Abstract
The series summation method is an important method in the calibration of the voltage coefficient (VC) of the standard voltage transformers (VTs), in which the key step is connecting a fullyinsulated VT and a semi-insulated VT in series, and comparing them with the third VT under test. Caused by the imperfect electrical shielding of the serially-wound VTs, additional errors are introduced in the calibration. By analyzing the cause of the additional errors in the serial connection of the VTs, two methods were designed in this paper to measure the additional errors. The proposed methods were harnessed to measure the additional errors for a serial connection of a 35 kV fully-insulated two-stage voltage transformer (TSVT) and a 35 kV semi-insulated TSVT. The results show that the two methods give a consistency of better than 1.0 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> in ratio error and 2.0 μrad in phase displacement, respectively. The accurate measurement of the series additional errors and the correction of them significantly improve the accuracy of the VC measurement of a 110/√3 kV TSVT based on the series summation method. Furthermore, the VC measurement result is verified by the consistency of the series summation method with the series additional errors corrected and the high-voltage standard capacitor method.
Highlights
Electric energy trade and the loss measurement traceability of electric power transformers, reactors, etc. require a 10−6level accuracy and the traceability of power frequency high voltage ratio standards
THE ADDITIONAL ERRORS CAUSED BY THE VTS CONNECTED IN SERIES In the principle of the series summation method [7], the key step is the fully-insulated single-stage voltage transformers (SSVTs) and the semi-insulated SSVT connected in series, as shown in Fig. 1(a), where T1 is a semi-insulated SSVT, and T23 is a combined SSVT, which is composed of a fully-insulated voltage transformers (VTs) T2, and a high voltage isolation transformer (HVIT) with 1:1 ratio
The proposed methods were implemented in the additional errors measurement in the serial connection of a 35 kV fullyinsulated two-stage voltage transformer (TSVT) and a 35 kV semi-insulated TSVT, where the two methods gave an agreement of better than 1.0 × 10−6 in ratio error and 2.0 μrad in phase displacement respectively
Summary
Electric energy trade and the loss measurement traceability of electric power transformers, reactors, etc. require a 10−6level accuracy and the traceability of power frequency high voltage ratio standards. The summation method is another important method for calibrating VTs, which was proposed by scholars from PTB [3]–[6] This method was proposed for VT ratio traceability, which is the absolute determination of the errors of voltage transformers with parallel-series step-up method or with a summation method via intermediate transformers or capacitive divider. We implemented the proposed methods in the additional errors measurement in the serial connection of a 35 kV fully-insulated two-stage voltage transformer (TSVT) and a 35 kV semi-insulated TSVT. √ 110/ 3 kV two-stage voltage transformers with low-voltage excitation (LVE-TSVT) was measured with the series summation method presented in [7] with a replacement of SSVTs with TSVTs, including the additional errors in the serial connection are ignored or corrected. The results were compared with the HVSC method [2]
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