Demagnetization circuit for current transformers
First Claim
1. A system for measuring the residual flux in a current transformer, comprising:
- control circuit means generating a voltage waveform having two successive levels for reversing current flow in said current transformer, said control circuit means having a series resistance compensating circuit connected across the transformer winding and generating a stop signal to a processing unit upon detection of a predetermined current value flowing in said winding;
switching circuit means connected to said winding of said current transformer and producing an induction variation from the residual flux level up to saturation by successively switching the current when said voltage waveform is applied across the terminals of said winding; and
said processing unit receiving from said switching circuit means a first analog signal representative of said induction variation caused by said voltage waveform generated in a first time period and a second analog signal representative of the induction variation caused by said voltage waveform generated in a second time period, said unit determining saturation levels corresponding to a positive variation and to a negative variation of the induction in relation with said residual flux, and generating a signal representative of said current transformer residual flux.
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Accused Products
Abstract
The invention relates to a method and a system for measuring residual flux in current transformers. The system comprises a controlled circuit for generating two voltage levels for switching the current flow in the transformer. The switching circuit is connected to one current transformer winding and causes the induction to vary from the residual flux level to a saturation level through successive switching of the current when the voltage is applied across the winding terminals. A processing unit receives a first signal delivered by the switching circuit, such signal being representative of the induction variation for a time corresponding to the time period of the voltage. The processing unit further receives a signal representative of the induction variation caused by the application of the voltage for a second time period. The unit determines saturation levels corresponding to a positive variation and a negative variation of the induction as a function of the residual flux and generates a signal which corresponds to the residual flux of the current transformer.
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Citations
14 Claims
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1. A system for measuring the residual flux in a current transformer, comprising:
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control circuit means generating a voltage waveform having two successive levels for reversing current flow in said current transformer, said control circuit means having a series resistance compensating circuit connected across the transformer winding and generating a stop signal to a processing unit upon detection of a predetermined current value flowing in said winding; switching circuit means connected to said winding of said current transformer and producing an induction variation from the residual flux level up to saturation by successively switching the current when said voltage waveform is applied across the terminals of said winding; and said processing unit receiving from said switching circuit means a first analog signal representative of said induction variation caused by said voltage waveform generated in a first time period and a second analog signal representative of the induction variation caused by said voltage waveform generated in a second time period, said unit determining saturation levels corresponding to a positive variation and to a negative variation of the induction in relation with said residual flux, and generating a signal representative of said current transformer residual flux. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 12)
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11. A method for measuring the residual flux in a current transformer, comprising the steps of:
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generating a voltage waveform having two successive levels for reversing current flow in said current transformer; varying the induction level from a residual flux level up to saturation in one polarity and thereafter up to saturation in the other polarity by switching over said voltage waveform applied to a winding of said current transformer; determining, by means of a processing unit, a variation value of the induction caused by the voltage waveform issued in the first time period and an induction value caused by a voltage waveform issued in the second time period and summing up said induction values whereby to obtain a resultant analog signal representative of said residual flux in said transformer; said processing unit having a control circuit comprising a series resistance compensating circuit connected across the transformer winding, and generating a stop signal to a processing unit upon detection of a current value flowing in said winding. - View Dependent Claims (13, 14)
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Specification