SYSTEM FOR MONITORING THE INSULATION QUALITY OF STEP GRADED INSULATED HIGH VOLTAGE APPARATUS

摘要

A non-ferrous current sensor is used to continuouslymeasure the charging current magnitude in step-graded foil andpaper insulation systems used on high voltage measurement andcontrol apparatus such as instrument transformers and on thecondenser bushings of power transformers and circuit breakers.The low voltage measured signal is conditioned by an electroniccircuit such that it modulates a DC signal in a system currentcontrol loop to provide continuous remote monitoring and alarmfunctions. Remote power is supplied to the sensor andconversion circuits through the current loop. Alarm levelthresholds and alarm time delay are embodied in a control devicewhich may be located in a remote location, away from the highvoltage equipment. Step-graded insulation systems form acapacitively divided circuit between the high potential andground. 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 detectschanges in the charging current through the insulation groundconductor, indicating the degradation of the dielectric propertiesbetween the foil layers. Continuous monitoring of the alarmrelay contacts provide a means for reporting abnormal conditionsand initiating event-based maintenance procedures. Themodulation of a standard 4-20 mA current control loop allowsfor a multiplicity of monitoring equipment to be added to thesystem for additional data collection and reporting.