Abstract
With the state’s high attention to clean energy and the requirement to reduce the loss of power grid transmission lines, DC UHV has developed rapidly in recent years. It refers to DC transmission and related technologies with voltage levels of ±800 kV (±750 kV) and above. In the power system, DC high-voltage transmission is inseparable from power equipment, but the higher the transmission voltage level, the higher the voltage of DC withstand voltage preventive test. Before the transmission of UHV DC transmission lines, if the DC voltage withstand device is 800 kV or above, the voltage withstand test shall not be carried out for the high-voltage line. The traditional direct comparison method using voltage divider cannot be used to measure the DC output voltage of DC UHV withstand voltage device on site. This paper analyzes the method of full coverage of DC UHV system in limited voltage range and the method of out of range calibration using scale factor. In order to solve the problem of voltage traceability in the DC high voltage generator, especially the voltage traceability of the field DC UHV device, when the voltage output range of the calibrated DC high voltage generator exceeds the measurement range of the standard, the standard value of the voltage calibration point beyond the range can be determined by comparison and obtained through the linearity test. The comparison with the standard shall be conducted at a voltage not lower than 20% of the rated voltage of the calibrated DC high voltage generator, and compared to the maximum voltage of the standard voltage divider. The comparison is carried out at a (a ≥ 2) voltage point. When comparing at a point, the highest voltage level is equal to the upper limit of the standard. Under a voltage point, according to the mathematical relationship between the voltage standard value of the tested device and the current flowing through the linear load resistance, the fitting function can be obtained through the linear regression method. For b (b ≥ 4) calibration points beyond the measurement range of DC standard voltage divider, the standard value can be “extrapolated” from the linear load resistance current and the fitting function Yang (2002). Through comparison and verification, the method is feasible, which is of great significance to promote the compilation of calibration specification for DC high voltage generator.
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