The present invention relates generally to a load-tap changer position sensor. More particularly, the present invention is directed to a load-tap changer position sensor that uses magnetic reed switches to determine tap changer position and provides a useful and scaled analog output.
High voltage transformers are commonly used in power distribution networks. A tap changer is a device used in a transformer for regulation of the transformer output voltage within preset limits. Typically, the voltage regulation can be achieved by changing the ratio of the transformer by altering the number of turns in one winding of the transformer. An on-load tap position changer makes changes in tap position when the transformer is energized whereas as an off-load tap position changer makes changes in tap position when the transformer is de-energized. An on-load tap changer position sensor determines the position of the on-load tap changer so that various calculations associated with tap position can be performed with accurate tap position information.
On-load tap position sensors are typically coupled to the drive mechanism of the load tap changer and provide either an analog or digital output corresponding to the detected tap position. Generally, conventional on-load tap position sensors fall into one of three categories: resistor board position sensors, selsen indicators, or optical encoders.
Resistor board position sensors are the most common type of tap position sensor. These sensors use a resistor board that is mechanically coupled to the load tap changer drive mechanism. As the load tap changer is moved from tap to tap, a contact is moved from one contact to the next thereby changing the total resistance of the resistor circuit and providing a corresponding output. While generally accurate, the output of the resistor circuit can be significantly skewed if a copper oxide film develops on the surface of the resistor board.
Selsen indicators have a selsen motor which is directly coupled to the drive mechanism of the tap changer. The selsen motor includes a stator that receives an AC input voltage and a rotor having three conductors that are wired to a microprocessor. The phase angle of the AC signals from the three conductors provides tap changer position information to a microprocessor that decodes the signals to determine tap changer position. Selsen sensors offer the advantage of determining tap changer position in a non-contact manner, but disadvantageously require a microprocessor to decode the signals.
Another type of load tap changer position sensor is an optical encoder. Similar to selsen indicators, however, an optical encoder requires a processor to decode the output of the optical encoder.
The present invention is directed to a processor-free tap changer position sensor that uses magnetic reed switches. The use of magnetic reed switches resolves the issues associated with resistor board systems; namely, copper oxide deposits forming on the resistor board.
In one embodiment, the changer position sensor includes a series of radially spaced reed switches and a magnetic member that is rotated by a shaft that is coupled directly or indirectly to a load tap changer. As the position of the magnetic member changes, the location of the magnetic field created by the magnetic member moves. Each reed switch includes a set of contacts that close when in the presence of the magnetic field. The closed contacts create a voltage differential that is detected and used to determine the location of the closed reed switch and thus the position of the load tap changer.
It is therefore an object of the invention to provide a circuit of magnetically activated components to detect the position of a rotational magnetic member that is rotated in unison with a load tap changer to determine the position of the load tap changer.
Other objects, features, and advantages of the invention will become apparent to those skilled in the art from the following detailed description and accompanying drawings. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the present invention, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications.
This invention relates to a load tap changer position sensor, such as for use with an electrical transformer. As will be described more fully below, the load tap changer position sensor uses magnetic reed switches to indicate tap changer position thereby avoiding the drawbacks associated with resistor boards and other conventional changer position sensors.
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As noted above, the indicator wheel 46 carries a magnet 56. More particularly, the indicator wheel 46 includes an opening within which a small magnet 56 is positioned. The magnet 56 acts to create a magnetic field in the presence of a reed switch 58 of the circuit board 44 over which the magnet 56 is positioned. Thus, as the indicator wheel 46 is turned in response to the advancement of the gear 26, the magnet 56 housed within the indicator wheel 46 is moved over a corresponding one of the reed switches 58 of the circuit board 44. The resultant magnetic field created by the magnet 56 causes the contacts 60, 62 of the reed switch 58 directly below the magnet 56 to come together, thus completing the electrical path within the reed switch 58. The completion of the electrical path with the reed switch 58 causes an analog signal to be output to indicate the precise position of the load tap changer.
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Additionally, it is understood that the electrical circuit 66 may include additional components not shown or specifically described herein to enhance performance of the electrical circuit such as filters, voltage regulators, and the like. It is also recognized that the present invention may be embodied in electrical circuits different from that shown in
Accordingly, in one embodiment the present invention is directed to a method of determining the position of a load tap changer. The method includes detecting closing of a magnetically activated switch and then determining the position of that switch. More particularly, a magnetic indicator is rotated by shaft connected either directly or through a series of gears to the load tap changer. As that magnetic indicator is rotated, it creates a magnetic field of sufficient strength to close the contacts of a reed switch when in the magnetic field. Through a series of radially spaced reed switches, the position of the magnetic indicator and thus the load tap changer can be determined from the position of a closed reed switch.
Many changes and will modifications could be made to the invention without departing from the spirit thereof. The scope of these changes will become apparent from the appended claims.
This application claims the benefit of provisional application U.S. Ser. No. 60/826,860 filed Sep. 25, 2006, the disclosure of which is incorporated herein.
Number | Name | Date | Kind |
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3427530 | Hartwell et al. | Feb 1969 | A |
3811023 | Andersen | May 1974 | A |
4130789 | Neumann | Dec 1978 | A |
4567763 | Schiffbauer | Feb 1986 | A |
Number | Date | Country | |
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20080073189 A1 | Mar 2008 | US |
Number | Date | Country | |
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60826860 | Sep 2006 | US |