No-load Voltages Research Articles

Real-time Dynamic Eccentricity Detection by Analyzing Harmonic Components of No-load Line-line Voltages in Multi-three-phase PMSMs

Real-time Dynamic Eccentricity Detection by Analyzing Harmonic Components of No-load Line-line Voltages in Multi-three-phase PMSMs

Development of an efficient voltage regulation mechanism for switched capacitor converter with exponential gain

The compact switched-capacitor converter with exponential gain and modular design has been adopted in this paper. Two approaches have been applied to improve the efficiency by providing multiple no-load voltages. The first modifies the switching strategy to bypass the gain of one or more stages. The second introduces modified design that provide additional no-load voltages through alternative current paths. The voltage regulation is implemented by two control loops: The outer loop is designed to produce the minimum feasible no-load voltage and the inner loop adjusts the duty ratio of the switching signals to regulate the voltage to meet the desired reference. Switched capacitor converters have been used as voltage multipliers with constant voltage gain. The efficiency of a switched capacitor converter depends on the ratio between regulated to unregulated output voltage. Therefore, output voltage adjustment of these converters causes a significant efficiency reduction. By providing multiple no-load voltages within the output voltage range the efficiency of the switched capacitor converter can be improved. The proposed design has been applied to a three-stage converter to provide six no-load voltages. Simulation results demonstrate that the average efficiency over the entire output voltage range is more than 90 % of its maximum efficiency of the unregulated switched capacitor converter which reflects the effectiveness of the proposed scheme. This paper offers an efficient method to regulate the voltage of a modular switched capacitor converter with exponential gain. The advantages of the proposed design are small number of added components, does not require additional sources and suitable for higher power range

Series Capacitive Compensation to Increase the Railway Traction Power Supply System Transmission Capacity

The article addresses the problem of improving the numerical analysis and operation of series capacitive compensation (SCC) units in the return wire of 25 kV power supply system traction substations to increase the railway capacity. Numerical analyses of the SCC impedance for two versions are considered: according to the condition of voltage equalization in the traction substations power supply arms and according to the condition of minimizing the negative sequence voltage. It is shown that the existing regulatory documents correctly place focus on the SCC impedances determined from the condition of ensuring equal power supply arm voltages. It is also shown that for numerical analyses of SCC impedance, the connection of the 110(220) kV power supply line impedances should be taken into account. To this end, it is proposed to connect, in the equivalent analysis circuit diagrams, two adjacent substations to the external power supply system through an equivalent delta of the impedances of 110(220) kV power lines. To effectively increase the voltage in the traction network while maintaining the minimum equalizing current values, it is advisable to connect the SCCs at both adjacent substations. In so doing, the no-load voltage values should be kept at the same level to reduce the equalizing current first component, which is determined by the difference of the transformers’ no-load voltages. It is shown that the connection of the SCC does not entail a growth in the equalizing current second component, which is determined by the difference of voltage losses at adjacent substations, including the voltages across the SCCs. If the SCC is connected at only one substation of the inter-substation zone, it is advisable to introduce automated control of the transformer OLTC at the substation without an SCC with a limited number of switching operations (up to 10 per day) with increased loads in the traction network.

Maximum resolution of switched capacitor converter: a graphical approach

The efficiency of a switched capacitor converter can be represented as the ratio of the output voltage to open-circuit voltage. Switched capacitor converters with adjustable gain are designed with multiple no-load voltages to obtain higher efficiency over the voltage control range. This paper aims to realize the maximum resolution of a switched capacitor converter. A graphical representation of the output voltages formation has been proposed. The voltage composition diagram reveals a switching pattern of the multiphase operation cycle that leads to the desired output voltage. The proposed method has been applied to determine all possible output voltage levels that lead to maximum resolution. A three-capacitor converter has been controlled with the proposed scheme. The simulation results show that the output voltage follows the reference voltage closely. The converter provides 60% more output voltage steps compared to the nearest comparable design in the literature.

Research on vibration characteristics and Multi-parameter state recognition of ± 500 kV converter transformer under fluctuating conditions

The vibration of the winding and the iron core is the main source of the vibration of the converter transformer tank, and the vibration measurement and characteristic analysis are the judgment basis for its condition monitoring and identification. Compared with AC transformers, the vibration mechanism and vibration characteristics of converter transformers under fluctuating operating conditions are imperfect. Aiming at the special tank structure and considering the fluctuation of operating conditions, this paper establishes a multi-channel vibration measurement system for online identification of the operating status of the converter transformer, and extracts the characteristics parameters of the vibration signal in the time domain, frequency domain, and energy, and analyzes the differential distribution characteristics of winding vibration under different load currents, iron core vibration under different no-load voltages, and combined vibration during online rated operation. Finally, a method for identifying the operating status of converter transformers based on multi-characteristic parameters is proposed. The research results show that the characteristic parameters such as tank vibration intensity, maximum vibration frequency, and frequency band energy fluctuate with the operating status of the converter transformer, and there are obvious changes. Vibration measurement and characteristics of multi-characteristic parameters can be used to provide a theoretical basis and solution ideas for the operation status identification and early fault detection of converter transformers.

Experimental study of vibration characteristics of 110 kV oil-immersed transformer

As the voltage level and capacity of power transformer continue to rise, this results in its increasingly prominent vibration and noise problems. In this article, we study the vibration characteristics of the 110-kV oil-immersed transformer by means of experiments. Under different no-load voltages and short-circuit currents, the vibration signals in different positions and directions of the transformer are monitored respectively, and the vibration laws are analyzed. First, the vibration law of transformers is closely related to the operating conditions of transformers, which directly affects the frequency components of transformer vibration and the amplitude corresponding to different frequencies; second, it is found that the vibration law of transformers facing different directions will change under different operating conditions; and third, it summarizes the vibration of transformers in different positions under different operating conditions. These results can not only be used as the experimental basis for the theoretical research on large-scale transformer noise but also provides experimental support for the research on vibration reduction and noise reduction methods of large-scale transformer in engineering.

Proteksi Katodik pada Elektrode Zn Metode Sacrificial Anode untuk Peningkatan Kinerja Sistem Akumulator Air Laut

Corrosion to the Zn electrode in the seawater accumulator system can be controlled by the cathodic protection of the sacrificial anode system. The mechanism is via anode sacrifice such as Al which has a negative potential connected to the Zn structure to provide extra electrons. The Zn electrode design is protected by an Al offering anode to form Cu-ZnAl electrode pairs arranged in series to form a seawater accumulator. Testing of electrodes with sacrificial anode system cathodic protection (Cu-ZnAl) compared to unprotected electrodes (Cu-Zn) for 48 hours showed no-load voltages of 10.19 V (Cu-Zn) and 12.89 V while the power generated was 48.36 mW and 49.37 mW. The average power after 3 watt LED loading was obtained 12.03 mW (day 1) and 12.56 mW (day 2) for the Cu-ZnAl electrode, while the Cu-Zn electrode obtained an average power of 6, 68 mW (day 1) and 10.09 mW (day 2). The corrosion rates after two days of using the Cu-Zn and Cu-ZnAl electrode pairs were obtained 0.008136 mm/year (Zn) and 0.0749626 mm/year (ZnAl).

A New Solution for Sea Wave Energy Harvesting, the Proposal of an Ironless Linear Generator

The paper investigates an innovative ironless linear generator, installable inside a wave energy converter, in order to produce electricity from sea waves. This energy source is considered strategic for the future, especially in small islands; however, this technology is still far from the commercial phase. Considering the wave energy potential of the Mediterranean Sea, a first prototype of the electrical linear generator was realized at the Department of Engineering of Palermo University. This machine can be run by a two-floating buoys system, able to produce a linear vertical motion. The main goal of this paper is the investigation of the advantages and the disadvantages of the utilization of steel materials to realize the stator of linear generators. Thus, starting from the prototype, the authors analyzed the effects produced by the replacement of steel in the stator with a non-magnetic material. For comparison, the authors evaluated the amplitude of no-load voltages, using a three-phase connection scheme, and the amplitude of the magnetic force produced by the interaction of magnets with the stator. Both aspects were evaluated through numerical simulations and mathematical models.

Testing and Commissioning of a 135 MW Pulsed Power Supply at the Wuhan National High Magnetic Field Center

At the Wuhan National High Magnetic Field Center, two 67.5-MW pulsed power supply units have been installed to energize long-pulse magnets. Each unit based on a 12-pulse converter consists of two 6.9 kV/1.2 kV (1.0 kV) cast coil transformers and two six-pulse rectifiers connected in series. The units are connected to a 100 MVA/185 MJ inertial energy storage motor-generator set and can operate independently as well as in parallel or in series. Each unit is designed to provide no-load voltages of 3.2 kV (2.7 kV) and full-load voltages of 2.7 kV (2.25 kV) at the rated current of 25 kA for a 3-s pulse once every half hour. After completion of various performance tests, the power supply commissioning started in October 2012. At present, the power supply has energized a long-pulse magnet more than 100 times to produce flat-top pulses at various field levels, including a 50-T field pulse with 100-ms flat-top duration. In this paper, the final design of the power supply components is described in detail. Testing and commissioning results of the power supply taken with a dummy load and a long-pulse magnet are also presented.

Design of a 135 MW Power Supply for a 50 T Pulsed Magnet

At the Wuhan National High Magnetic Field Center (WHMFC) a 50 T/100 ms flat-top long-pulse magnet consisting of two coaxially nested coils is designed. The power and energy to operate the magnet is provided by a 100 MVA/185 MJ inertial energy storage motor-generator set. To accommodate the needs of this and future magnets, two 67.5 MW power supply modules based on 12-pulse converters are designed to convert the ac-power produced by the generator into controlled dc-power. The modules can operate independently as well as in parallel or in series. Each module consists of a combined input disconnect/grounding switch, two rectifier transformers, two parallel-connected 6-pulse rectifiers, a crowbar circuit, and a reversing switch. Two different transformer tap settings allow the module to provide no-load voltages of 3.2 kV and 2.7 kV and full-load voltages of 2.7 kV and 2.25 kV at the rated current of 25 kA for a 2 second pulse once every half hour. All components of the power supply modules are now under construction, with complete delivery and installation expected in early 2012. The design of the power supply components is described in detail. Digital simulation results of the power supply driving the 50 T/100 ms magnet are presented.

Finite Element Analysis of a Novel Design of a Three Phase Transverse Flux Machine With an External Rotor

The permanent magnet excited transverse flux machine is well suited in particular for direct drive applications of electric road vehicles. The novel single-sided design with an external rotor consists of a three phase arrangement with a total number of 120 poles. The 3D finite element model with completely independent rotor and stator parts includes only two poles of the machine with appropriate repeating periodic boundary conditions for the unknown degrees of freedom of the 3D magnetic vector potential. Thus, the various angular rotor positions can be calculated by utilizing the sliding surface approach and a domain decomposition algorithm. The results presented herein are focussed on the most important design parameters such as electromagnetic torque, no-load voltages and short-circuit currents.

Saturation Effects on Unbalanced Magnetic Pull in a Hydroelectric Generator With an Eccentric Rotor

We report an investigation of saturation effects on the unbalanced magnetic pull in a hydroelectric generator with 20% static eccentricity. We determine the magnetic pull force by the finite-element method in parallel with a simple analytical model for various no-load voltages and loads. Saturation significantly affects the magnitude of the unbalanced magnetic pull for high voltages and large loads.

The Ways of Making the Power Transformer’s Transformation Coefficient More Precise

Presented the method of determination transformation coefficient of power transformer, when known distance between primary and secondary windings. Given dependency between magnetic fluxes and no-load voltages. Transformation coefficients are express as functions of magnetic fluxes (main and leakage) and no-load voltages. Formulas are received with estimation of magnetic leakage fluxes for calculation of the number turn windings of multi-wound transformer under given turn ratio with inaccuracy not exceeding ±0,5%. Presented physical model of multi-wound power transformer, which allow calculate a number of turns of secondary windings for defined transformation coefficient. The Results of the work can be used when designing power multi-wound transformer with specifically exact transformation coefficient. Ill. 2, bibl. 5 (in English; summaries in Lithuanian, English, Russian).

Instrument for Automatic Measurement of the Parameters of Solar Elements

An automated instrument for measurement of the parameters of solar elements based on an IBM personal computer, a digital potentiometer, and V7-21A digital voltmeters is described. The instrument produces a programmed specification of the load impedance of the solar elements in the range 0.002–800 Ω, measurement of short-circuit currents up to 4 A, no-load voltages and the dark and light voltage-current characteristics as well as a calculation of the basic parameters of the solar elements with display of the results on a monitor and printer. The error of the measurements and of the calculation of the parameters of the solar elements is at most 0.4%.

Large signal nonlinear model of anisotropic transformers for nonsinusoidal operation. II. Magnetizing and core-loss currents

For pt.I see ibid., vol.6, no.1, p.174 (1991). No-load currents and voltages of saturated single-phase transformers are computed based on given lambda -i and harmonic core-loss characteristics. A circuit analysis approach is used to satisfy the nonlinear equations involved in an iterative manner. The theoretical and experimental analyses confirm that for the calculation of the iron-core losses under nonsinusoidal operating conditions the principle of superposition cannot be applied: the iron-core losses are dependent not only on the amplitudes of the fundamental and the harmonics of the flux density, but also on the phase shifts of the harmonics with respect to the fundamental. For the computation of the ohmic losses at no-load the skin effects within the windings are taken into account. To confirm the validity of the computed results some of them are compared with measurements.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

プロジェクション溶接現象についての研究 ＩＩＩ 電源特性と適正入熱制御方式の関連性

Based on the previous work, the regions of welding conditions were roughly decided by the electrode force and the, weld current in the power sources of drooping characteristics with different no-load voltages such as 3.3V and 6.3V. The region of the suitable welding condition was estimated by taking account of the indentation and the tensile shear strength.The indentation was found to be seriously affected by the initial splash during collapse of projection in the case of using the power source with no-load voltage of 6.3V and by the splash in the latter half weld time after collapse of projection in the case of using the power source with that of 3.3V. Especially the expulsive initial splash was responsible for the deformation of nugget shape, unstablity of tensile shear strength with a large amount of scatter and unstable failure of welds in the tear or the shear fracture at the rate about 50%. The tensile shear strength tended toward saturation immediately after the occurrence of the splash in the latter half weld time.In order to suppress these splashes and overcome these faults of the weld, the up slope electrode force was adaptively introduced in the power source with no-load voltage of 3.3V and the up slope control in the weld current at the initial weld time was remarkably adaptable in the power source with no-load voltage of 6.3V.

The Effects of Slotting on the Flux Distribution in Saturated High-Speed Homopolar Inductor Alternators

The effect of slotting not considered in previous papers, is analyzed by taking into account the actual slots of the stator. The equations and methods of Ref.l and 2 are used with some modifications. The boundary conditions at no-load on the lines of symmetry have been replaced by the value of the potentials and thus, improved convergence has been achieved. The flow chart of the main program for an IBM 7090 and the flow chart of an IBM 1620 program for calculating the potentials on the lines of symmetry are given. In a simplified solution, the actual slotted region is replaced by a smooth airgap and an equivalent " synthetic" region of homogeneous iron. The methods are used to calculate the no-load flux distribution and no-load voltage of a 95 KVA, three-phase 115/200 v, 3,400 cps., high-speed inductor alternator. The fundamentals and higher harmonics of the different solutions are compared. Calculated no-load voltages compare with test results very closely.