Load voltage based tap changer monitoring system
First Claim
1. A transformer having a selectable winding ratio comprising:
- at least one load terminal;
a plurality of windings including a tap assembly which is positionable to incrementally change the winding ratio of the transformer to vary the voltage at the load terminal;
an electric drive mechanically coupled to the tap assembly to selectively position the tap assembly to effect incremental changes of the winding ratio;
a count signal generator coupled to the tap assembly to generate a count signal in response to a tap change;
a monitoring circuit coupled to the load terminal to produce a load voltage signal representative of the load voltage at the load terminal; and
a digital processing circuit including an input port coupled to the monitoring circuit and count signal generator, and an output port coupled to the electric drive, the processing circuit being configured to periodically sample the load voltage signal applied to the input port, compare a first load voltage value sampled at a first time with a pre-defined load set value, apply control signals to the output port to activate the electric drive if the difference between the first and second voltage values exceeds a predetermined limit, compare a third load voltage value sampled at a third time prior to a count signal with a fourth load voltage value sampled at a time subsequent to the count signal, determine the direction of tap change based upon the comparison of the third and fourth load voltage values, and determine a new tap position value based upon the direction of tap change.
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Accused Products
Abstract
A tap changer including a tap positionable to vary the winding ratio of the transformer in response to changes in an electric load on the transformer is disclosed herein. The transformer includes an electric drive which is electrically powered to selectively position the tap to effect incremental changes of the winding ratio. The transformer includes a monitoring system which monitors the load voltage of the transformer with at least one potential transformer which produces signals which are converted to digital data values stored in a circular data buffer. Each time control signals are applied to the electric drive and a subsequent tap change indication is detected, the first and last data values in the circular buffer are compared, and when the difference between the values exceeds a predetermine limit, the system updates a tap position value which represents the position of the tap.
36 Citations
18 Claims
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1. A transformer having a selectable winding ratio comprising:
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at least one load terminal; a plurality of windings including a tap assembly which is positionable to incrementally change the winding ratio of the transformer to vary the voltage at the load terminal; an electric drive mechanically coupled to the tap assembly to selectively position the tap assembly to effect incremental changes of the winding ratio; a count signal generator coupled to the tap assembly to generate a count signal in response to a tap change; a monitoring circuit coupled to the load terminal to produce a load voltage signal representative of the load voltage at the load terminal; and a digital processing circuit including an input port coupled to the monitoring circuit and count signal generator, and an output port coupled to the electric drive, the processing circuit being configured to periodically sample the load voltage signal applied to the input port, compare a first load voltage value sampled at a first time with a pre-defined load set value, apply control signals to the output port to activate the electric drive if the difference between the first and second voltage values exceeds a predetermined limit, compare a third load voltage value sampled at a third time prior to a count signal with a fourth load voltage value sampled at a time subsequent to the count signal, determine the direction of tap change based upon the comparison of the third and fourth load voltage values, and determine a new tap position value based upon the direction of tap change. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A transformer having a selectable winding ratio comprising:
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at least one load terminal; a plurality of windings including a tap assembly which is positionable to incrementally change the winding ratio of the transformer to vary the voltage at the load terminal; drive means for selectively positioning the tap assembly in response to control signals to effect incremental changes of the winding ratio; count means for generating count signal in response to a tap change; monitoring means for producing a load voltage signal representative of the load voltage at the load terminal; and processing means for periodically sampling the load voltage signal and count signal to generate digital data values representative thereof, comparing first data representative of the load voltage signal sampled at a first time with second data representative of a pre-defined load set value, applying control signals to the drive means to activate the drive means if the difference between the first and second data exceeds a predetermined limit, comparing third data representative of the load voltage signal sampled at a third time prior to a count signal with fourth data representative of load voltage signals sampled at a time subsequent to the count signal, determining the direction of tap change based upon the comparison of the third and fourth data, and determining a new tap position value based upon the direction of tap change. - View Dependent Claims (10, 11, 12, 13, 14, 15)
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16. In a transformer of the type having a selectable winding ratio, a plurality of windings including a tap assembly which is positionable to incrementally change the winding ratio of the transformer to change load voltage at a load terminal of the transformer, and an electric drive mechanically coupled to the tap assembly to selectively position the tap assembly to effect incremental changes of the winding ratio, a method comprising the steps of:
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monitoring the load terminal to generate a load voltage signal representative of the load voltage at the load terminal; periodically sampling the load voltage signal to generate a plurality of digital data values representative of the load voltage signals; applying power to the electric drive to selectively position the tap assembly to effect incremental changes of the winding ratio; comparing first data representative of the load voltage signal sampled at a first time prior to a count signal with second data representative of a pre-defined load set value; comparing third data representative of the load voltage value sampled at a third time prior to a count signal to a fourth data representative of a fourth load voltage value sampled at a time subsequent to the count signal; determining the direction of tap change based upon the comparison of the third and fourth data; and determining a new tap position value based upon the direction of tap change. - View Dependent Claims (17, 18)
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Specification