Apparatus and Method for Sensing Power Line Conditions

This invention relates to electrical power transmission, and more particularly, to apparatus and a method for sensing power line conditions.

In recent years, it has become common practice to sense power line conditions with a current transformer and/or a voltage transformer for the purposes of energy management, ground fault detection, and system measurement and control. A frequent use of such information about power line conditions is to optimize the power factor by means of power capacitor switching.

Typically, a current transformer and/or a voltage transformer are packaged as self-contained units which are mounted on the power pole near a power line supporting insulator. The connection to the power system is made by dead ending the power line on one side of the insulator and connecting the transformer package in series with the line. Specifically, the power line is cut, dead end clamps are installed, and the leads of the transformer package are connected to the dead end clamps. It is difficult, if not impossible, to carry out this installation procedure while the power line is "hot", i.e., carrying electrical power.

According to one aspect the invention a line condition sensing device, e.g. a current transformer and/or a voltage transformer, is incorporated into the body of a pole mounted, power line supporting insulator. Specifically, a line condition sensing device is embedded in the insulator to form an integral unit therewith. One end of the insulator carries a pole mounting base. The other end of the insulator carries a power line receiving clamp. A substantial weight and space reduction results because of the use of the power line supporting insulator as a housing for the line condition sensing device.

According to another aspect of the invention, a line condition sensing device is connected in parallel with a power line to permit conditions to be monitored without cutting or dead ending the line. Preferably, the condition sensing device is connected to the "hot" intact power line by means of taps. If the line condition sensing device is incorporated into the power line supporting insulator, as described in the preceding paragraph, the device is preferably installed on a hot line by opening the power line receiving clamp of the original insulator, holding the power line in spaced relationship from the original insulator while replacing it with the new insulator, resecuring the power line on the clamp of the new insulator, and then connecting the taps to the hot power line. A feature of this aspect of the invention is the use of a choke around the segment of the power line between the taps so as to divert the majority of the current carried by the line through the line condition sensing device.

A specific embodiment of the best mode contemplated of carrying out the invention is illustrated in the drawings, in which:

FIG. 1 is a side elevation view of line condition sensing apparatus incorporating principles of the invention;

FIG. 2 is a perspective view of the apparatus of FIG. 1 mounted vertically on the crossarm of a power pole;

FIG. 3 is a perspective view of the apparatus of FIG. 1 mounted horizontally on a power pole;

FIGS. 4, 5, and 6 are perspective views of a power pole transmitting three phase electrical power, illustrating the preferred method for installing the apparatus of FIG. 1;

FIG. 7 is an electrical schematic diagram illustrating the connection of the apparatus of FIG. 1 to the three phase power system of FIGS. 4, 5, and 6;

FIG. 8 is a side elevation view of other line condition sensing apparatus incorporating principles of the invention;

FIG. 9 is an end elevation view of the apparatus of FIG. 8;

FIG. 10 is a side sectional view of the current and voltage sensing circuitry of the apparatus of FIG. 8;

FIG. 11 is an end sectional view of the current and voltage sensing circuitry of the apparatus of FIG. 8; and

FIG. 12 is a schematic circuit diagram of the current and voltage sensing circuitry of the apparatus of FIG. 8.

In FIG. 1 power line condition sensing apparatus comprises a current transformer 10, a voltage transformer 12, a top mounting plate 14, a pole mounting base 16, and a terminal box 18 all incorporated in a power line insulator 20 in an integral structure. Insulator 20 is preferably made from Polysil. Preferably, current transformer 10, voltage transformer 12, plate 14, base 16, and terminal box 18 are embedded in the Polysil material during the molding process for insulator 20. A conventional trunnion clamp 22 mounted on plate 14 supports the weight of a power line 24 whose conditions are to be sensed. A metal, i.e. aluminum, pipe 25, which forms part of current transformer 10, extends from opposite sides of insulator 20. An uninsulated jumper cable 26 passes through pipe 25 and is electrically connected to power line 24 by hot line taps 30 and 32, respectively. Thus, the described apparatus performs two functions--the traditional function of a power line insulator, namely to bear the weight of the power line in spaced relation from the pole, and also the function of current and voltage transformers, namely to sense the conditions of the line. The electrical connections to the power line are made without dead ending, and therefore can be established while the power line is "hot", i.e. carrying electrical power.

In FIG. 2 the apparatus of FIG. 1 is vertically mounted on a crossarm 40. The stud of base 16 passes through a hole in crossarm 32 and is secured thereto by a bolt 44.

In FIG. 3 the apparatus of FIG. 1 is horizontally mounted on a power pole 46 by a conventional horizontal mounting base. In this arrangement the mounting bolt 16 (FIG. 1) is replaced with a shorter bolt that allows attachment to a standard horizontal mounting bracket.

The preferred method for installing the described apparatus is illustrated in FIGS. 4, 5 and 6. In FIG. 4, prior to installation of the apparatus, power lines 50, 51, and 52 of a three phase power transmission system are supported on a crossarm 54 of a power pole 56 by conventional insulators 58, 59, and 60.

As illustrated in FIG. 5, power lines 50, 51, and 52 are unclamped from the insulators and lifted above crossarm 54 by an insulated boom 62 sufficiently to provide the necessary work space for removing insulators 58, 59, and 60 and mount in their place units 64, 65 and 66 of the apparatus of FIG. 1. Boom 62 temporarily supports the weight of power lines 50, 51, and 52 during the insulator replacing procedure.

As illustrated in FIG. 6 after mounting units 64, 65, and 66 on crossarm 54, boom 62 is lowered and removed, power lines 50, 51 and 52 are secured in the trunnion clamps of unit 64, 65 and 66, respectively, and the hot line taps are connected to the power lines, thereby completing the installation.

The condition sensing devices in unit 64, 65, and 66 are electrically connected through the junction boxes to a remote transceiver device (RTD) 68 of conventional design. The same holes used for insulators 58, 59, and 60 can be used to secure unit 64, 65 and 66. Because of the integral construction, very little additional weight must be carried by crossarm 54. Therefore, reinforcement of crossarm 54 is not usually required.

FIG. 7 shows an electrical schematic diagram of the connections of unit 66 to power line 52 as illustrative of the connections of the other units to the other power lines. Jumper cables 26 and 28 and the primary of current transformer 10 form a parallel circuit with the portion of power line 52 between hot line taps 30 and 32. A resistor 57 is shunted across the secondary of current transformer 10. The primary of voltage transformer 12 is connected from one side of the primary of current transformer 10 to ground. The secondary of current transformer 10 and the secondary of voltage transformer 12 are connected to RTD 68. One important application of the invention is to improve the power factor of the system. To this end, RTD 68 senses the power factor and opens and closes power switches 72, 73, and 74 to selectively switch in and out of the system capacitors 76, 77, and 78, respectively, so as to adjust the power factor.

In summary, the conditions of a power line, i.e. current and/or voltage are monitored by the same insulative apparatus that also supports the power line. The condition sensing apparatus is electrically connected without dead ending the power line. As a result, it can be installed while the power line is hot using standard hot line maintenance techniques, substituting the apparatus of the invention for standard power line supporting insulators.

In the embodiment of FIG. 8 elements, in common with the embodiment of FIG. 1 bear the same reference numerals. Current and voltage sensing circuitry represented schematically as a block 80 is embedded in the top of insulator 20. In this embodiment, no sensing circuitry is embedded in the bottom of insulator 20. A split annular choke 81 surrounds power line 24 and is connected to trunion clamp 22 by a bracket 82. Choke 81 preferably comprises an inner core made of annular alternating laminations of insulative and ferro magnetic material, such as iron, surrounded by a housing cast, for example, from aluminum. If desired, the housing could have a "hot eye" 83 to facilitate handling. During installation, to place choke 81 around power line 24, its two halves are separated and then bolted together by fasteneres 84. Choke 81 provides a large inductance that substantially blocks the flow of current through power line 24 and diverts most of the current to jumper cable 26 instead. Typically, as much as 99 percent of the current flows through jumper cable 26. As a result, there is negligible current induced in jumper cable 26 due to current flow in power line 24, and the power factor of the current and voltage sensed by circuitry 80 accurately reflects the power factor of the power transmission on power line 24. Without choke 81, the phase of the current through jumper cable 26 would depend on the current induced therein by the current flow through power line 24.

As illustrated in FIGS. 10 and 11, sensing circuitry 80 comprises an insulative sleeve 86 surrounding pipe 25, an electrical conductor 87 surrounding sleeve 86, an insulative layer 88 surrounding conductor 87, and an electrical conductor 89 surrounding insulative layer 88. A transformer comprising a laminated annular core 90 and a winding 92 surrounds conductor 89. Terminals 93 and 94 are connected to the ends of winding 92. A terminal 95 is connected to conductor 87. A terminal 96 is connected to conductor 89. As illustrated in FIG. 12, jumper 26 and conductor 87 form a capacitor 97 and conductors 87 and 89 form a capacitor 98. Capacitors 97 and 98 serve to step down the voltage between line 24 and ground.

The described embodiment of the invention is only considered to be preferred and illustrative of the inventive concept; the scope of the invention is not to be restricted to such embodiment. Various and numerous other arrangements may be devised by one skilled in the art without departing from the spirit and scope of the invention. For example, either a current sensor or a voltage sensor alone could be employed, or the sensor could take other forms than a transformer. Instead of hot line taps, the electrical connection to the power line could be made by two conventional aligned trunnion clamps mounted on the insulator.