Electromagnetic voltage transformers play a critical role in the metering systems of power plants and substations. Their measurement accuracy directly affects the interests of power generation, transmission, and distribution. To ensure reliability, it is essential to periodically verify these transformers using dedicated voltage transformer testers. However, as voltage levels increase—especially when the primary voltage exceeds 110 kV—the weight and complexity of traditional verification equipment like voltage regulators, boosters, and standard transformers grow exponentially. This makes on-site verification increasingly challenging and less efficient.

In response to these challenges, the Shanxi Machinery Research Institute introduced an innovative approach in the 1980s. They proposed a method for calculating high-voltage transformer errors based on the error at a low-voltage reference point and the variation curve of the primary excitation current. This technique, known as the "low-to-high" method, offers a more practical solution for high-voltage verification without requiring heavy and cumbersome equipment.

Although low-level high-voltage transformer field calibrators have gained widespread use in substation and transformer testing environments, there is still no official national calibration specification for such devices. This lack of standardized procedures has hindered their broader adoption and trust in their measurement results. Therefore, developing a reliable calibration method is crucial to ensure the accuracy and traceability of these instruments.

One common calibration method currently used in China is the indirect comparison approach. This involves using a low-level high-voltage field calibrator alongside a conventional voltage transformer differential pressure device. By following the wiring diagrams shown in Figure 1 and Figure 2, both devices are used to calibrate the same PT (the reference sample). The difference between the two readings is taken as the final result. However, due to variations in accuracy levels, compensation types, stability, and load conditions among different samples, achieving consistent calibration results across laboratories remains a challenge.

To address this, further research and standardization efforts are needed to improve the consistency and reliability of field calibrator measurements. This will not only enhance the performance of these instruments but also support safer and more accurate electrical system operations in the future.

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