A Simple Method for the Calibration of Traditional and Electronic Measurement Current and Voltage Transformers

The calibration of measurement transformers represents a classical task in the practice of electrical measurements. The great part of the commercial instruments expressly designed for this purpose founds their working principle on a scheme based on an idea of Kusters and Moore. Though they can assure a very high accuracy, the need to employ a high-performance electromagnetic circuit makes them very expensive and usually not suitable for measurements at frequencies higher than 50 or 60 Hz. For this reason, this kind of instruments cannot be employed for calibration of the new generation of current and voltage transducers, like electronic measurement transformers, which employment is growing in all the applications where wide bandwidth is required. In this paper a new method for the calibration both of electromagnetic voltage and current measurement transformers (VT and CT) and electronic voltage and current measurement transformers (EVT and ECT) is discussed and a deep metrological characterization is carried out. The novelty of the proposed method is represented by a completely different approach to the measurement of the ratio and phase errors of the measurement transformers. The method is based on proper digital signal processing of the signals collected at the secondaries of the transformer under test and of a reference transformer, when the same signal is applied to their primary. Since no auxiliary electromagnetic circuits are required, this solution can be easily implemented, in a simple and cost-effective way. In spite of its simplicity, the tests developed on a prototype clearly point out that the proposed system is suitable for the calibration of measurement transformers with precision class up to 0.1 in the frequency range from 50 Hz to 1 kHz.