System for monitoring the insulation quality of step graded insulated high voltage apparatus
First Claim
1. An insulation monitoring system for measuring a charging current through an insulation system between a high voltage conductor and earth ground, said insulation monitoring system comprising:
- a. an AC current sensor for measuring said charging current and for converting said charging current to a first voltage signal proportional to said charging current;
b. a transmission network;
c. a transmitter coupled between said AC current sensor and said transmission network, said transmitter having electronic circuit means for converting said first voltage signal to a DC current and modulating a first current signal by said DC current for transmission over said transmission network, said modulated first current signal proportional to said charging current;
d. a controller for generating said first current signal and coupled to said transmitter by said transmission network to receive said modulated first current signal, said controller for demodulating said modulated first current signal to extract said DC current, converting said DC current to a voltage proportionally to said charging current, comparing said proportional voltage with a preset voltage level, and generating an alarm signal when said proportional voltage exceeds said preset voltage level; and
e. wherein said insulation monitoring system continuously monitors said insulation system.
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Accused Products
Abstract
A non-ferrous current sensor is used to continuously measure the charging current magnitude in step-graded foil and paper insulation systems used on high voltage measurement and control apparatus such as instrument transformers and on the condenser bushings of power transformers and circuit breakers. The low voltage measured signal is conditioned by an electronic circuit such that it modulates a DC signal in a system current control loop to provide continuous remote monitoring and alarm functions. Remote power is supplied to the sensor and conversion circuits through the current loop. Alarm level thresholds and alarm time delay are embodied in a control device which may be located in a remote location, away from the high voltage equipment. Step-graded insulation systems form a capacitively divided circuit between the high potential and ground. As the dielectric between the foil layers breaks down, the total capacitance of the insulation system increases, producing an increase in the charging current. The sensor detects changes in the charging current through the insulation ground conductor, indicating the degradation of the dielectric properties between the foil layers. Continuous monitoring of the alarm relay contacts provide a means for reporting abnormal conditions and initiating event-based maintenance procedures. The modulation of a standard 4-20 mA current control loop allows for a multiplicity of monitoring equipment to be added to the system for additional data collection and reporting.
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Citations
19 Claims
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1. An insulation monitoring system for measuring a charging current through an insulation system between a high voltage conductor and earth ground, said insulation monitoring system comprising:
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a. an AC current sensor for measuring said charging current and for converting said charging current to a first voltage signal proportional to said charging current; b. a transmission network; c. a transmitter coupled between said AC current sensor and said transmission network, said transmitter having electronic circuit means for converting said first voltage signal to a DC current and modulating a first current signal by said DC current for transmission over said transmission network, said modulated first current signal proportional to said charging current; d. a controller for generating said first current signal and coupled to said transmitter by said transmission network to receive said modulated first current signal, said controller for demodulating said modulated first current signal to extract said DC current, converting said DC current to a voltage proportionally to said charging current, comparing said proportional voltage with a preset voltage level, and generating an alarm signal when said proportional voltage exceeds said preset voltage level; and e. wherein said insulation monitoring system continuously monitors said insulation system. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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15. A method of monitoring insulation between a high voltage conductor and earth ground, said high voltage conductor and said earth ground comprising part of a high voltage system, said insulation monitoring method comprising:
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a. sensing a charging current between said high voltage conductor and said earth ground; b. converting said sensed charging current to a first voltage signal proportional to said charging current; c. rectifying said first voltage signal to a DC voltage; d. modulating a current loop with said DC voltage to produce a DC current signal proportional to said charging current for transmission to a remote location; e. demodulating said current loop at said remote location to extract said DC current signal; f. converting said DC, extracted current signal to a second voltage signal proportionally to said charging current; g. comparing said second voltage signal with a plurality of preset voltage levels, each of said plurality of preset levels representative of varying multiples of said charging current and having a predetermined alarm time delay period; and h. generating an alarm signal for each of said plurality of preset voltage levels when said second voltage signal exceeds said preset voltage level and said predetermined alarm time delay. - View Dependent Claims (16, 17, 18, 19)
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Specification