Core Structure and its Association with Transformer Susceptibility towards Ferroresonance (original) (raw)
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Ferroresonance and its implications on transformers and power systems
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Ferroresonance in Three-Phase Power Distribution Transformers: Sources, Consequences and Prevention
Ferroresonance is a phenomenon that involves high distorted levels of overvoltage and overcurrents. During the last decades, the three-phase ferroresonance research has suffered several changes due to the continuously changing equipment and network. This paper analyses every main factor that is somehow related with the origin, consequences and the preventive decisions that may lead us to avoid the three-phase ferroresonance to appear. Besides this, it gives the opportunity to get a quick identification of such a complex phenomenon.
2017
Evaluation of risk of ferroresonance in voltage transformers is typically performed by transient simulations using non-linear models of instrument transformers. In the process of selection and optimization of mitigating and damping approach the experimental verification is always required at the final stage. Such experiments performed on full-scale devices are complex, costly and hazardous, as the ferroresonance in VTs is associated with a risk of a ground-fault. In the present paper an experimental set-up is presented, allowing one to perform studies of ferroresonance in a safe, low voltage environment. The set-up comprises a separating transformer providing an ungrounded 3-phase LV network supply. Ferroresonant conditions were investigated for variable network capacitance taking into account capacitance values scaling to the LV network level. Both in the simulations and in the experiments the ferroresonant oscillations were initiated by an intermittent single-phase earth-fault. Us...
Laboratory ferroresonance measurements in power transformers
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2019
As we know that one of the most important equipment in power system, transformer plays a major role for stable operation of the power system. The transformer working under high and medium voltage network influences various stresses under working condition. As the ageing processes or minor faults on the transformer can cause the core deformation which leads to change the mechanical and electrical properties of the transformer. Sweep frequency response analysis (SFRA) is used as a tool for detection of core deformation or mechanical deterioration in transformer which is due to large electromechanical forces occurring from the fault currents or due to transportation and relocation of transformer. In this method, the frequency responses of a transformer is taken both at manufacturing industry and concern site. Then both the response is compared to predict the fault taken place in active part. But in old aged transformer, this response is not possible. So Cross Correlation Co-Efficient (...
FE-based application for the evaluation of core-losses in distribution transformers
Proceedings of the 23rd International Conference on Electrical Machines ICEM 2018, Alexandroupoli, Greece, September 3-6, 2018
This paper describes a finite–element (FE) based application for the numerical evaluation of core–losses in distribution transformer. The specific application is centered around a method that permits the generation of software applications for a variety of user/customer defined problems and makes use of the FE method in order to solve them. A variety of problems are considered such as electromagnetic or thermal, steady state or transient, linear or non–linear, and two– dimensional (2–D) or three–dimensional (3–D). The present manuscript focuses on one such application and more specifically on the problem of core–losses evaluation in oil– immersed, wound core, distribution transformers, both single– phase and three–phase. Finally, the core–losses of a single–phase wound core transformer are computed using the " CORELOSS " application and they are compared with results obtained with a commercial FE package.
IEEE Transactions on Energy Conversion, 2011
This paper investigates the stability domain of ferroresonance in asymmetric three-phase three-leg transformers considering magnetic couplings and hysteresis effects of the core. A newly developed and accurate time-domain transformer model capable of simulating dynamic and transient operating conditions is implemented in this study. The model is based on electromagnetic circuit theory and considers dynamic hysteresis effects (major and minor loops) as well as core topology, asymmetry, and magnetic flux cross-coupling interactions of the core legs. Unbalanced switching with series and shunt capacitances, which is known to increase the risk of ferroresonance, is studied with the developed model. The validity of the model under ferroresonant conditions is confirmed by comparisons with extensive experimental data. The main contribution is a new analysis of (a)symmetric three-phase transformer ferroresonance behavior with an accurate core model capable of predicting ferroresonance modes. Index Terms-Ferroresonance, hysteresis, nonlinear and threephase transformer model. I. INTRODUCTION M ANY investigations of ferroresonance phenomena in power and instrument transformers have been performed, spanning nearly a century of accumulated research [1], [2]. Much progress has been made in the modeling and understanding of single-phase transformer ferroresonance. However, one of the weakest areas in ferroresonance research remains in the modeling of (a)symmetric three-phase transformers.
2016
By identifying the characteristic equation of the specific no-load losses of each iron sheet based on the core configuration, it is possible to reach a high level of accuracy in detecting no-load losses over a wide range of flux density. The method is applicable and frequently used for reference as well as for new sheet types that appear on the market. The results presented in this paper are based on one year experience, showing that the total weight and volume of transformers have clearly been reduced