Propagation of Overvoltages in the Form of Impulse, Chopped and Oscillating Waveforms in Transformer Windings—Time and Frequency Domain Approach

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.

Effect of shield placement for transient voltage mitigation due to switching surges in a 33/11 kV transformer windings

“…However, the variations in the transient voltages are not observed at the end of discs 93, 83 and 73 as compared to disc 96 from 0 μs to 500 μs. It should be noted that the amplitude of the OSI depends on the type of an electrical equivalent circuit and time of the oscillating components in the transient voltage [ 16 ].…”

“…Transformer winding equivalent circuits are traditionally used to examine the voltage surge distribution in the transformer windings [7][8][9]. Several studies have been carried out to examine the transient voltage surge propagations through simulations and experimental setups [10][11][12][13][14][15][16]. Lumped equivalent circuit model have been widely used to analyze the resonant responses of windings subjected to switching surges [6,[17][18][19][20].…”

Transformation of Transient Overvoltages by Inductive Voltage Transformers

“…In accordance with the standard IEC 60071-1, transient overvoltages may be divided into three types: slow-front, fast-front and very fast-front [ 1 , 2 ]. It applies to three-phase AC systems having a highest voltage for equipment above 1 kV.…”

Evaluation of Filtered Spark Gap on the Lightning Protection of Distribution Transformers: Experimental and Simulation Study

“…However, among the electrical equipment, transformers are considered as one of the most expensive equipment in the power system. The unexpected external transients, even those with magnitude lower than the applied protection level, may severely stress the winding insulation in transformers [9]. To this end, in the literature, there exist many works that focused on investigating different methods to enhance the protection level of transformers against lightning overvoltages.…”