Establishment of Capacitive Voltage Divider Method for the Calibration of Voltage Transformers

摘要

The objective is to render calibration service for the traceable measurements of the voltage ratio and phase angle between the primary and secondary voltages of the voltage transformers of any voltage ratio from 100V/100V to 100kV/100V at 50 Hz. This facility has been upgraded and established only recently after seeing the increasing demands of medium scale industries and utilities of power sector in India. The method employed makes use of CVD along with an EVD. This service for voltage transformers supports & provides a metrological back up for the bulk power energy metering upto 165kV/(3)~(1/2)/110V/(3)~(1/2). This ensures the uniformity of measurements which ultimately increases the confidence in the correct assessment of the quality & quantity of electric power produced, transmitted, distributed and consumed. At National Physical Laboratory of India, a VTTS is used to compare the Voltage Transformers used for revenue metering purposes against a capacitive voltage divider of accurately known uncertainties. For most practical purposes this role has been adequately met earlier by reference standard precision grade inductive voltage transformers and more recently by capacitive voltage divider. The statistical analysis of the calibration data assigns the uncertainties to the voltage transformers under calibration. For routine calibrations uncertainties of +- 60 ppm for ratio and +- 70 mu radians for phase angle are reported in the calibration certificates.