaceable fusible element 10 needs to be changed.
For example, fiber optic cables (not shown) can be connected to the output of the LED 92 and mounted at a convenient point for maintenance personnel to check multiple cable limiters (not shown) in any one location. This convenient point could be at the access portal of an underground vault (not shown), or the manhole entry (not shown) or the doorway (not shown) into an underground vault.
EXAMPLE 5
A suitable annunciator 100 (e.g., an audio annunciator, such as a piezoelectric transducer 102) is shown in FIG. 6. An output audio signal 104 is advantageously employed since the cable limiter apparatus 2′ is normally located underground in a network vault (not shown) or below a manhole (not shown). The audio signal 104 may be reported, for example, by a passing citizen or by regular inspections by a maintenance crew from a power distribution company. The cable limiter apparatus 2′ of this example is nearly the same as the apparatus 2 as described above in connection with the LED 92 of FIGS. 1 and 2. Other than the different audio annunciator 100, the only difference is that there are potential (voltage sense) conductors 106,108 that are electrically connected to the end pieces 14,16 on each side of where the replaceable fusible element 10 mounts within the limiter main body 8 (FIG. 1). These conductors 106,108 are electrically connected to the electronics of a suitable circuit, such as AC/DC power supply 110, that drives the piezoelectric transducer 102. In operation, whenever the replaceable fusible element 10 operates and opens, a voltage difference is measured across the now open fusible element. This voltage supplies the operating power for AD/DC power supply 110, which permits the piezoelectric transducer 102 to be energized and heard (e.g., without limitation, as a “chirp”). For example, the piezoelectric transducer 102 is pulsed approximately once every second or at some suitable rate and suitable volume dependent upon the voltage difference sensed across the open fusible element 10. This embodiment supplies the audible signal 104 that is suitable for a below grade, underground vault (not shown). After the maintenance crewperson enters the underground vault, he/she follows the sound to pinpoint the location of the fusible element 10 that has operated.
EXAMPLE 6
In the example of FIG. 7, the annunciator 120 is provided by wireless communication to a remote location. A wireless transmitter 122 is powered, for example, from a voltage sense circuit formed by the AC/DC power supply 110 connected across the replaceable fusible element 10. The power supply 110 supplies voltage to power the wireless transmitter 122, which is part of the main body 8 (FIG. 1) of the cable limiter apparatus 2″, only after the replaceable fusible element 10 has operated and opened. The wireless transmitter 122 cooperates with a corresponding wireless receiver 124 mounted in suitably close proximity to the wireless transmitter 122 (e.g., within the same confines as the underground vault (not shown)). The wireless receiver 124 serves as a data concentrator for wireless signals 126,128,130,132 from various connected wireless transmitters/cable limiters in any one location, and re-transmits the information over a suitably longer range wireless system 134 (e.g., without limitation, Cellnet™; any suitable cellular network system; any suitable wireless system) through wireless signal 136. A head-end system 138 receives any calls by exception (i.e., calls which now indicate that the replaceable fusible element 10 has operated and cleared) and gives a unique location indicator code 140, which uniquely pinpoints the cable limiter's location on the power distribution system.
The disclosed cable limiter apparatus 2,2′,2″ preclude the necessity to remove an entire spent cable limiter, strip cable insulation, and re-crimp and install a new cable limiter. Only the replaceable fusible element 10 needs to be replaced after it clears the power circuit when the downstream power cable 12, which is fed by the upstream cable limiter or crab limiter section, faults either phase-to-phase or phase-to-ground.
The disclosed cable limiter apparatus 2,2′,2″ include removable spent limiter sections 10 that may be removed and replaced during the repair of the power circuit cable(s) 12,12′.
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 the invention which is to be given the full breadth of the claims appended and any and all equivalents thereof.
Patent Application
20080042796
