The subject matter described herein generally relates to electromagnetic sensor coils and, in particular, to a disassociated split electrical current sensor coil adapted for installation over live power distribution lines in an AC electrical power grid.
Electrical current sensors are frequently installed on electrical transmission or distribution lines in regional electrical power grids in order to support power line monitoring and power management activities. The sensors are typically installed upon a transmission or distribution line and combined with a remote terminal unit (RTU) or similar communications device in order to report current flow to a monitoring station run by the grid operator. The sensed current flow or line dynamics, along with other sensed information such as line voltage, frequency, temperature, and the like, are used by the grid operator to configure and manage the network of transmission lines that interconnects remote electrical generation stations with local power distribution substations. Similar electrical current sensors are also incorporated into protective relay circuits that safeguard high value electromechnical equipment, such as arc furnaces, motors, and generators and identify electrical faults. The sensors are typically installed during connection of the equipment to an on-site transformer and/or busbar connections to local power distribution lines, or during later investigations of such connections in response to an electrical fault. The sensed current flow is used to actuate a relay to break the equipment power circuit if there is an overcurrent condition (indicating, for example, a potential short circuit) or, in some circuits, an undercurrent condition (indicating some other form of equipment fault).
In AC systems, these electrical current sensors have typically been designed as current transformers (CTs). In a CT, an alternating current flowing through a primary winding or coil induces current to flow through a secondary winding or coil due to its time-varying magnetic flux. A magnetic core, such as a ferrite or silicon steel core, serves as the winding core or is otherwise positioned within the coils in order to concentrate the magnetic flux and enhance the output power of the secondary coil, which may be used to operate a device such as a protective relay. Recently, some electrical current sensors have been designed as Rogowski coils. In a Rogowski coil, a single winding around an approximately toroidal, non-magnetic core serves as the sensor element. An alternating current flowing through the annular void at the center of the toroid induces current to flow through the Rogowski coil due to its time-varying magnetic flux. Although the Rogowski coil is not able to generate an output power similar to a CT, and consequently must be combined with powered electronics in order to communicate with remote monitoring stations or to operate a relay, the Rogowski coil can effectively reject the influence of external time-varying magnetic fields, sensing only the alternating current carried within power lines routed through the coil's annular void. Thus, Rogowski coils are preferred for use in grid monitoring applications where a monitored transmission or distribution line is likely to be positioned in close proximity to other such lines which might potentially contaminate sensor measurements.
The ability of a Rogowski coil to reject the influence of external time-varying magnetic fields depends upon the uniformity and regularity of the spacing of the coil elements. Although a Rogowski coil does not require a closed toroid, the discontinuity between the ends of the coil presents a potential source of irregularity in the windings and susceptibility to the influence of such external fields. In addition, when a Rogowski coil is to be installed over a live power line, the coil must be flexed or distorted at least at one other point in order to open the ends of the coil and allow the power line to pass through the discontinuity. These sources of difficulty have generally prevented Rogowski coils from being retrofit over live power distribution lines. In contrast to power transmission lines, where individual lines can be taken out of service due to the redundancy and overcapacity designed into regional transmission grids, and protective relay circuits, where specific equipment can be scheduled out of service for upgrade or maintenance, power distribution lines lack redundancy and can serve hundreds or even thousands of separate end-users, including both commercial and residential consumers. Thus, there is a need for a Rogowski-like electrical current sensor which can easily be installed over a live power distribution line, preferably from the ground or from the bucket of a lift truck. In addition, it would be advantageous if the electrical current sensor did not require fine manipulation of its constituent parts or direct manipulation by lineworkers equipped with insulating gloves.
Presented is a disassociated split sensor coil and method of manufacturing which produces, in effect, a disassociated split Rogowski coil. The disassociated split sensor coil is suitable for installation over live power distribution lines, such as in retrofit installations of “smart grid” distribution line sensors, and adapted for mounting within a clamshell sensor housing that can be manipulated by a lineworker equipped with a conventional “hot stick” or live line tool. Further objects and advantages of the disclosed coil and method will be apparent from the detailed discussion provided below.
In a first aspect, the disassociated split sensor coil comprises first and second non-magnetic, hemi-toroidal cores. The first and second cores each include a surface channel extending from one end of the hemi-toroidal core to the opposite end of the hemi-toroidal core. A first wire section is wound about the first core to form a first helical coil extending from the one end to the opposite end, with the first helical coil being electrically connected to a first terminal wire proximate the one end and to a first connecting wire proximate the opposite end. The first connecting wire is disposed so as to extend through the surface channel of the first core, under the first helical coil, from the opposite end to at least the first end. A second wire section is wound about the second core to form a second helical coil extending from the one end to the opposite end, with the second helical coil being electrically connected to a second terminal wire proximate the one end and to a second connecting wire proximate the opposite end. The second connecting wire is disposed so as to extend through the surface channel of the second core, under the second helical coil, from the opposite end to at least first end. The first connecting wire and the second connecting wire are electrically connected to each other to form a continuous electrical path from the first terminal wire to the second terminal wire, with the first and second terminal wires being electrically connectable to a monitoring circuit.
In a second aspect, a method of manufacturing a disassociated split sensor coil comprises the steps of (a) obtaining a non-magnetic, hemi-toroidal core having a surface channel extending from one end of the hemi-toroidal core to the opposite end of the hemi-toroidal core, (b) placing a first length of a wire within the surface channel so as to extend from at least the one end to at least the opposite end, (c) winding a second length of the wire about the hemi-toroidal core to form a helical coil section extending from the opposite end to the one end, and (d) providing a third length of the wire extending from the one end, wherein the first, second, and third lengths are sequentially ordered lengths of a contiguous wire. The steps are repeated to form a pair of disassociated split sensor coil elements, with the elements being electrically connectable by joining the first lengths of wire to form the disassociated split sensor coil. Preferably, the first length of wire includes a loop portion disposed between the opposite end of the hemi-toroidal core and the helical coil section, with the first length being drawn out of the surface channel at the one end to draw the loop portion taught at the opposite end of the hemi-toroidal core after the winding of the second length of the wire.
Several additional features, functions, and advantages can be achieved in various embodiments, examples of which can be seen with reference to the following description and drawings.
The accompanying figures depict various embodiments of the split sensor coil and manufacturing method. A brief description of each figure is provided below.
With initial reference to
Turning to
In an exemplary embodiment, shown in
In further exemplary embodiments, shown in
As shown in
Various methods may be employed to manufacture the split sensor coil 100. In some embodiments, a method 400 of manufacturing includes the steps of: obtaining a non-magnetic, hemi-toroidal core 110 having a surface channel 120 extending from one end, 130, of the hemi-toroidal core to the opposite end, 140, of the hemi-toroidal core, 410; placing a first length 170 of a wire within the surface channel 120 so as to extend from at least the one end 130 to at least the opposite end 140, 420; winding a second length 150 of the wire about the hemi-toroidal core to form a helical coil section 152 extending from the opposite end 140 to the one end 130, 430; and providing a third length 160 of the wire extending from the one end 130, 440. The winding of the second length 150 of wire may be performed manually, but is preferably performed by a coil winding machine. As indicated above, the hemi-toroidal core 110 may include a flange 132 disposed at the one end and a flange 142 disposed at the opposite end, whereupon the flange 142 may be used to register a start location with the coil winding machine and the flange 132 may be used to register a stop location with the coil winding machine. To ease manufacturing using a coil winding machine, the first length 170 of wire may include a loop portion 172 disposed between the opposite end 140 of the hemi-toroidal core 110 and the start of the helical coil section 152. The loop portion 172 allows for manipulation of the wire into position within the coil winding machine, easing the winding process. After winding of the helical coil section 152, the method may include the step of drawing the first length 170 of wire out of the surface channel 120 through the one end 130, causing the loop portion 172 to be drawn taught at the opposite end 140, 432—most specifically, against the hook element 146 within notch 144. This step 432 both advantageously secures the loop portion 170 at the opposite end 140 and yields a device having a helical coil section 152, terminal wire 160, and connecting wire 170 of consistent length (as measured from the one end 130 or any other consistently applied baseline, such a predetermined lead length) formed from a single contiguous wire.
The method 400 of manufacturing may further include the step of embedding at least the helical coil section 152 within an overmold portion 210, 450. Prefereably, the step 450 embeds all the helical coil section 152, flange 132 and flange 142 within the overmold portion 210. More preferably, the step 450 forms a flange 232 on one end 230 of the overmold portion 210 and a flange 242 on the opposite end 240 of the overmold portion. Most preferably, the flanges 232, 242 of the overmold portion are formed at and over the flanges 132, 142 of the hemi-toroidal core 110. Although flanges like the flanges 232, 242 may be formed elsewhere on the overmold, flanges provided in this position advantageously provide the greatest control over the geometry and width of the discontinuities between the sensor coils 152.
The steps 410 through 440 or 450 are repeated to form a pair of disassociated split sensor coil elements, with the elements being electrically connectable as described earlier. The method may further include the step of positioning the disassociated split sensor coil 100 within a sensor housing, e.g., clamshell sensor housing 300, such that the one ends 130 are mechanically disposable in a mutually opposing and abutting relationship and the opposite ends 140 are mechanically disposable in a mutually opposing and abutting relationship. However, it will be recognized that such a step is more strictly a configuration step than a manufacturing step. The reader will also recognize that the term “abutting relationship” is intended to encompass circumstances in which a the ends 130, 140 of the hemi-toroidal cores 110 are components of the ends 230, 240 of overmold portions 210, such that a thin layer of overmold material, e.g., 0.02 inches may be interposed between the respective ends.
The embodiments of the invention shown in the drawings and described above are exemplary of numerous embodiments that may be made within the scope of the appended claims. It is contemplated that numerous other configurations recombining individual features or elements of the disclosed embodiments may be created by taking advantage of the disclosure as a whole. It is the applicant's intention that the scope of the patent issuing herefrom will be limited only by the scope of the appended claims.
What is claimed is: