The Two-Stage Current Transformer
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This paper presents a brief discussion of the current transformer as used with measuring and controlling apparatus with special reference to the degree of accuracy which can be attained in the ratio and phase angle. A new type of current transformer is then described, in which it is possible to secure much higher accuracy with a given amount of iron and copper in the transformer. In this new device the transformation is effected in stages, the first yielding in the usual way a secondary current which is approximately correct in magnitude and phase, and the second yielding an auxiliary corrective current which, when combined with the first secondary current, gives a resultant current which very closely approximates to the secondary current which would be furnished by an ideal current transformer having no errors. The two currents may easily be combined by having two like windings in the devices operated, one for the main and one for the auxiliary secondary current. The mathematical theory of the two-stage current transformer is developed and applied. Experimental curves are given to compare the performance of the new transformer with that of an ordinary simple current transformer of good average performance. The effect of mutual inductance between the external secondary circuits is discussed, and some of the special advantages of the new transformer are given.Keywords:
Delta-wye transformer
Energy efficient transformer
Autotransformer
Leakage inductance
Transformer effect
Transformer types
This paper presents a new signal-phase electromagnetic transformer with an adjustable output voltage. The transformer uses a magnetic flux valve (MFV) to control the magnetic flux through the secondary winding. In this way, the amplitude of the output voltage induced across the secondary winding of the transformer can be adjusted continuously and quickly when the turn ratio and input voltage amplitude of the transformer are fixed. The configuration and working principle of the transformer are presented. A prototype of the proposed transformer was designed and constructed. Experimental results on the prototype were provided to validate the proposed transformer concept.
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This paper deals with the measurement, modelling and simulation of very fast transient overvoltages in layer-type distribution transformer windings. Measurements were performed by applying a step impulse with 50 ns rise time on a single-phase test transformer equipped with measuring points along the winding. Voltages along the transformer windings were computed by applying multi-conductor transmission line theory for transformer layers. The secondary voltage of the transformer was simulated with another model implemented in ATP-EMTP which takes into account the surge capacitance between the primary and secondary transformer winding. It was found that, when an impulse with a short rise time is applied, internal resonance occurs, which results in a very high secondary voltage. The computations were verified by measurements.
Autotransformer
Delta-wye transformer
Transformer effect
Leakage inductance
Energy efficient transformer
Emtp
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We previously proposed a Magnetic-Flux-Control transformer (MFC transformer). The MFC transformer has simple construction and high reliability because it consists of only a core and its windings. The MFC transformer can control output voltage and net inductance easily and continuously.For wide application and practical use, it is necessary to establish a design method for the MFC transformer. In this paper, we present an analytical method for the MFC transformer using Reluctance Network Analysis (RNA) and examine the characteristics of an MFC transformer.
Delta-wye transformer
Transformer types
Energy efficient transformer
Leakage inductance
Transformer effect
Magnetic reluctance
Autotransformer
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This paper presents a brief discussion of the current transformer as used with measuring and controlling apparatus with special reference to the degree of accuracy which can be attained in the ratio and phase angle. A new type of current transformer is then described, in which it is possible to secure much higher accuracy with a given amount of iron and copper in the transformer. In this new device the transformation is effected in stages, the first yielding in the usual way a secondary current which is approximately correct in magnitude and phase, and the second yielding an auxiliary corrective current which, when combined with the first secondary current, gives a resultant current which very closely approximates to the secondary current which would be furnished by an ideal current transformer having no errors. The two currents may easily be combined by having two like windings in the devices operated, one for the main and one for the auxiliary secondary current. The mathematical theory of the two-stage current transformer is developed and applied. Experimental curves are given to compare the performance of the new transformer with that of an ordinary simple current transformer of good average performance. The effect of mutual inductance between the external secondary circuits is discussed, and some of the special advantages of the new transformer are given.
Delta-wye transformer
Energy efficient transformer
Autotransformer
Leakage inductance
Transformer effect
Transformer types
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The transformer is one of the main components in the power network and transformer windings are one of the most expensive elements in the power transformer. Optimisation of winding distances is one of the most important parameters during the manufacturing of transformer. The distance between the windings in the two winding transformers is well known to transformer designers and manufacturers. However, insulation of the high voltage transformer with additional winding and tap winding is still a major problem for transformer designers. In this study, the additional winding to tap winding distance optimisation is made for a high voltage power transformer. Optimisation of the transformer's windings just not minimises the cost of the transformer but also increases the lifetime of the transformer. With additional winding and tap winding in high-voltage transformers, insulation distance is a major concern for minimising the cost and size of the high voltage transformer. In this study, an approach is made to balance the cost, size, and safety of high voltage transformers. The optimised distance and position between tap winding and additional winding are determined by using the finite element analysis. The finite element method results were also verified by making a prototype transformer.
Delta-wye transformer
Energy efficient transformer
Autotransformer
Transformer effect
Tap changer
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High-frequency transformer is the key component of the flyback converter,and its efficiency is directly related to the converter.In order to improve the inverter's efficiency,the optimum design of high-frequency transformer becomes very important.A 2D finite element model of the winding structure is built up to calculate the eddy current losses and leakage inductance caused by the different structure of flyback transformer winding.The laboratory prototype of the high frequency transformer has been designed,and the experimental results show that the transformer winding structure is reasonable,low leakage inductance,high efficiency and perfect output voltage waveform.
Leakage inductance
Delta-wye transformer
Energy efficient transformer
Transformer types
Transformer effect
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This article presents a new electromagnetic transformer with a continuously and quickly adjustable voltage ratio between the output and input. The transformer uses a voltage-controlled magnetic device called magnetic flux valve to control the magnetic flux through the secondary winding. In this way, the amplitude of the output voltage induced across the secondary winding of the transformer can be regulated continuously and fast when the turn ratio and input voltage amplitude of the transformer are fixed. The configuration and working principle of the proposed transformer are elaborated. A prototype of the proposed transformer was designed and constructed. The experimental tests are performed on the prototype to validate the proposed transformer concept and demonstrate its superior performance, including continuous and nearly instantaneous output voltage regulation capability, wide output voltage variation range, and high efficiency.
Delta-wye transformer
Energy efficient transformer
Autotransformer
Transformer effect
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To improve the power density of three-port high-frequency resonant converter using wide bandgap devices, a three-winding planar transformer is proposed. By analysing the topology and working conditions of the converter, the design requirements for the three-winding transformer are clarified. Based on the equivalent circuit of the three-winding transformer, the magnetizing inductance of transformer is directly and accurately controlled by the air gap of the core. The factors affecting the accuracy of air gap reluctance and transformer loss are analysed and some improved schemes are proposed. According to the optimized design process of the transformer, the method of selecting the optimal core size is given.
Leakage inductance
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Delta-wye transformer
Energy efficient transformer
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Air gap (plumbing)
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This paper studies the high-frequency high-efficiency transformer design. Several novel concepts are proposed to reveal the essence of the transformer design. In order to minimize the winding loss, several winding structure are proposed and compared. The planar transformer winding with PCB or spiral windings are discussed. The key factors to achieve the low winding losses are presented. The transformer design of the LLC resonant converter is investigated. The impacts on integration of magnetizing inductance and leakage inductance are studied.
Leakage inductance
Delta-wye transformer
Energy efficient transformer
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Autotransformer
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Sabatoga Springs, N. Y., June 25, 1925 J. F. Peters: In Mr. Dahl's paper, as far as I can see, the assumption is made that the triple-frequency component of magnetizing current follows Ohms' law, that is, there is inherently in the transformer a triple-frequency voltage and the triple-frequency component of current that will flow is that voltage divided by a triple-frequency impedance. If this is the ease, then by decreasing the triple-frequency impedance to a small value, the corresponding current could be made quite large. Obviously this cannot be the case because when the triple-frequency current reaches a certain value, which is approximately 40 to 45 per cent of the fundamental-frequency current, the voltage wave takes on a true sine shape in which case the triple-frequency voltage disappears. It may not be possible to decrease this impedance to a very small value within the transformer, but if it is a true impedance, it can be counteracted to any desired degree externally. Also, if no triple-frequency current is permitted to flow, there will be a large triple-frequency voltage appear across each of the phases. In a transformer of commercial proportions and flux density, this voltage would amount to approximately 75 per cent of the fundamental-frequency voltage, which, in the transformer analyzed by Dahl, would amount to 100 volts triple-frequency. Then the triple-frequency current that should flow in any winding-should be that voltage divided by this triple frequency impedance. He finds in winding one a triple-frequency impedance of approximately one-half ohm. This should give a triple-frequency current in the order of 200 amperes. Actual measurements show approximately two amperes.
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