Delta Transformer Research Articles

PERFORMANCE STUDY OF UNBALANCED LOAD ON OPEN DELTA TRANSFORMERS

A transformer is a device that can transfer (transmit) and change electrical energy from one electrical circuit to another with the same frequency based on the principle of electromagnetic induction. The transformer that will be used in this research is a three-phase open delta connection transformer, which is connected to a delta connected load. If one of the three phase windings in the delta connection transformer is damaged, then the remaining two windings can be implemented or designed into three phase open delta connections, which can be used to distribute three phase electrical power to the load. The performance of the unbalanced load influence on the open delta transformer, when it is loaded with an unbalanced load that is not the same size on each phase, causes an increase in current on each phase, resulting in an increase in the input power absorbed by the unbalanced load resulting in power loss. larger (losses) with reduced efficiency. The aim of the research is to study the performance of unbalanced loads on open delta transformers and the research method is an experimental method in the laboratory, which includes testing on three-phase open delta transformers in unbalanced load conditions. The measurement results show that there are differences in performance (output results) in the influence of unbalanced loads between the average current and losses and the efficiency of the open delta transformer.

48-Pulse Voltage-Source Converter Based on Three-Level Neutral Point Clamp Converters for Solar Photovoltaic Plant

The demand for high-power converters for use in large-scale solar photovoltaic (PV) plants increases as the plant size continues to grow. The multipulse voltage-source converter (VSC) configurations are the viable option for high-power solar PV converter applications because they improve conversion efficiency due to low switching losses and allow direct integration with a medium-voltage (MV) grid. In this article, a 48-pulse VSC based on the fundamental frequency switching (FFS) three-level neutral point clamp (NPC) converter with a start–delta transformer configuration is used for large-scale solar PV plant application. It is also used as a PV-static synchronous compensator (STATCOM) to provide the required reactive power support to the grid to regulate the voltage. The solar PV plant configuration for a 100-MW capacity is modeled in MATLAB and implemented in the real-time OPAL-RT platform to verify its design and controls. The harmonics, static, and dynamic performances are demonstrated in detail.

Parallel Perturbed Gauss-Newton State Estimator Based on Fortescue Transformation for Unbalanced Power Systems

This letter extends the complex-variable perturbed Gauss-Newton method to estimate the state of unbalanced power systems by exploiting the Fortescue transformation. It proposes a novel and efficient graph-based way to deal with singularities due to zero-sequence network parts bounded with delta transformer windings and isolated from the ground. The estimator can handle both phasor and complex power measurements. Compared with the standard complex-variable unbalanced state estimator, it achieves better numerical stability and a speed-up of around three times using a sequential implementation and five times using parallel execution.

Power quality improvement by using multiple sources of PV and battery for DSTATCOM based on coordinated design

This paper presented the effect of using multiple sources of photovoltaic (PV) cells and battery on the input dc link channel of voltage source converter (VSC) for distribution STATCOM (DSTATCOM). The first high coordinated design is applied on the input of three-leg VSC for DSTATCOM to provide a continuous voltage over the time without delaying or interruption in the power through the control circuit and Dc to Dc circuit for boost of photovoltaic cell and buck-boost of battery. When there is a large of sun radiation, the generating power of PV is supplied to the three-leg VSC of DSTATCOM for power demand compensation and the surplus power is saved at the battery. In the condition of night or cloudy days the battery is discharged to maintain the sustainability of the VSC DSTATCOM. In addition, the design is used a Star / Delta transformer to isolate three-leg VSC for DSTATCOM to provide a circular path for zero sequence fundamental and then reducing harmonics the neutral current. The purpose of using DSTATCOM is to reduce the harmonics of current source, compensate the reactive currents and compensate the ground currents in the point of common coupled (PCC). The type of algorithm that used to coordinate the compensation process of DSTATCOM is a synchronous reference frame (SRF).

Analysis of a Shunt Wye–Delta Transformer for Multi-Generator Harmonic Elimination Under Non-Ideal Phase-Shift Conditions

A 12-pulse converter has been commonly used for a large-scale power generating system. The arrangement of a delta–delta (Δ–Δ) and a delta–wye (Δ–Y) phase-shift transformer pair in series with the voltage source eliminates undesirable harmonics from nonlinear loads. Recently, a novel front-end for a multi-generator power system was proposed, which utilizes a single Y–Δ transformer to shunt between the two 30° phase-shifted generator outputs and results in the comparable harmonic elimination performance to the conventional 12-pulse rectifier. The shunt-type Y–Δ transformer front-end achieves more than 75% transformer size reduction, making it extremely attractive to large-scale industrial and shipboard applications. However, the exact 30° phase shift between the two rotating generators can drift in a practical system, especially under dynamic conditions. The harmonic performance under the non-ideal 30° phase-shift condition can deteriorate with the Y–Δ shunt-type front-end. To understand the impact of non-ideal phase-shifted generator sources, this paper derives the mathematical models through the use of an equivalent circuit, a square-wave analysis, and the phasor representation to show the harmonic cancellation principle and verifies the results with the computer simulation.

VCO‐less PLL control‐based voltage‐source converter for power quality improvement in distributed generation system

This paper presents the voltage-controlled oscillator (VCO) less phase-locked loop (PLL)-based control of voltage source converter. It is used in the distributed power generation system for improved power quality. This control extracts the fundamental component from the sensed load current using three phases to alpha–beta transformation without using VCO, unlike synchronous reference frame–PLL, where fundamental component extraction needs two transformations with the use of VCO. Owing to the absence of VCO in the proposed method, the computational burden of trigonometric operations is very less that results in a faster dynamic response under variable conditions. This characteristic makes it suitable for the distributed power generation system, where fast changes occur frequently. In this study, wind-based distributed generation system has been taken for study, which comprises of self-excited induction generator feeding non-linear load with varying electrical conditions. Using the proposed control, the reactive power compensation, harmonics reduction and load balancing are carried out in the system. In addition to it, neutral current compensation is also accomplished with the help of star–delta transformer connected at the load end. The system performances are investigated under steady state as well as in transient state and results are found satisfactory.

Ground Fault Protection Using Open Break Delta Grounding Transformer in Ungrounded System

One of the most common and difficult problems to solve in distribution power systems is the location and elimination of the ground fault. For the study of an electrical distribution network in ungrounded system operating at 20 kV on the primary and 380 V on the secondary. The model uses smaller nominal voltages consisting of 380 V on the primary and the secondary. The Ground fault protection system scheme uses over voltage relays and open break delta transformers, whereas for fault location detection using voltage transformers in star star connections.The highest single line to ground fault value is used for consideration of ballast rating selection. The single line to lowest ground fault value is used for setting the threshold on the voltage relay (59N). Referring to the result of the calculation of the highest single phase to ground voltage at point 1 is 144∠1800 volts, and the lowest point at 4 is 132∠1800 volts. A 200 ohm ballast impedance with 150 watts of power capacity, and an overvoltage threshold setting of 120 volts with TDS of 40. One phase fault protection mechanism works well at each point of interference, and voltage transformers are protected from overheating and damage.

Urbanización y naturaleza en el delta

El presente artículo analiza en perspectiva histórica tres lapsos de la historia y transformación del delta del río Guayas, con el propósito de examinar las contradicciones e interdependencias entre su urbanismo y su contexto natural. El estudio se basa en la idea de que una lectura crítica de la transformación urbano-ecológica del territorio en perspectiva histórica, puede aportar un entendimiento de la ‘urbanización de la naturaleza’ al considerar no solo la ciudad sino otros sitios y ecologías vinculadas a ella, las luchas políticas que les dan forma, y el desarrollo desigual. El estudio trae a la discusión temas clave sobre el urbanismo de Guayaquil y su interacción con el complejo hidrográfico del río Guayas: la ecología de los asentamientos precolombinos, la interdependencia moderna entre la transformación urbana y las conquistas ecológicas en el territorio, y el efecto de la expansión neoliberal en producción de la naturaleza.

A New PV Converter for a High-Leg Delta Transformer Using Cooperative Control of Boost Converters and Inverters

This paper proposes a new high-efficiency photovoltaic (PV) converter for grid connection through a high-leg delta transformer. The converter is composed of a symmetrically connected boost converter and three half-bridge inverters. One of the three half-bridge inverters is connected to the boost converter, and the others are directly connected to the PV terminals. As a result, this circuit configuration enables to reduce the power losses in both boost converter and inverters. This paper also proposes a new cooperative control method between the symmetrically connected boost converter and inverter. The control method can reduce the average switching frequency to 75% of that in a conventional one, resulting in a great reduction in the switching power loss. Experimental results confirm that the proposed circuit configuration makes it possible to improve its European efficiency from 91.6% to 94.5%. Moreover, system performance is evaluated on the assumption of maximum power point tracking operation.

Educational approach to the wye–delta transformations using simple circuit analysis techniques

The wye-to-delta (Y–Δ) transformation is part of every circuit analysis course. In electric circuits textbooks, the transformation is found by comparing the two networks and making sure that the resistance between each pair of nodes in one network is the same as the resistance between the same pair of nodes in the other network. The two networks are compared as open-circuit networks. This creates confusion among students because usually the network is part of a larger closed-circuit network. In this paper, an alternative method is proposed. The new method starts from one configuration and finds the corresponding equivalent configuration by deriving currents and voltages, as part of a closed circuit. This method can be adopted in circuit analysis courses to help students develop a deeper understanding of this topic.

A 20-Pulse Asymmetric Multiphase Staggering Autoconfigured Transformer For Power Quality Improvement

This letter presents a 20-pulse multiphase staggering autoconfigured transformer (MSAT) for power quality improvement in medium and high power applications. The proposed autoconfigured transformer is a combination of delta and zig-zag transformers. Contrary to the prior art multipulse autoconnected transformers, magnetic rating of the proposed configuration is only 40% of the load rating in addition to improved power quality indices. Moreover, the creation of a neutral point ascribed to inbuilt zig-zag windings supplements as one of the remarkable advantages of the proposed MSAT. Therefore, with this suggested configuration, the performance of zig-zag transformer is accomplished within the autoconfigured transformer. A detailed comparison of the proposed MSAT configuration with that of other multipulse autoconnected transformers in terms of magnetic rating and power quality indices are presented. Further, the feasibility and operability of the proposed MSAT are verified and validated through experimental tests on the laboratory prototype. The test results so obtained complies with the IEEE-519 and IEC 61000-3-2 standards on power quality requirements.

A Systematic Method for Finding the Input Impedance of Two-Terminal Networks

ABSTRACTWhen a network is a simple ladder network, its input impedance can be obtained simply using series–parallel reduction techniques. If there are bridging elements, such as bridged-T network or Wheatstone bridge, the network cannot be solved just by these techniques. Then one has to take the help of star–delta transformation. A systematic method is given for obtaining the input impedance of any complicated network. We shall deal with resistive networks first, and then all-L and all-C networks. Finally, more complex RLC networks in jw-domain are covered.

A New PV Converter for Grid Connection Through a High‐Leg Delta Transformer Using Cooperative Control of Boost Converters and Inverters

SUMMARYThis paper proposes a new high‐efficiency photovoltaic (PV) converter for grid connection through a high‐leg delta transformer, which is composed of a symmetrically connected boost converter and three half‐bridge inverters. One of the three half‐bridge inverters is connected to the boost converter, and the others are directly connected to the PV terminals. This circuit configuration enables to reduce the power losses in both boost converter and inverter. This paper also proposes a new cooperative control method between the symmetrically connected boost converter and inverter. The control method can reduce the average switching frequency to 75% of that in a conventional one, resulting in a great reduction in switching power loss. Experimental results show that the proposed circuit improves its European efficiency from 91.6% to 94.5%.

Rapid evolution of water resources in the Senegal delta

In recent decades major water developments have led to an agricultural transformation of the Senegal delta both in Senegal and Mauritania. This otherwise, semi-arid region of the Sahel band now has an abundant supply of freshwater all year round mostly used for irrigation and urban water supply, including for the capital cities of the two countries. Archives from the Landsat satellites and in-situ hydrographs were used in this paper to retrace and analyse the hydrological changes that have taken place in the region since the middle of the 20th century. The satellite archives indicate that the area covered by irrigation increased by one order of magnitude from 73km2 in 1973 to ~770km2 in 2010. The observed hydrological changes are complex, multi-faceted and often of great magnitude. If the water cycle was representative of natural conditions in the early 1980s, it is now representative of a heavily modified system controlled and impacted by human activities. The first hydraulic infrastructure was installed in 1947 to enable the Lake of Guiers to become the main water supply for Dakar. Two large dams were built on the Senegal River in the mid-1980s that modified the hydrological regime of the river by 1) preventing seawater intrusion, 2) raising the stage of the river and of Lake of Guiers and 3) moderating floods. Another recent hydrological change in the delta was the opening of river mouth in 2003, which has led to a reduction of the average water level while increasing the semi-diurnal tidal wave between the river mouth and Diama. Each phase of these river regime changes and each step of the irrigation expansion are expressed in localised changes in the physical groundwater system. Increasingly, the retroaction from the shallow aquifer systems is observed as a rise of the saline water table. This poses a threat to the environmental and agricultural value of the region, and the salinization of the soils. Mitigating actions for this threat are currently being envisaged by the authorities.

昇圧チョッパと連系インバータの協調制御を用いた電灯動力共用結線用ソーラーパワーコンディショナ

This paper proposes a new high-efficiency PV converter for grid connection through a high-leg delta transformer. The converter is composed of a symmetrically-connected boost converter and three half-bridge inverters. One of the three half-bridge inverters is connected to the boost converter, and the others are directly connected to the PV terminals. As a result, this circuit configuration enables to reduce the power losses in both boost converter and inverters. This paper also proposes a new cooperative control method between the symmetrically-connected boost converter and inverter. The control method can reduce the average switching frequency to 75% of that in a conventional one, resulting in a great reduction in the switching power loss. Experimental results confirm that the proposed circuit configuration makes it possible to improve its European efficiency from 91.6% to 94.5%.

Convergence analysis of the summation of the factorially divergent Euler series by Padé approximants and the delta transformation

Sequence transformations are valuable numerical tools that have been used with considerable success for the acceleration of convergence and the summation of diverging series. However, our understanding of their theoretical properties is far from satisfactory. The Euler series E(z)∼∑n=0∞(−1)nn!zn is a very important model for the ubiquitous factorially divergent perturbation expansions in theoretical physics and for the divergent asymptotic expansions for special functions. In this article, we analyze the summation of the Euler series by Padé approximants and by the delta transformation, which is a powerful nonlinear Levin-type transformation that works very well in the case of strictly alternating convergent or divergent series. Our analysis is based on a very recent factorial series representation of the truncation error of the Euler series. We derive explicit expressions for the transformation errors of Padé approximants and of the delta transformation. A subsequent asymptotic analysis proves rigorously the convergence of both Padé and delta. Our asymptotic estimates clearly show the superiority of the delta transformation over Padé. This is in agreement with previous numerical results.

Extending the Hydraulic Paradigm: Reunification, State Consolidation, and Water Control in the Vietnamese Mekong Delta after 1975

I IntroductionSurrounded by the sea to the east and south, and topographically shaped by the interplay of mighty rivers, mountains, deltas, and coastal plains, water is omnipresent in Vietnam. From ancient times, the economic basis of Vietnam's civilization was grounded in intensive irrigated rice production, an activity that requires sophisticated knowledge, skills, and technology in water control. The Vietnamese people can look back at a long history and grand tradition of managing water flows. The origin and cradle of Vietnamese civilization is in the Red River basin where floods, typhoons, and droughts occur frequently and in disastrous magnitude. Ensuring survival in this harsh and unpredictable environment has always required collective efforts in developing flood protection infrastructure and managing irrigation. Unsurprisingly, hydraulic management emerged as important function of the royal state administration in pre-colonial Vietnam. Protecting the nation and people from natural disasters was politically critical, since peasant rebellions and social unrests often arose in the aftermath of famines brought on by severe flooding and droughts (Smith 2002, 77; Tessier 2010,264). Etymologically, the Vietnamese word th?y l?i,1) a term of Chinese origin and best understood as hydraulics in the sense of water control and the utilization of nature by human, comprises connotations of water management that traditionally derive from the above mentioned utilitarian and technical orientation of human-nature relation.Compared to the Red River Delta, where human settlement and hydraulic interventions into the deltaic landscape go back as far as the beginning of the Christian era2) (Tessier 2010, 264; Tuan Pham Anh and Shannon n.d., 2), the making of the modern Mekong Delta, Vietnam's largest river estuary located in the Southwest of the country, commenced far later, but has been similarly bound up in the idea of humans striving for dominion over the natural world. Structural interventions imposed on the deltaic ecology, and the resulting environmental change, have been among the major contributors to the profound transformation of the Mekong Delta in modern history. In essence, the Delta's history can be divided into two epochs characterized by divergent human-society relations: first, people's adaptation to the Delta's complex hydro-ecology; second, people's efforts to tame and control the Delta's natural forces with the use of rational science and modern technology. The latter feature has prevailed over the past 200 years, as comprehensively traced by Biggs (2010). Particularly in the past 30 years, the need for regulating water flows in the light of flooding, salinity, and droughts, has modified profoundly the Delta's physical shape. Hydraulic engineers and planners played a critical role in this socio-ecological transformation of the modern Delta, where water management nowadays, is performed at a large scale through a dense system of water control infrastructure consisting of dikes, embankments, sluices, and partly pumping stations (Evers and Benedikter 2009a). With reference to Wittfogel's (1957) concept oihydraulic society, the delta's march toward total hydro-management has transformed the delta society from a traditional river-water civilization,3) 4 which used to live in tune with nature, into a modern hydraulic society4) which strives to exert control over the natural environment in which it is embedded (Evers and Benedikter 2009b).Along the path to total hydro-management, various intersections of water control, politics, and nation building were at the heart of the Delta's modern transformation. Similar to Swyngedouw's (1999; 2007) portray of Spain's departure from feudalism to modernity, a process driven by technological progress in water control, the Mekong Delta's changing socio-nature and transformation into a predominately human-made landscape can best be understood as part of hydro-social modernization . …

Effect of nucleation undercooling on the kinetics and mechanism of the peritectic phase transition in steel

The mechanism and kinetics of the peritectic phase transition in steel were studied by using a concentric solidification technique in a high-temperature laser-scanning confocal microscope. Strong solute diffusion fields are established during solidification of the primary delta phase, which leads to suppression of nucleation of the austenite phase, and hence the extent to which a steel can be cooled to a temperature below the equilibrium peritectic temperature before the peritectic reaction will occur. The magnitude of these diffusion fields was also determined as a function of carbon content, alloying additions, cooling rate and the fraction of primary delta phase that solidified before the peritectic reaction occurred. Depending on the extent of undercooling required to nucleate the first austenite platelet on the liquid/delta-ferrite interface, three different modes of the solid-state peritectic transformation of delta to austenite have been observed: a diffusion-controlled phase transformation that occurred by the progression of a planar interface; a diffusion-controlled transformation with cellular/dendritic morphology; and a massive-type of transformation. Under certain circumstances, a changeover between these modes has also been observed. The underpinning thermodynamic considerations that lead to these different modes of transformation are discussed and a new explanation is provided for the occurrence of a massive transformation of delta-ferrite to austenite. The relevance to and implications of these new findings to the continuous casting of steel of near-peritectic steel composition are also discussed.

Harmonic and Unbalance Compensation Based on Direct Power Control for Electric Railway Systems

This paper presents a general filtering and unbalance compensation scheme for electric traction systems using a direct power control-based algorithm. For a balanced three-phase three-wire system, the proposed method is able to control the power flow exchange between the grid and the load so that the instantaneous complex power is maintained constant. As a consequence, any nonlinear unbalanced load is seen by the three-phase supply as a balanced linear load. The proposed filter is evaluated on power substations with open delta (V-V) and Scott transformer feeders, and for two-level and dual-converter in the power stage. The scheme has been simulated and experimentally validated. The results from experimental and simulation tests show the controller advantages and the applicability of the proposed method in railway systems.

Photovoltaic based distribution static compensator for power quality improvement

This paper deals with a model of photovoltaic (PV) array or battery operated DC/DC boost converter fed three-leg VSC (Voltage Source converter) with star delta transformer for power quality improvement. A synchronous reference frame theory is proposed for three-phase four-wire DSTATCOM (Distribution Static Compensator) which includes voltage source converter and a dc link capacitor. The proposed DSTATCOM provides reactive power compensation, source harmonic reduction and neutral current compensation at the point of common coupling (PCC). The PV array or battery operated boost converter is used to step up the voltage to match the DC link requirement of the three-leg VSC. The main advantage of this proposed approach is that, it will provide continuous compensation for the whole day. The star/delta transformer provides isolation to the VSC and path to the zero sequence fundamental as well as harmonics neutral current. To derive the reference current in order to generate the firing pulse to the VSC, the overall system is designed, developed and validated by using MATLAB–SIMULINK environment.