Innovative solutions for distribution transformer cores and windings

Focusing on the real needs of the transformer core manufacturing process, the first step is to improve existing solutions and find new, innovative solutions at a whole process level, with the aim to produce highly efficient transformer cores in a both productive and competitive way. The first innovative improvement concerns the automation of the stacking process, so far operated only manually, which can now be included in line with the core cutting process, thus responding to one of the major manufacturing issues: the productivity. The second innovation refers to the automation of the lamination replacement into the cutting machine, thus drastically reducing the average time for this operation from current approximately 10 mins to only 15 seconds, with significant improvement of the productivity, especially with different lamination widths. The third major innovation concerns the core-filling factor of the distribution transformer. The current compromise between optimized shape and a minimum number of different widths of lamination, results in a core-filling factor ranging from 94 % to 96 %, using in general 7 to 11 different widths. Our revolutionary solution implies the use of octagonal shaped cores to reach a 99 % filling factor, with a significant saving on materials, and a correspondent improvement of no load losses (core losses), due to the extra 4-6 % of increased material. This process patented (patent no. 102017000022419 [1]) under the name of TWINCORE exploits the optimized results from the unification of core cutting and stacking implemented by an inline slitting head, covering the entire production process with only 2 different sizes of mother rolls and using a single automated machine, thus avoiding intermediate storages and reducing lamination scrap. Finally, the article will explore the optimization of the windings, resulting in a complete optimisation of the transformer’s most crucial components

Innovative solutions for distribution transformer cores and windings

Focusing on the real needs of the transformer core manufacturing process, the first step is to improve existing solutions and find new, innovative solutions at a whole process level, with the aim to produce highly efficient transformer cores in a both productive and competitive way. The first innovative improvement concerns the automation of the stacking process, so far operated only manually, which can now be included in line with the core cutting process, thus responding to one of the major manufacturing issues: the productivity. The second innovation refers to the automation of the lamination replacement into the cutting machine, thus drastically reducing the average time for this operation from current approximately 10 mins to only 15 seconds, with significant improvement of the productivity, especially with different lamination widths. The third major innovation concerns the core-filling factor of the distribution transformer. The current compromise between optimized shape and a minimum number of different widths of lamination, results in a core-filling factor ranging from 94 % to 96 %, using in general 7 to 11 different widths. Our revolutionary solution implies the use of octagonal shaped cores to reach a 99 % filling factor, with a significant saving on materials, and a correspondent improvement of no load losses (core losses), due to the extra 4-6 % of increased material. This process patented (patent no. 102017000022419 [1]) under the name of TWINCORE exploits the optimized results from the unification of core cutting and stacking implemented by an inline slitting head, covering the entire production process with only 2 different sizes of mother rolls and using a single automated machine, thus avoiding intermediate storages and reducing lamination scrap. Finally, the article will explore the optimization of the windings, resulting in a complete optimisation of the transformer’s most crucial components

Prediction of no-load losses of stacked 3-phase, 3-limb transformer cores

The work presented in this thesis can be utilised by electrical steel manufacturers and transformer designers to design energy efficient transformer cores possessing lower life cycle costs, thereby increasing financial gains. A novel computer based algorithm to predict losses of 3-phase, 3-limb transformer cores built with high permeability grain oriented steel (HGO) and conventional grain oriented steel (CGO) is presented. The algorithm utilises parameters like transformer geometry, global flux distribution, localised loss data and material properties thus enhancing the accuracy of the predicted results which were 1% of the measured values. This algorithm has contributed to new knowledge in the no-load loss prediction approach. Six, geometrically identical, 350 kVA stacked five packet 3-phase, 3-limb transformer cores assembled with HGO, CGO and four mixed combinations of HGO and CGO laminations in multi step lap (MSL) joint configuration were tested for the global flux density distribution and no-load loss. The investigation results are novel and suggest that the bolt hole diameter (slot width) and lamination width ratio affects the packet to packet variation of . This is a new contribution to the flux distribution regime in transformer cores. The no-load loss experimental results are novel and suggest that the variation of no-load losses with CGO content in mixed cores was non-linear because of the packet to packet variation of . This is a new contribution of knowledge in the field of mixed core loss behaviour. Novel data sets of localised specific loss increase and localised relative permeability decrease around different sizes of holes and slots for HGO and CGO were processed from data obtained by two dimensional finite element (FE) analysis. The data sets are a new contribution in the field of predicting localised magnetic properties around holes and slots

Core losses in partial core transformers

The University of Canterbury High Voltage Laboratory frequently uses partial core resonant transformers to conduct high voltage testing within the New Zealand power industry. These transformers utilise a non-standard core design in which flux is not constrained around the entirety of its path. This results in characteristics which are beneficial for high voltage testing, but also have negative consequences. The most significant of these consequences is a noticeable increase in losses, resulting in higher primary currents and a reduction in resonant effects. Present models are unable to estimate this loss in any accurate sense, instead relying on the experience of designers. In order to better understand these losses, this thesis describes a study into the quantification of core losses within partial core transformers. Previous studies are reviewed relating to the design and modelling of partial core transformers, and learnings and criticisms of these studies are offered. Theories relating to magnetic material loss derivation are collected, these theories relate to the traditional components of hysteresis and eddy current loss, and also to the more contemporary theories regarding excess loss. A method of specification, design and construction for the cores of partial core transformers is developed. This method is used to create an inventory of partial core transformer cores, as well as providing numerical representation of the dimensions of these cores. Testing is completed and described alongside relevant theory in order to determine what modes of core loss are present within partial core transformers, and to what amount these separate modes contribute to core loss. From this work it is determined that hysteresis is the dominant contributor to core losses, with lesser amounts of eddy current loss contributions. Excess losses are determined to contribute no meaningful losses. Finally, an FEM model is developed taking into account the anisotropic and nonlinear nature of the core. This model is used to investigate flux distribution within the core, and this distribution is then combined with relevant theory to produce a model able to accurately estimate losses within the core. This model is shown to agree with the results of testing, provide a more accurate estimate than present models, and also to correctly determine where heating effects will occur within the core

Enhancement of Inductive Power Transfer Technology: Iron-based Nanocrystalline Ribbon Cores

Inductive power transfer (IPT) has been studied extensively during the last decades, particularly for electric vehicle chargers (EV). Inductive chargers offer several advantages over standard plug-in ones. First, they reduce user interaction increasing comfort and mitigating safety concerns. Furthermore, they allow for the automation of the charging process and the implementation of opportunity charging schemes. Thus, distributed charging points can be deployed in strategic locations — such as traffic lights, public and private parking places, etc.— and EVs can be charged more frequently. This reduces the depth of discharge of the battery and increases its lifespan. Furthermore, IPT systems with bidirectional power flow can facilitate the adoption of vehicle-to-grid schemes (V2G). IPT technology is reaching a mature state. Nevertheless, several aspects of the technology can still be improved. First, the state-of-the-art systems are sensitive to misalignments between the transmitter and receiver pads. Second, the complete standardization of the pad's design has not yet been achieved. Consequently, the interoperability of systems designed by different manufacturers is not yet guaranteed. Third, the detection of foreign objects between the pads is a problem that has not been completely solved. Last, the power density of the pads can still be improved. Pads are generally large and heavy which hinders the adoption of this technology. This dissertation addresses some of these problems in an attempt to enhance the state-of-the-art of IPT technology. The largest portion of this thesis is dedicated to the study of alternative core materials for IPT charging pads. In particular, nanocrystalline ribbon cores are considered a promising material. This material offers a higher saturation flux density, a higher permeability, superior thermal performance, and mechanical robustness compared to the standard MnZn ferrites commonly used in IPT systems. A feasibility analysis of this material was carried using intricate finite element models and experimental measurements. The analysis concluded that higher power densities can be effectively achieved with nanocrystalline ribbon cores. However, eddy-current losses on the outer/lateral faces of the cores were identified as problematic. This motivated a new design approach in which the unique properties of this material were considered during the design stage. Guidelines for the design of nanocrystalline ribbon cores were derived. These were applied to the design of a WPT3, 11 kW pad. These pads showed superior performance as compared to identical pads with ferrite cores. Pads with nanocrystalline cores were 2% more efficient and achieved an 11% higher coupling factor. Likewise, up to 25%, lower flux leakage was obtained. Moreover, their performance concerning temperature variation outperformed the one from ferrite cores both in heat dissipation and thermal stability. Finally, the pads were tested near magnetic saturation. Nanocrystalline cores were able to transfer more power before reaching this point. Thus, higher power densities were achieved with this material. Finally, methods for reducing the eddy-current losses in the system were tested. Ferrite shielding, in particular, was found to be an effective method to improve efficiency and homogenize the temperature distribution within the core. As a minor contribution, a control strategy that uses the dual-resonant frequency characteristic of LCCL-compensated pads is also presented. This strategy was validated experimentally, and it can be used to increase the power transfer capability of pads under misaligned conditions. Moreover, this strategy can ease the interoperability of IPT pads designed by different makers which have different ratings and dimensions