Patent Application
20240118318
This disclosure relates generally to a system and method for determining an open and closed position of a magnetically actuated switch and, more particularly, to a system and method for determining an open and closed position of a magnetically actuated vacuum interrupter that includes calculating the inductance of the magnetic actuator.
An electrical power distribution network, often referred to as an electrical grid, typically includes a number of power generation plants each having a number of power generators, such as gas turbines, nuclear reactors, coal-fired generators, hydro-electric dams, etc. The power plants provide power at a variety of medium voltages that are then stepped up by transformers to a high voltage AC signal to be connected to high voltage transmission lines that deliver electrical power to a number of substations typically located within a community, where the voltage is stepped down to a medium voltage for distribution. The substations provide the medium voltage power to a number of three-phase feeders including three single-phase feeder lines that carry the same current, but are 120° apart in phase. A number of three-phase and single phase lateral lines are tapped off of the feeder that provide the medium voltage to various distribution transformers, where the voltage is stepped down to a low voltage and is provided to a number of loads, such as homes, businesses, etc.
Some power distribution networks may employ a number of underground single-phase lateral circuits that feed residential and commercial customers. Often times these circuits are configured in a loop and fed from power sources at both ends, where an open circuit location in the loop isolates the two power sources. Transformers are dispersed along the loop that each service a number of loads, where the open circuit location is typically provided at one of the transformers. A single-phase line is coupled to the primary coil in each transformer so that current flows to the primary coils along the loop. It has been proposed in the art to provide a switching device at the source side and the load side of each transformer between the primary coil and the line. The two switching devices in each transformer can be controlled by a common control unit that provides fault isolation and power restoration in response to a fault in the line.
These, and other types of switching devices, often employ a vacuum interrupter and a magnetic actuator to operate the vacuum interrupter. A vacuum interrupter is a switch that employs opposing contacts, one fixed and one movable, positioned within a vacuum enclosure. When the vacuum interrupter is opened by operating the magnetic actuator to move the movable contact away from the fixed contact to prevent current flow through the interrupter a plasma arc is created between the contacts that is contained and quickly extinguished by the vacuum at the next zero current crossing.
The magnetic actuator used in these types of switching devices typically have an armature or plunger that is moved by an electrical winding wound on a stator to open and close the vacuum interrupter contacts, where the plunger and the stator provide a magnetic path for the magnetic flux produced by the winding, and where the plunger is rigidly fixed to the movable contact by a drive rod. In one design, when the actuator is controlled to close the vacuum interrupter, the winding is energized by current flow in one direction, which causes the plunger to move and seat against a latching plate. The current is then turned off to de-energize the coil and permanent magnets hold the plunger against the latching plate and against a compression force of an opening spring. When the actuator is controlled to open the vacuum interrupter, the winding is energized by current flow in the opposite direction, which breaks the latching force of the permanent magnets and allows the opening spring to open the vacuum interrupter. A compliance spring is provided in addition to the opening spring to provide an additional opening force at the beginning of the opening process so as to break the weld on the interrupter contacts.
Typically in these types of switching devices, a position indicator, such as a switch or an optical position indicator, is employed to show the position of the actuator to indicate if the vacuum interrupter is open or closed. However, the indicator must be positioned in the actuator with reasonably high tolerance to reliably indicate the vacuum interrupter position. In addition, wiring between the actuator position indicator and the controls is necessary and often needs to go through a number of connectors. These various things add cost to the switching device and provide a number of failure areas that can cause reliability problems.
The following discussion discloses and describes a system and method for determining an open and closed position of a magnetically actuated vacuum interrupter. The method includes applying a voltage signal of a known voltage to the actuator over a predetermined period and determining a change in current over time during the period when the voltage signal is applied to the actuator using an output of a Rogowski coil. The method also includes calculating the inductance using the voltage and the change in current over time at a predetermined time during the period and using the calculated inductance to determine whether the actuator and thus the vacuum interrupter are in the open or closed position.
Additional features of the disclosure will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings.
The following discussion of the embodiments of the disclosure directed to a system and method for determining an open and closed position of a magnetically actuated vacuum interrupter that includes calculating the inductance of the magnetic actuator is merely exemplary in nature, and is in no way intended to limit the disclosure or its applications or uses. For example, the system and method have particular application for use in a switching device associated with transformers in a residential loop circuit. However, the system and method may have other applications.
The switching device 10 also includes an actuator 40 that controls the drive rod 32 through a coupling rod 60 to open and close the vacuum interrupter 12. The actuator 40 includes an annular latching plate 42 having a central opening 44 through which the coupling rod 60 extends. The actuator 40 also includes a stator 46 defining a central opening 48, where a magnetic plunger 50 having a top shoulder 52 is slidably positioned within the opening 48. A coil 56 is positioned against the stator 46 in the opening 48 and a series of permanent magnets 58 are positioned between the plate 42 and the stator 46. A cup member 62 is rigidly secured to the plunger 50 and an opening spring 64 is provided within the cup member 62 and is positioned against the stator 46. A stop member 66 including an annular flange 68 is provided within the plunger 50 and is rigidly attached to the coupling rod 42 through the opening 44 in the plunger 50. A compliance spring 70 is provided within the cup member 62 and is positioned against the flange 68, which pushes the flange 68 against the shoulder 52.
The vacuum interrupter 12 and the actuator 40 are shown in the open position in
As will be discussed in detail below, this disclosure proposes that instead of using a switch or optical position sensor to indicate whether the actuator 40 is in the closed or open position, the inductance of the actuator 40 is calculated to determine the position of the actuator 40, which will be different for the open and closed positions. Both the open and closed position of the actuator 40 are stable and typically have a different magnetic path. Specifically, for the open position of the actuator 40 a large air gap is created in the magnetic path and for the closed position of the actuator 40 a small air gap is created in the magnetic path, which creates different inductances. Particularly, inductance L is a function of both the number of turns of the coil 56, and the magnetic path reluctance. When the magnetic path is different the inductance is different. It is known that V=L di/dt, and thus L=V/(di/dt). To obtain di/dt, the change in current can be measured over a certain time period. An alternative technique is to use a Rogowski coil, which measures di/dt directly. By measuring the coil drive voltage V and di/dt the inductance L can be calculated. This needs to be done without causing enough force to move the position of the actuator 40 in either the open or closed direction.
The Rogowski coil can be mounted directly to the control board (not shown) for the switching device 10 and additional circuitry and processing can be provided to calculate the inductance, as described.
The foregoing discussion discloses and describes merely exemplary embodiments of the present disclosure. One skilled in the art will readily recognize from such discussion and from the accompanying drawings and claims that various changes, modifications and variations can be made therein without departing from the spirit and scope of the disclosure as defined in the following claims.
This application claims the benefit of priority from the U.S. Provisional Application No. 63/415,188, filed on Oct. 11, 2022, the disclosure of which is hereby expressly incorporated herein by reference for all purposes.
| Number | Date | Country | |
|---|---|---|---|
| 63415188 | Oct 2022 | US |
