Multi-frequency validation algorithm for measurement and analysis of Dielectric Losses for Power and Distribution Transformers

Abstract

In this work, the authors focus on a highly-practical testing procedure bringing two main benefits to all power industry operators: a) higher confidence on the evaluation of dielectric testing, and; b) better utilization of technical and human resources. In the field, the application of dissipation factor measurements at (typically) 10 kV and at line-frequency (50 or 60 Hz) has been in use for many years without significant changes to the method. Nevertheless, multifrequency measurement of dielectric losses has opened a wider spectrum of analysis for power, distribution transformers and bushings. It is missing though, in the literature, a clear and properly supported discussion about how and when a single frequency measurement is validated with a multifrequency measurement or completely challenged. Important to recognize the link between line-frequency measurement, narrowband measurement (1 – 505 Hz) and full spectrum dielectric response (typically 1 kHz – 1 mHz). Limited information obtained in the frequency domain may identify a faulty unit but may not be used as a preventative test to minimize risk of failure. Preliminary research does address the need for limits of narrowband measurements. This is only possible when a correlation is established between temperature and frequency as it has been done using the well-known Arrhenius correlation. Therefore, in this work, the analysis of the dielectric response at frequencies beyond line-frequency leads to the undeniable benefit of using a multi-frequency dielectric loss procedure to establish higher confidence at the time to state not only technical but also financial decisions.