On-Line Evaluation of Voltage Transformer Accuracy

Abstract

The accuracy of voltage and current transformer (VT and CT) is a key factor in electric power metering. Ratio error and phase displacement calibration of VT and CT is traditionally carried out off-line. As a result of the expansion of the power grid and the increasing metering quality requirements from customer side, the off-line metering of VT and CT becomes more and more difficult. In this paper, a VT accuracy on-line evaluation system is developed, which can evaluate the accuracy of VT under on-line operating status. The principle and adopted key techniques in the development of the VT accuracy on-line evaluation system is introduced. Some on-site test results are also presented and analyzed as application demonstration.

An accurate on-site calibration system for electronic voltage transformers using a standard capacitor

“…However, in this case, EVTs do not operate in normal working conditions and the calibration results thus may not represent the actual accuracy class of the EVTs. (2) On-site calibration method [5,[9][10][11][12]. In this circumstance, a standard voltage transformer is connected to the HV line and the EVTs can be calibrated directly using the transformer.…”

“…The other issue is how to precisely obtain high-voltage signals under a complicated electromagnetic environment, such as one with input noise, frequency fluctuation, and harmonics. An on-line evaluation system has been realized using a reference capacitor divider [10], which can be connected to the power grid in the normal operational model. However, this system suffers the following problems: (i) the accuracy class of the system in question was only 0.1, and it therefore cannot calibrate EVTs with the desired 0.2 class accuracy; (ii) since the electronic circuit was directed to the capacitor divider, the electronic system may be sensitive to strong electromagnetic interferences in the case of overvoltage; (iii) the system is relatively bulky and inconvenient to utilize.…”