The Experts below are selected from a list of 318126 Experts worldwide ranked by ideXlab platform
Charles J. Mozina - One of the best experts on this subject based on the ideXlab platform.
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Improvements in protection and commissioning of digital transformer relays at medium voltage industrial facilities
IEEE Conference Record of Annual Pulp and Paper Industry Technical Conference, 2011Co-Authors: Charles J. MozinaAbstract:The application of multifunction digital relays to protect medium voltage power Transformers has become a common industrial practice. Industrial Transformers, unlike utility Transformers, frequently use neutral grounding resistors to limit ground current during faults to 200–400A range on medium voltage systems. This paper will discuss why these types of Transformers require sensitive ground differential protection. The paper will also discuss the basics of transformer protection including: phasing standards, through-fault withstand capability, differential/fusing/overcurrent protection, slope, CT requirements, harmonic restraint, and communicating these requirements properly when programming and commissioning new digital relays. The rationale for providing transformer overexcitation protection on all major Transformers within industrial facilities is also addressed. Advancements in digital technology have allowed relay manufacturers to include more and more relay functions within a single hardware platform as well as address more and more transformer winding configurations. This has resulted in digital transformer relays requiring an experienced protection engineer to set and an experienced relay testing technician to commission. Since there are fewer experienced professionals among us now, the next generation of transformer relays needs to concentrate on this complexity issue in addition to technical improvements. This paper addresses these issues that the author believes are the major shortcomings of existing digital transformer protective relays.
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improvements in protection and commissioning of digital transformer relays at medium voltage industrial facilities
Petroleum and Chemical Industry Technical Conference, 2010Co-Authors: Charles J. MozinaAbstract:The application of multifunction digital relays to protect medium voltage power Transformers has become a common industrial practice. Industrial Transformers, unlike utility Transformers, frequently use neutral grounding resistors to limit ground current during faults to 200–400A range on medium voltage systems. This paper will discuss why these types of Transformers require sensitive ground differential protection. The paper will also discuss the basics of transformer protection including: phasing standards, through-fault withstand capability, differential/fusing/overcurrent protection, slope, CT requirements, harmonic restraint, and communicating these requirements properly when programming and commissioning new digital relays. The rationale for providing transformer overexcitation protection on all major Transformers within industrial facilities is also addressed. Advancements in digital technology have allowed relay manufacturers to include more and more relay functions within a single hardware platform as well as address more and more transformer winding configurations. This has resulted in digital transformer relays requiring an Einstein to set and an Edison to commission. Since there are few Einstein's and Edison's among us, the next generation of transformer relays needs to concentrate on this complexity issue in addition to technical improvements. This paper addresses these issues that the author believes are the major shortcomings of existing digital transformer protective relays.
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protection and commissioning of multifunction digital transformer relays at medium voltage industrial facilities
Pulp and Paper Industry Conference, 2005Co-Authors: Charles J. MozinaAbstract:The application of multifunction digital relays to protect medium voltage power Transformers has become a common industrial practice. Industrial Transformers, unlike utility Transformers, frequently use neutral grounding resistors to limit ground current during faults to the 200-400-A level on medium voltage systems. This paper will discuss why these types of Transformers require sensitive ground differential protection. The paper will also discuss the basics of transformer protection including phasing standards, through-fault withstand capability, differential/fusing/overcurrent protection, slope, current transformer (CT) requirements, and harmonic restraint, and communicating these properly to new digital relays. The rationale for providing transformer overexcitation protection on all major Transformers within mill facilities is also addressed. Advancements in digital technology have allowed relay manufacturers to include more and more relay functions within a single hardware platform as well as address increasingly more transformer winding configurations. This has resulted in digital transformer relays requiring an Einstein to set and an Edison to commission. Since there are few Einsteins or Edisons among us, the next generation of transformer relays needs to concentrate on this complexity issue in addition to technical improvements. This paper addresses these issues that the author believes are the major shortcomings of existing digital transformer protective relays.
Johann Walter Kolar - One of the best experts on this subject based on the ideXlab platform.
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10kV SiC-based isolated DC-DC converter for medium voltage-connected Solid-State Transformers
Conference Proceedings - IEEE Applied Power Electronics Conference and Exposition - APEC, 2015Co-Authors: Daniel Rothmund, Th Guillod, G. Ortiz, Johann Walter KolarAbstract:Silicon-carbide semiconductor technology offers the possibility to synthesize power devices with unprecedented blocking voltage capabilities while achieving outstanding switching and conduction performances. Accordingly, this new semiconductor technology is especially interesting for Solid-State Transformer concepts and is utilized in this paper for designing a 25 kW/50 kHz prototype based on 10 kV SiC devices, featuring a 400V DC output. The focus is on the DC-DC converter stage while special attention is placed on the large step-down medium frequency transformer, whereby the impact of the rather high operating frequency and high number of turns with respect to the transformer's resonance frequency is analyzed This leads to useful scaling laws for the resonance frequency of Transformers in dependence of the operating frequency and construction parameters. Finally, a transformer prototype and efficiency and power density values for the DC-DC stage are presented.
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Self-capacitance of high-voltage Transformers
IEEE Transactions on Power Electronics, 2007Co-Authors: Luke Dalessandro, Fabiana Da Silveira Cavalcante, Johann Walter KolarAbstract:The calculation of a transformer's parasitics, such as its self capacitance, is fundamental for predicting the frequency behavior of the device, reducing this capacitance value and moreover for more advanced aims of capacitance integration and cancellation. This paper presents a comprehensive procedure for calculating all contributions to the self-capacitance of high-voltage Transformers and provides a detailed analysis of the problem, based on a physical approach. The advantages of the analytical formulation of the problem rather than a finite element method analysis are discussed. The approach and formulas presented in this paper can also be used for other wound components rather than just step-up Transformers. Finally, analytical and experimental results are presented for three different high-voltage transformer architectures.
W A A Salem - One of the best experts on this subject based on the ideXlab platform.
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predicting transformer temperature rise and loss of life in the presence of harmonic load currents
Ain Shams Engineering Journal, 2012Co-Authors: Osama E Gouda, Ghada M Amer, W A A SalemAbstract:Abstract Power Transformers represent the largest portion of capital investment in transmission and distribution substations. One of the most important parameters governing a transformer’s life expectancy is the hot spot temperature value. The aim of this paper is to introduce hot-spot and top-oil temperature model as top oil and hot spot temperature rise over ambient temperature model and thermal model under liner and non-linear loads. For more accurate temperature calculations, in this paper thermal dynamic model by MATLAB is used to calculate the power transformer temperature. The hot spot, top oil and loss life of power transformer under harmonics load are calculated. The measured temperatures of 25 MVA, 66/11 kV, ONAF cooling temperatures are compared with the suggested dynamic model.
Pasi Tallinen - One of the best experts on this subject based on the ideXlab platform.
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Protection of VSD Transformers
2017 Petroleum and Chemical Industry Conference Europe (PCIC Europe), 2017Co-Authors: Martin Bruha, Marcel Visser, Joseph Von Sebo, Esa Virtanen, Pasi TallinenAbstract:Variable Speed Drives (VSD) protect themselves as well as the driven motors. In contrast, the isolation input transformer typically requires its dedicated protection. Unlike distribution and power Transformers, the protection of VSD duty Transformers need to consider several additional aspects, such as non-sinusoidal current with harmonic content, multi-winding design, phase-shifted converter windings etc. This paper aims to explain the challenges related to protection of VSD Transformers. A guideline for reliable transformer protection based on good design practice is proposed. Finally the possibility to integrate the transformer protection into VSD protection scheme is being explored.
Pavlos S. Georgilakis - One of the best experts on this subject based on the ideXlab platform.
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A novel validated solution for lightning and surge protection of distribution Transformers
International Journal of Electrical Power & Energy Systems, 2014Co-Authors: Pavlos S. Georgilakis, Argyris G. KagiannasAbstract:This paper proposes an industrial solution (equipment) for lightning and surge protection of distribution Transformers. The proposed protection equipment has been installed at 100 distribution Transformers (sample) of the Public Power Corporation (PPC) of Greece. The article estimates the future transformer failures, considering two different cases: (a) transformer without the proposed protection system; and (b) transformer equipped with the proposed protection system. Three different methods are used to estimate the future transformer failures without the proposed protection system: Monte Carlo simulation, Poisson statistical distribution, and binomial statistical distribution. These three methods together with the c control chart method are also used in this paper, for the case of Transformers equipped with the proposed protection system, to estimate the maximum allowable number of yearly transformer failures in order the proposed protection system to be considered as an effective protection means. Moreover, the article computes the satisfactory sample size of Transformers in which the protection system has to be installed in order to be able to obtain statistically reliable results regarding the effectiveness of the proposed protection system. The results show that the proposed method is an excellent means for lightning and surge protection of distribution Transformers, since zero transformer failures have been observed so far during the whole period of its operation (29 months), in contrast with 8.36 average lightning and surge related failures per year in the same sample of 100 Transformers before the installation of the proposed protection equipment.
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Environmental Cost of Transformer Losses for Industrial and Commercial Users of Transformers
2011 North American Power Symposium, 2011Co-Authors: Pavlos S. Georgilakis, Juan C. Olivares-galvan, Rafael Escarela-perez, Issouf Fofana, George StefopoulosAbstract:Improvements in energy efficiency of electrical equipment reduce the greenhouse gas (GHG) emissions and contribute to the protection of the environment. This paper proposes a simplified model that quantifies the environmental cost of transformer losses and incorporates it into the economic evaluation of distribution Transformers for industrial and commercial users of Transformers. This environmental cost is coming from the cost to buy GHG emission credits because of the GHG emissions associated with supplying transformer losses throughout the transformer lifetime. Application results indicate that the environmental cost of transformer losses can reach on average 35% of transformer purchasing price for high-loss Transformers. That is why it is important to incorporate the environmental cost of transformer losses into the economic evaluation of distribution Transformers.
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Comparison of Three-Phase Distribution Transformer Banks Against Three-Phase Distribution Transformers
7th Mediterranean Conference and Exhibition on Power Generation Transmission Distribution and Energy Conversion (MedPower 2010), 2010Co-Authors: Juan C. Olivares-galvan, Ernesto Vázquez-martínez, Pavlos S. Georgilakis, Jesús A Mendieta-antúnezAbstract:This paper compares the mass and the total owning cost (TOC) of three-phase distribution transformer banks against three-phase distribution Transformers and the comparison is based on the minimum TOC. This is achieved through a field validated distribution transformer design program that automatically minimizes the objective function (TOC). Transformers compared in this paper are of shell-type, immersed in oil, and all are designed to meet the standard NMX-ANCE-2006-J116 in Mexico. The conclusion of this paper is that from the viewpoint of minimum mass and minimum TOC, in case of small-size Transformers (smaller than 45 kVA) it is recommended to use three-phase transformer banks, which is in disagreement with transformer textbooks. This result is due to the fact that more mass is needed for transformer tank, oil and high-voltage conductor for three-phase transformer in comparison to three-phase transformer bank. (6 pages)
