Power Distribution Transformers Research Articles

Losses in Power Distribution Transformers

The paper presents the estimation of power losses in distribution transformer of Provincial Electricity Authority (PEA) distribution system at Muang district of Suphanburi province in Thailand. Data of 416 power distribution transformers composed of transformer (kVA), load current, no load loss and full load loss which were used for calculating energy losses. It was found that the total energy loss of all transformers is approximately 1,756,380 kWh/year.

Coordinated voltage control of a decoupled three-phase on-load tap changer transformer and photovoltaic inverters for managing unbalanced networks

The increasing penetration of fluctuating photovoltaic (PV) generation brings operational challenges for distribution system operators, such as introducing the voltage rise problem. The situation is made worse in the presence of single-phase generation being unevenly connected to the different phases. To address this problem, distribution transformers with single-phase tapping capability, together with reactive power provision of PV systems, are under investigation. This paper presents modeling and analysis of the benefits of coordinated voltage control of a decoupled three-phase on-load tap changer (OLTC) and photovoltaic inverters in a distribution system, for accommodating a greater number of photovoltaic generators in the grid. A 24h root-mean-square simulation study is performed in the DigSilent PowerFactory with a 1s time step using 10min resolution consumption and production profiles on a real Danish distribution grid, as well as the developed dynamic photovoltaic generation and load models. The simulations show that the joint action of the power distribution transformer with OLTC control on each phase, and the reactive power provision of photovoltaic inverters, significantly improves the PV hosting capacity in the analyzed unbalanced scenarios without side effects, such as additional power losses, or significant neutral voltage rises.

Formation and Effect of Moisture Contents to Kraft Paper’s Life of In-Service Power Distribution Transformer

Examples of solid and liquid electrical insulations for power transformer are mineral oil and cellulose based paper. As transformers performed their function to step-up or step-down voltage level, its’ insulations will be degraded. Paper insulation is considered the most critical component in a transformer insulation system because it is not easily replaced if compared to oil where it is easily reconditioned in-order to remove water and contaminants. Studies show that temperature, moisture contents and oxygen contributed to paper insulation degradation. Moisture and furanic compound were produced from these deterioration processes. This paper is focused on the formation and effect of moisture to Kraft paper’s life. Levels of moisture contents were obtained from in-service power distribution transformers. These data then is used to assess the Kraft paper’s life by means of Weibull plot. This study shows that level of moisture contents can be used to assess the life of Kraft paper insulation.

Smart Charging: System Design and Implementation for Interaction Between Plug-in Electric Vehicles and the Power Grid

Recent years have witnessed steady sales increase of electric and plug-in electric vehicles (PEVs). Stringent government regulations alongside persistent pressure from environmental groups will further increase the demand and sales of such vehicles. This trend might put pressure on the grid and local power distribution circuits and transformers. A sudden increase in power consumption, mainly caused by people charging their vehicles at the same time, and during the already peak load on the utility, may cause problems. These problems are mainly caused by the heavy demand on the local voltage transformers and the power sources. Power generation and distribution utilities may need to incur significant cost increases if this problem is not handled appropriately. In this paper, we present a novel design and implementation logic for a smart grid system that allows for dynamic interaction between electric/PEVs and the power grid. This smart and dynamic interaction will allow for safe and semi-stable load on the grid and thus minimizing the cost and preventing damage caused by the excessive loads. The complete system design is presented in this paper with emphasis on the developed algorithms. It has been implemented and tested on the Chrysler’s PEV RAM 1500 U.S. Department of Energy pickup trucks.

Simplified measurement-based black-box modeling of distribution transformers using transfer functions

Modeling of power distribution transformers in the high-frequency range is of crucial importance in cases such as using power-line communication technology or investigating transient overvoltages at the transformer low-voltage side. This paper presents a simple black-box modeling methodology for distribution transformers using transfer functions defined by the recorded voltage ratios at the transformer terminals. The model parameters are estimated using an optimization method that minimizes the error between the measured and the calculated data. A significant advantage of the proposed methodology is the use of conventional instruments in conducting the measurements rather than high-precision and expensive equipment. The accuracy of the developed model is verified by its implementation in both frequency- and time-domain simulations.

Impacts of high penetration level of fully electric vehicles charging loads on the thermal ageing of power transformers

Abstract This paper develops a methodology to determine the impacts of high penetration level of fully electric vehicles (FEVs) charging loads on the thermal ageing of power distribution transformers. The method proposed in this paper is stochastically formulated by modelling the transformer life consumption due to FEVs charging loads as a function of ambient temperature, start time of FEVs charging, initial state-of-charge and charging modes. FEVs loads are modelled using the results from an analytical solution that predicts a cluster of FEVs chargers. A UK generic LV distribution network model and real load demand data are used to simulate FEVs’ impacts on the thermal ageing of LV power distribution transformers. Results show that the ambient temperature, FEVs penetration level, and start time of charging are the main factors that affect the transformer life expectancy. It was concluded that the smart charging scenario generally shows the best outcome from the loss of life reduction perspective. Meanwhile, public charging which shifts a large percentage of charging load to commercial and industrial areas can significantly alleviate the residential transformer loading thus has little impact on the loss of life of transformers. The proposed method in this paper can be easily applied to the determination of the optimum charging time as a function of existing loads, and ambient temperature.

Continuous Wavelet and Hilbert-Huang Transforms Applied for Analysis of Active and Reactive Power Consumption

Abstract Analysis of power consumption presents a very important issue for power distribution system operators. Some power system processes such as planning, demand forecasting, development, etc.., require a complete understanding of behaviour of power consumption for observed area, which requires appropriate techniques for analysis of available data. In this paper, two different time-frequency techniques are applied for analysis of hourly values of active and reactive power consumption from one real power distribution transformer substation in urban part of Sarajevo city. Using the continuous wavelet transform (CWT) with wavelet power spectrum and global wavelet spectrum some properties of analysed time series are determined. Then, empirical mode decomposition (EMD) and Hilbert-Huang Transform (HHT) are applied for the analyses of the same time series and the results showed that both applied approaches can provide very useful information about the behaviour of power consumption for observed time interval and different period (frequency) bands. Also it can be noticed that the results obtained by global wavelet spectrum and marginal Hilbert spectrum are very similar, thus confirming that both approaches could be used for identification of main properties of active and reactive power consumption time series.

The Research and Application of Standard Modular all Insulation Transformer Station

In the power distribution network , transformer station is the most common device, which is related with the power supply security , the landscaping , and has the most maintenance .It is also a large number device that realize standardized equipment very difficult . According to the original power distribution transformer station which has poor ability to withstand the natural disasters, unreliable operation, the low intelligent level, non-insulation, easy to rust, backward technology, environment is not harmonious and other problems, adopt the industrial design concept and method, developing standard modular all insulation transformer station. New type transformer station materials are advanced and reliable, complete all insulation,free-maintenance,have effect for security, anti-corrosion, environmental protection, beautiful, portable, simple.Further ensure personnel and equipment security, convenient operation and management.This article respectively introduces from the new type transformer station research contents, technical route, play the role, application effect and so on.

Study on Risk Identification and Prevention of Power Transformer Based on Sampling Inspection Theory

Power transformer is one of the key equipment for power grid, and its quality has important effects to the security, stability and economic operation of the power grid. The government sampling inspection pass rate of 10kV power transformer is less than 80% in China, which causes serious impact to the product quality and brings serious security risks. It has great significance to study on the risk identification and prevention method. In this paper, the sampling inspection theoretical analysis of power transformer is carried out with the mathematical statistics and probability theory. Its application in the quality risk identification is studied on. The risk prevention effect of the sampling inspection is studied based on game theory. It is used both on the large scale power transformer and distribution transformer. The sampling inspection has the characteristics such as flexibility, randomness, science, and economics. It can be used in large range with flexible way, especially for the difficult test items. Random is the foundation for the scientific sampling inspection. The approach determines that it can reflect the population quality level with small cost, which has obvious economic benefits. In practice, sampling inspection should focus on the key aspects, including the design of sampling inspection plan, the selection of the sampling mode, the cost and the corresponding punishment.

Feature Analysis of Numerical Calculated Data from Sweep Frequency Analysis (SFRA) Traces Using Self Organizing Maps

This paper presents a comprehensive investigation of the Self Organizing Map (SOM) classification process of good and defective power distribution transformers. Three main features were extracted from the numerical calculation method of the Sweep Frequency Response Analysis (SFRA) signals acquired from the transformers. These features are the input vectors for the SOM classification. Analysis of the results has shown the capability of the features and the SOM classification method to differentiate between good and defective transformers.

Agent-based simulations of the influence of social policy and neighboring communication on the adoption of grid-connected photovoltaics

Agent-based simulations coupled with an analysis of the flow of electric power are carried out to examine the influence of the social policy of the government and the neighboring communication between customers on the adoption of distributed rooftop photovoltaic electrical power generators (PVs). How the relationships between the social policy and the possibility of a reverse current restriction give rise to the collective behavior of autonomous individuals, and how the end customers interact and form relationships with its environment are described. Strong intervention by the government in the areas near a main high-voltage power distribution transformer, where the possibility of a reverse current restriction is relatively low, drives the greatest adoption of the PV system. The near areas are primarily occupied by customers with only a PV to improve the diffusion rate of PVs via the self-organization by the communication between customers. It also lead in a decrease in the need for compensation devices, which in turn minimizes the social cost. Growth in the number of PVs in areas far from the transformer is assisted by the installation of batteries as compensation for the lost opportunity due to restrictions in those areas on reverse power currents. Therefore, excessive intervention by the government in the far areas results in an increase in the social cost of managing reverse currents.

Closed-Loop Control of DC–DC Dual-Active-Bridge Converters Driving Single-Phase Inverters

A solid-state transformer (SST) is a high-frequency power electronic converter that is used as a distribution power transformer. A common three-stage configuration of an SST consists of ac-dc rectifier, isolated dc-dc dual-active-bridge (DAB) converter, and dc-ac inverter. This study addresses the controller design issue for a dc-dc DAB converter when driving a regulated single-phase dc-ac inverter. Since the switching frequency of the inverter stage is much higher than that of the DAB stage, the single-phase inverter is modeled as a double-line-frequency (e.g., 120 Hz) current sink. The effect of 120-Hz current by the single-phase inverter is studied. The limitation of a PI-controller, low gain at 120 Hz, is investigated. Two methods are proposed to improve the regulation of the output voltage of DAB converters. The first one uses a bandstop filter and feedforward, while the second method uses an additional proportional-resonant controller in the feedback loop. Theoretical analysis, simulation, and experiment results are provided.

Метод частичных разрядов в диагностике силовых трансформаторов распределительных сетей нефтепромыслов

Метод частичных разрядов в диагностике силовых трансформаторов распределительных сетей нефтепромыслов

Active Filter for the Removal of the DC Current Component for Single-Phase Power Lines

Nonlinear loads and grid-connected converters can cause, in addition to the generation of several current harmonics in the grid current, a dc current component injection. A dc current component can cause the magnetic core saturation of distribution power transformers. Transformers operating under saturation conditions present increased power losses, overheating, and distorted current waveforms. Since a dc current component causes a small dc voltage component drop across the parasitic resistance of the distribution grid conductors, canceling the dc voltage component at the point of common coupling (PCC) implies the compensation of the dc current component injected/absorbed by electric loads or grid-connected converters connected at the same PCC. This paper proposes a low-cost nonlinear sensor for an accurate detection, free from offset problems, of the dc voltage component present in the grid voltage. The detection of the dc voltage component was used to realize an active filter of the dc current component. The proposed solution is outlined, and then the stability issue is addressed by means of a simplified model. Experimental results confirmed that the simplified model closely approximates the real system.

Detection Method of the DC Bias in Distribution Power Transformers

Nonlinear loads such as ac drives, switch-mode power supplies and grid-connected converters can cause, in addition to the generation of unwanted current harmonics, a dc current component injection into the grid. This dc current component can lead to magnetic saturation of the distribution power transformers, leading to higher current distortion and overheating. This paper presents a method to detect the dc current component flowing into the distribution power transformer with a precise measurement of the dc voltage component at the transformer winding. A magnetic sensor has been developed and implemented in a closed-loop control system to achieve a high sensitivity and guarantees a good linearity with a high rejection ratio to grid voltage variations. Simulation and experimental results confirm the effectiveness of the proposed approach.

A perspective on online partial discharge monitoring for assessment of the condition of rotating machine stator winding insulation

Partial discharges (PD) are small electrical sparks that can occur in liquid or solid insulation systems in high-voltage equipment, and can eventually cause failure of the equipment [1]–[3]. Partial discharge testing has been used for more than 80 years as a factory quality control tool to find manufacturing defects that could eventually lead to equipment failure. We believe that Johnson was the first to measure PD on operating high-voltage equipment, in the 1940s [4]. His aim was to find an online method to determine whether stator winding coils or bars were vibrating excessively in the stator magnetic core. These vibrating coils lead to abrasion of the high-voltage electrical insulation and to eventual failure. A symptom of the insulation abrasion process was that PD (or what he referred to as slot discharge) occurred between the surface of the coil and the stator core. By measuring the PD online, he could indirectly detect the movement of coils, which indicated that failure was likely. The measurement had to be made online because, if the generator were not operating, no magnetic forces would be acting on the coils; thus, the air gaps that are a necessary precursor of PD would not be as large. Johnson was successful in identifying those generators that were suffering the most from this problem, which was caused by the introduction of the first thermoset insulation systems and by workmanship variations that were magnified by an inadequate method of securing the coils in the stator slots for the novel insulation system. The success of the Johnson online PD measuring system inspired other machine manufacturers and even a few utilities to develop their own methods [5], [6]. The main reason Johnson needed online PD measurement was that loose windings do not produce as much PD when the motor or generator is not operating. Thus one of the important reasons for performing online PD tests is to monitor the condition of the equipment under normal operating electrical, thermal, and mechanical stresses. However, with the current emphasis on extending times between maintenance outages, and the push to reduce testing costs in general, the main reason now given for online PD measurement is to avoid shutdown of the equipment, which would be necessary for an off-line PD test or other diagnostic test. Although we believe online PD monitoring was first applied to rotating machines, the same reasons are valid for other electrical equipment, such as oil paper cable joints or terminations, distribution class switchgear, gas-insulated switchgear, and power transformers [2], [3].

Stray Losses Study for a Power Transformer Based on 3D FEM

Base on three dimension (3D) finite element method (FEM), a electromagnetic model for a power distribution transformer is established. The core loss, stray losses in structural components are simulated, the effects of magnetic shunts on tank losses are studied, then compared with experiments. The core loss, the decrease of stray losses when using magnetic shunts are in accordance with experiments. Studies indicate that tank loss is the most impartment part of stray losses in this model, magnetic shunts are effective in reducing stray losses.

A nonlinear Reactor for DC Current Compensation in Single Phase Power Lines

AbstractNon-linear loads and grid connected converters, whose utilization is constantly growing, have been causing problems regarding the power quality. These problems comprehend the generation of harmonics in the current provided by the power distributor. Among different kinds of deterioration, there is the issue of the DC current component. As a matter of fact, a DC current is detrimental for the distribution power transformer, as it leads to saturation the magnetic core. The saturation of the power transformer increases the VAR absorption, leading to possible damage the magnetic component due to overheating. This paper proposes a compensator system based on a non linear sensor that acts as an active filter for the DC current component flowing in the power lines. The paper is organized as follows: the first part outlines the strategy, then the stability issue is addressed by means of a simplified model. A simulation verification showed that the simplified model closely approximates the real system.

배전계통에서 전력용 변압기의 접지저항 영향에 관한 연구

A safe grounding design is used for providing means to carry electric currents into the earth under fault conditions without exceeding any operating limits and for assuring that a person in the vicinity of grounded facilities is not exposed to danger of critical electrical shock. Transformer neutral point grounding is for the purpose of controlling the voltage to earth within tolerable limits under a line-to-ground fault. Transformer frame grounding is for the purpose of minimizing the hazardous potential within safety criteria appearing at the faulted equipment. ills paper deeply investigates the grounding resistance effects of distribution power transformers by analysing the neutral to eatth voltages and touch voltages when the fault occurs.

변환행렬법을 이용한 케이블 권선형 배전용 변압기 귄선의 진동모드 해석

This paper proposes a simulation method of the internal winding fault to calculate the short-circuit current, electromagnetic force and vibration mode in a distribution power transformer by using FEM program(FLUX2D) and analytic algorithm. A usage of the Transfer matrix method is also presented for the vibration mode analysis of the cable-type winding of power transformer. The equations of the winding are approximated by the series expansions of the distributed mass mode and Timoshenko`s beam theory. The simulation examples are provided for the cable type winding of the transformer(22.9[kV]/220[V], 1,000[kVA]) to verify the method. The proposed Transfer Matrix Method is also verified by the ANSYS program for the vibration mode of the transformer winding. The method presented may serve as one of the useful tools in the electromagnetic force and vibration analysis of the transformer winding under the short circuit condition.