Showing papers on "Isolation transformer published in 2002"

A Power Electronic-Based Distribution Transformer

Abstract: The distribution transformer has been in use by utilities throughout the twentieth century. Until now, it has consisted of a configuration of iron or steel cores and copper/aluminum coils, with mineral oil serving as both coolant and dielectric medium. Inherent in this type of construction are regulation, significant weight, losses, environmental concerns, and power quality issues. A new kind of distribution transformer is proposed for the twenty-first century, one that can be made self-regulating, oil-free, and able to correct power quality problems. A power electronic transformer has been analyzed, simulated, prototyped, and tested. Results of this effort, as well as the novel features of this new type of transformer, are discussed herein.

An actively cooled high power, high frequency transformer with high insulation capability

Abstract: An actively cooled high power, high frequency transformer with high insulation capability for use in a high power multilevel converter is discussed. The transformer is designed for a power level of 350 kW and is realized with amorphous core material and coaxial windings. Special attention is paid to the insulation problem, since the dielectric losses and the influence of the voltage waveform with very steep edges have to be investigated more in detail to guarantee a long lifetime of the device.

Universal serial bus voltage transformer

Abstract: The present invention provides a universal serial bus (USB) voltage transformer, which comprises a main body, a transformer circuit unit, and several connectors. The transformer circuit unit is disposed in or at the inside of the main body. The connectors are electrically connected to the transformer circuit unit directly or via a connection cable. A USB voltage transformer having travel charging function is thus formed. The USB voltage transformer of the present invention can simultaneously charge several portable electronic devices like mobile phones, personal digital assistants, electronic translators, and small cameras.

Power Transformers: Principles and Applications

Abstract: Complete with equations, illustrations, and tables, this book covers the basic theory of electric power transformers, its application to transformer designs, and their application in utility and industrial power systems. The author presents the principles of the two-winding transformer and its connection to polyphase systems, the origins of transformer losses, autotransformers, and three-winding transformers and compares different types of transformer coil and coil construction. He describes the effects of short circuits on transformers, the design and maintenance of ancillary equipment, and preventative and predictive maintenance practices for extending transformer life.

Design issues of a core-less transformer for a contact-less application

Abstract: A set of rules for designing coreless transformers for contactless applications is presented in this paper. In contactless transference of energy, there is a relative big separation distance between the coils, so coupling is low. Several simulations have been performed with an FEA tool studying different technologies and winding strategies in order to quantify the improvements in coupling and resistance for different gaps. The analysis has been done for the transcutaneous transformer of a human-body implant, but the conclusions can be extended to any kind of coreless transformer for a contact-less application. The results are consistent with the measurements.

Driving circuit for piezoelectric transformer, cold-cathode tube light-emitting apparatus, liquid crystal panel and device with built-in liquid crystal panel

Abstract: A driving circuit for a piezoelectric transformer is provided, which ensures lighting of all the cold-cathode tubes connected to the piezoelectric transformer, and reduces the difference in brightness between the cathode tubes during steady lighting, thereby enhancing reliability and performance. A plurality of cold-cathode tubes connected to a secondary side of the piezoelectric transformer, and a cold-cathode tube output detector circuit connected in series to a plurality of cold-cathode tubes, for detecting an output state of the respective cold-cathode tubes are provided, and the driving of the piezoelectric transformer is controlled based on a detection signal from the cold-cathode tube output detector circuit. Because of this, the piezoelectric transformer performs the same operation as that with respect to one cold-cathode tube.

Passive network tap device

Abstract: A tap device comprises a network entry connection, a network exit connection, and a network interconnection path there between. A high impedance tap circuit is electrically connected to the network connection path, and comprises an isolation transformer and active buffer element. Advantageously, a power interruption to said tap circuit does not affect network communications.

Design of an electronic power transformer

Abstract: For the distribution of electrical energy in Germany, application-specific transformers with ratings of 110/20 kV, 110/10kV, 40 MVA, 50 Hz are typically in operation. Due to their weight, these transformers can only be transported with great expense (usually by rail). Therefore a considerable number of reserve transformers has to be held in stock in each distribution area, to guarantee power reliability to utility customers by quick replacement. To reduce assets, a universal, mobile and flexible (adjustable to different medium-voltage levels and truck movable) transformer reserve unit is desired by utility companies. The modular design of an electronic power transformer for this purpose is given in this paper. Based on power electronics, additional features like fast voltage regulation, reactive power compensation, ride-through capability etc. are described.

Overview of different alternatives for the contact-less transmission of energy

Abstract: When a physical connection cannot exist between the power source and the load, a transformer is usually used as a power link to transfer the energy. Primary and secondary windings of this transformer are usually separated a distance that is quite large compared to its own size. This means that coupling is low and leakage inductance is higher or comparable to the magnetising inductance. Therefore, voltage gain is low and a considerable part of the primary current will flow through the magnetising inductance and go back to the power source. An important effort has been done in the last years, proposing different topologies suitable for contact-less applications and suggesting design rules in order to improve coupling of the contact-less transformer. This paper presents an overview of many of the proposals, comparing the converters results in terms of efficiency, size, coupling of the transformer and control method.

Highly efficient contactless electrical energy transmission system

Abstract: This paper proposes a new concept for a contactless electrical energy transmission system for an automated guided vehicle The system has rechargeable batteries on the vehicle and electrical energy is supplied at a specific place When electric power is supplied to the vehicle, it runs automatically and approaches the battery charger Therefore, a comparatively large gap is needed between the primary transformer at the battery charger and the secondary transformer on the vehicle in order to prevent damage which would be caused by a collision In this case, a drop of the transformer coupling rate due to the large gap must be prevented In conventional contactless electrical energy transmission technology, since electric power is received by a pick-up coil from a power line, a large-sized transformer is required And when the distance over which the car runs is long, the copper loss of the line also increases The developed system adopts a high frequency inverter using a soft switching method to miniaturize the transformer The system has a coupling rate of 088 for a transformer gap length of 10 mm and can operate at 91% efficiency

A transformer connection for multipulse rectifier applications

Abstract: In this paper, a polygon-connected transformer for multipulse rectifier applications is proposed. By using the polygon form on the secondary windings, the windings can be designed to have the same voltage and impedance. The proposed transformer connection can also be extended to autotransformer connection if a galvanic isolation is not required. By using the proposed autotransformer, the required kVA rating can be much smaller compared to the rated load.. The design and analysis of the proposed transformer connection are detailed. Several experimental results are included to show the effectiveness of the proposed method.

Rise time reduction in high-voltage pulse transformers using auxiliary windings

Abstract: Today high-voltage pulses are reaching more fields of application. High-voltage pulse transformers are often used in association with high-voltage pulse generating circuits to further increase the pulse output voltage level. However, because of the transformer parasitic elements involved, the transformer is the critical device in shaping the rising characteristics of the output pulse. One of the techniques usually adopted to decrease the leakage inductance of the transformer adds two auxiliary windings to the transformer. If properly used, these auxiliary windings reduce the leakage flux and, therefore, the leakage inductance. As a result the pulse rise time is reduced. In this paper, a mathematical model is used to describe the observed behavior of a transformer operating with auxiliary windings, based on the theory of electromagnetic coupled circuits. The model is discussed regarding the experimental results obtained from a high-voltage test transformer associated with a high-voltage pulse generating circuit, and the simulation results obtained from the numerical evaluation of the developed differential equations implemented in Matlab/Simulink with the measured transformer parameters.

Three-phase-to-four-phase transformer for four-phase power-transmission systems

Abstract: In this paper, a new three-phase-to-four-phase transformer with four-phase four-leg structure is first proposed, its electromagnetism principle is analyzed, and the properties and features of the transformer are also discussed. This transformer may be applicable to either four-phase transmission systems or autotransformer (AT) traction power-supply systems in electric railways.

Pick-up transformer for ICPT applications

Abstract: A novel pick-up for inductively coupled power transfer systems allows the generation of controlled outputs at very high voltage or current using semiconductor switches with modest ratings, and no extra conversion stage. The concept is developed of a 'pick-up transformer' from a theoretical viewpoint and its performance is illustrated with a practical example.

Power line communications apparatus and method

Abstract: A power line communications apparatus and method for providing communications over power leads connecting two pieces of electrical equipment. One power lead is split into similarly sized first and second parallel conductors. The first and second conductors pass through a current transformer, the first conductor having a load current flow opposite the second conductor with respect to the current transformer. The transmitted communications signal is applied to the secondary of the current transformer and is induced on the primary of the transformer, namely a loop formed by the first and second conductors. A second current transformer serves as a receiving transducer and senses the communications signal on the first and second conductors.

PWM half-bridge converter with dual-equally adjustable control signal dead-time

Abstract: A method and system of controlling half-bridge DC—DC converters to achieve Zero Voltage Switching (ZVS) for at least one of the switches. The soft-switching half-bridge DC—DC converter system includes soft-switching for all switches by adding an additional branch with a switch and a diode across the primary side of an isolation transformer and by applying a Duty-Cycle Shifted PWM Control.

HVDC-transformers-a technical challenge

Abstract: Design and manufacturing of HVDC-transformers and smoothing reactors for high DC-voltages are still very special devices and the number of manufacturers is limited. The paper analyses the components of HVDC-transformers and reactors in more detail and shows the influence of DC-operating conditions. The core looks very similar to conventional AC-transformers since it has to fulfil the same physical tasks. The designer has to recognise additional features like DC-currents which can oversaturate the core and probably overheat it and change completely the noise level and noise spectrum. The windings of HVDC-transformers look also very similar to AC-transformers. Additional losses by current harmonics are not so special for transformer designers. A speciality are valve windings. Very high test-voltages in combination with low number of turns can be a challenge for the designer. The insulation structure between windings and to ground as well as valve side leads and bushings are different from AC-transformers. Field plots for AC-, DC- and polarity reversal describe the technical problem in more detail. The process of quality control with the elements of material selection and control, component specification and testing of components needs more attention. Especially the process of adjustment of design of valve leads and valve bushings under the influence of various stresses and on site conditions is discussed in detail. The testing of HVDC-transformers is based on standards and customer specifications. The manufacturing process of HVDC-transformers differs partly from conventional transformers. Some examples are described in the paper.

Power system for supplying stable power

Abstract: A distributed power system, wherein a backup boost transformer is connected between a PFC transformer and a FE DC transformer. The backup boost transformer is also parallel connected with a diode. The backup boost transformer only operates in the sustaining time, if the first DC voltage drops gradually, the backup boost transformer will increase this first DC voltage and stabilize it at a preset voltage of the FE DC transformer. Therefore, the capacity of the storage capacitor of the PFC transformer can be fully utilized to have a longer sustaining time and decrease the variation range of the second DC voltage so as to enhance the efficiency and power density thereof.

Electric power supply feeder and electric power supply feed system and method of support for electric power supply feed system

Abstract: PROBLEM TO BE SOLVED: To enhance energy efficiency and to minimize power cast, in an electric power supply feed system as a whole. SOLUTION: An electric power supply feeder 1 comprises an AC input circuit 2, DC input circuit 3, and a plurality of output circuits 4 of AC or DC. The input circuit 2a to which commercial power is supplied is connected to a change- over part 11 through a detection part 6 which detects a voltage and a phase. An AC-DC converter 7 converts the AC input circuit 2 to DC, a DC-DC converter 10 converts the DC input circuit 3 into DC and then outputs to the changeover part 11. A DC-AC inverter 8 converts the DC input circuit to AC and then outputs to the changeover part 11 through an isolation transformer 9. The change-over part 11 connects AC power supply or DC power supply obtained from the commercial power input 2a, the AC-DC converter 7, DC-AC inverter 8 or DC-DC converter 10 to the output circuits 4 in random fashion, according to the control of a control part 12.

In-service testing of current transformers

Abstract: A system and method for testing an on-line current transformer is provided. The current transformer includes a primary winding and a secondary winding. An operating current continues to flow through the primary winding during testing of the current transformer. A controllable load is applied to the current transformer secondary winding. The controllable load is varied over a range of load settings including a maximum current setting and a maximum voltage setting. At a plurality of load settings within the range of load settings, a current flowing through the current transformer secondary winding is measured. Also, a voltage across the current transformer secondary winding is measured. An actual excitation curve is generated from the measured currents and voltages corresponding to the plurality of load settings.

Device and method for testing a transformer

Abstract: Method for testing a measurement transformer in which a test signal with a smaller frequency than the nominal frequency of the transformer is applied to the transformer and used to measure a number of frequency independent parameters, especially Eddy current resistance and the transformer hysteresis curve. These are used to create a transformer simulation model that simulates transformer behavior at different frequencies. The behavior of the transformer secondary side is investigated using the model, in particular the behavior of terminal voltage and current. An Independent claim is made for a testing device for testing a transformer, with a testing signal source (2), a measurement arrangement (4) for measuring transformer parameters and an evaluation unit (5).

Medium voltage drives: are isolation transformers required?

Abstract: Traditionally isolation transformers are used on medium voltage motor drives. Although this provides a means for reducing harmonics, reducing voltage stress on motors, it increases the size, cost, complexity and losses of the drive system. With the implementation of alternative topologies and new pulse width modulation switching patterns, these goals can be achieved without the use of an isolation transformer. The paper presents the topology and the techniques that can be utilized and proposes an overall AC motor drive system without the need for the transformer. Experimental results on a 600 hp, 4160 V motor drive are also included.

Integration of power transformer monitoring and overload calculation into the power system control surface

Abstract: Failures of power transformers as most valuable transmission system resources can cause high financial damage Therefore on-site transformer monitoring was introduced in order to steadily analyze the operating conditions Additional online transmission of certain monitoring values to the power system control centre enables to continuously assess the transformers' internal thermal status and further the admissible overloading duration under given circumstances If the results are immediately being displayed within the used power system control surface, the operators are given useful support in decision making, especially in critical network situations

Development of a contactless power converter

Abstract: The contactless transformer is an important requirement for industrial applications. It eliminates the metal contact restriction for power conversion. The present research is concentrated on the large air-gapped transformer such that the power transfer is based on such arrangement. The leakage inductance and the leakage field is the challenge. A model of the transformer the experimental waveforms and analysis of a power converter based on the gapped-transformer are presented. The length of air-gapped has been increased to 1 cm and the performance is satisfactory. Design criteria and consideration is also presented and discussed. Two converter based on the contactless transformer were built and tested.

Resonant driving control for low power supplies with piezoelectric transformer

Abstract: A resonant driving scheme for low power supplies using a piezoelectric transformer is presented. The proposed method, by exploiting the resonance of an additional inductor with the piezoelectric device input capacitance, allows the piezoelectric transformer to be driven at high efficiency independently of the matching between the inductor value and transformer characteristics. At the same time, the solution also allows the output voltage to be regulated by means of a feedback which controls the input voltage frequency by varying the inductor charge time interval. To verify the proposed scheme experimental results are given.

Multiple-port gigabit ethernet distribution switch

Abstract: An apparatus is provided for deployment in an outdoor environment for managing and distributing Ethernet-type data communication signals. The apparatus includes electrical isolation elements for various electromagnetic effects and a high speed pulse reshaper and repeater. The isolation elements include low capacitance electric pulse suppression devices so that maximum signal distance can be achieved without loss of usable pulse shape and isolation transformers on differential signal pair that retain magnetization at elevated temperatures so that signals are not blocked. As a further feature, a management protocol is included whereby the type of signals can be autonomously distinguished, managed, secured and redirected, thus allowing the apparatus to be operated with compatible devices in a daisy-chained and start switch fabric.

An analysis of transformer excitation current under nonsinusoidal supply voltage

Abstract: In this paper, the effect of nonsinusoidal supply voltage on the core loss and the transformer excitation current is investigated. The time-domain waveform of the transformer excitation current is calculated for a worst-case harmonic composition of supply voltage.

Capacitive voltage transformer

Abstract: A capacitive voltage transformers for distribution of the power of 10kv high potential line, includes a insulating column with a high potential terminal, a ground terminal and capacitors C1 and C2 in series connection. The column is filled with oilless dry filler. The capacitors C1 and C2 formed by a plurality of separated metallized film capacitors respectively in series or in parallel connection. At the tapping point between the capacitors there is a leading-out terminal of the secondary voltage which is connected to an induction transformer L in parallel. The transformer includes a frame with “C” shaped iron cores and windings wound around the cores. One of the said windings is the primary impedance winding, and the other is the secondary winding of the transformer. There is an over-voltage protector P connected in parallel between the tapping point and ground. A capacitive voltage divider is integrally combined with the transformer to provide a small volume, low cost device with a savings in materials. A highly accurate highly stable highly energetic secondary electric power supply is provided at or under 220V from a 10kv line. The load is completely isolated from the high potential with the load characteristics being greatly improved

Piezoelectric transformer and strobe apparatus having the piezoelectric transformer

Abstract: A strobe apparatus has a discharge capacitor charged by a voltage generated in the output voltage when a piezoelectric transformer is driven in the first resonance mode, and a discharge tube is triggered by a voltage generated in the output electrode when the piezoelectric transformer is driven in the second resonance mode. The transformer has two types of output electrodes and on one surface in the longitudinal direction and two opposing surfaces in the lateral direction. It can be driven by properly switching first and second resonance modes different from each other.