Measurement Procedure to Investigate Ageing of Low-Power Voltage Transformers

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The power network is experiencing a huge replacement of equipment. The legacy instrument transformers (ITs) are being substituted, at all voltage levels, with the new generation of low-power instrument transformers (LPITs). They feature various benefits compared to the previous generation. For example, they are smaller, they are easier to install, they have larger bandwidths, etc. compared to ITs. However, the recent introduction of LPITs results in a lack of information about several aspects concerning their behavior. For instance, there is almost no literature (or standard) dealing with the ageing of either current or voltage LPITs (LPCTs and LPVTs, respectively). Nevertheless, considering that once installed LPITs are rarely calibrated again before decades, information on their ageing is crucial. To this purpose, this work introduces a new test to investigate the ageing of LPITs. Furthermore, measurement procedures are described to evaluate the effect of ageing on their accuracy. Both the test and the measurement procedures are then experimentally validated on two off-the-shelf resistive LPVTs. From the results several conclusions can be drawn. First, the designed test is easy to implement and not expensive. Second, the accuracy of the device under test is clearly affected by the designed test. Third, the measurement procedure allows to estimate the thermal constant of a device and its in-field behavior.