Abstract
This paper describes a comparison of overvoltage propagation in transformer windings. Expanding and evolving electrical networks comprise various classes of transient waveforms, related to network reconfigurations, failure stages and switching phenomena, including new sources based on power electronics devices. In particular, the integration of renewable energy sources—mainly solar and wind—as well as expanding charging and energy storage infrastructure for electric cars in smart cities results in network flexibility manifested by switching phenomena and transients propagation, both impulse and oscillating. Those external transients, having a magnitude below the applied protection level may have still a considerable effect on winding electrical insulation in transformers, mainly due to internal resonance phenomena, which have been the root cause of many transformer failures. Such cases might occur if the frequency content of the incoming waveform matches the resonance zones of the winding frequency characteristic. Due to this coincidence, the measurements were performed both in time and frequency domain, applying various classes of transients, representing impulse, chopped (time to chopping from 1 µs to 50 µs) and oscillating overvoltages. An additional novelty was a superposition of a full lighting impulse with an oscillating component in the form of a modulated wavelet. The comparison of propagation of those waveforms along the winding length as well as a transfer case between high and low voltage windings were analyzed. The presented mapping of overvoltage prone zones along the winding length can contribute to transformer design optimization, development of novel diagnostic methodology, improved protection concepts and the proper design of modern networks.
Highlights
Reliability of electric power systems, on both transmission and distribution levels, is an actual research topic [1,2,3,4,5,6,7,8,9,10,11,12]
The experiments were performed on a distribution transformer exposed during normal operational conditions to several surge stresses in the form of full and chopped lightning as well as switching phenomena
This paper reports about propagation of various waveforms of overvoltages inside transformer winding stressing the electric insulation system
Summary
Reliability of electric power systems, on both transmission and distribution levels, is an actual research topic [1,2,3,4,5,6,7,8,9,10,11,12]. According to the design principles, the peak values of transient overvoltages at transformer clamps are constrained by the installed protective devices to the level suggested by the insulation coordination [1,7,21,22] Those values are much higher than the maximum nominal voltage, the incoming transient containing the oscillating component below the protection level may form overvoltages inside the insulation system of high voltage equipment caused by internal resonance in the windings despite the applied surge arresters. Study on internal transient waveforms in transformers, subjected to standard and non-standard excitations, including superimposed waveforms containing oscillating components, are important for the development of more reliable transformers In this context, the mapping of overvoltage prone zones along the winding length can contribute to the development of proper diagnostic methodology, improved protection concepts and the proper design of modern networks
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
