Extension of Distribution Transformer Life in the Presence of Smart Inverter-based Distributed Solar Photovoltaic Systems

A transformer is an essential but expensive power delivery equipment for a distribution utility.In many distribution utilities worldwide,a sizable percentage of transformers are near the end of their designed life.At the same time,distribution utilities are adopting smart inverter-based distributed solar photovoltaic(SPV)systems to maximize renewable generation.The central objective of this paper is to propose a methodology to quantify the effect of smart inverter-based distributed SPV systems on the aging of distribution transformers.The proposed method is first tested on a modified IEEE-123 node distribution feeder.After that,the procedure is applied to a practical distribution system,i.e.,the Indian Institute of Technology(IIT)Roorkee campus,India.The transformer aging models,alongside advanced control functionalities of grid-tied smart inverter-based SPV systems,are implemented in MATLAB.The open-source simulation tool(OpenDSS)is used to model distribution networks.To analyze effectiveness of various inverter functionalities,time-series simulations are performed using exponential load models,considering daily load curves from multiple seasons,load types,current harmonics,etc.Findings show replacing a traditional inverter with a smart inverter-based SPV system can enable local reactive power generation and may extend the life of a distribution transformer.Simulation results demonstrate,simply by incorporating smart inverter-based SPV systems,transformer aging is reduced by 15%to 22%in comparison to SPV systems operating with traditional inverters.

Design of Non-contact On-load Automatic Regulating Voltage Transformer

At present, an automatic-mechanic contact tap-changer is widely used in power system, but it can not frequently operate. In addition, arc will occur when the switch changes. In order to solve these two problems, this paper presented an automatic on-load voltage-regulating distributing transformer which employed non-contact solid-state relay as tap-changer, and mainly introduced its structure, basic principal, design method of each key link and experimental results. Laboratory simulation experiments informed that the scheme was feasible. It was a smooth and effective experiment device, which was practical in application.

A modified lumped parameter model of distribution transformer winding

The modelling of the distribution transformer winding is the starting point and serves as important basis for the transformer characteristics analysis and the lightning pulse response prediction.A distributed parameters model can depict the winding characteristics accurately,but it requires complex calculations.Lumped parameter model requires less calculations,but its applicable frequency range is not wide.This paper studies the amplitude-frequency characteristics of the lightning wave,compares the transformer modelling methods and finally proposes a modified lumped parameter model,based on the above comparison.The proposed model minimizes the errors provoked by the lumped parameter approximation,and the hyperbolic functions of the distributed parameter model.By this modification it becomes possible to accurately describe the winding characteristics and rapidly obtain the node voltage response.The proposed model can provide theoretical and experimental support to lightning protection of the distribution transformer.

Empirical Thermal Investigation of Oil-Immersed Distribution Transformer under Various Loading Conditions

The distribution transformer is the mainstay of the power system.Its internal temperature study is desirable for its safe operation in the power system.The purpose of the present study is to determine direct comprehensive thermal distribution in the distribution transformers for different loading conditions.To achieve this goal,the temperature distribution in the oil,core,and windings are studied at each loading.An experimental study is performed with a 10/0.38 kV,10 kVA oil–immersed transformer equipped with forty–two PT100 sensors(PTs)for temperature measurement installed inside during its manufacturing process.All possible locations for the hottest spot temperature(HST)are considered that made by finite element analysis(FEA)simulation and losses calculations.A resistive load is made to achieve 80%to 120%loading of the test transformer for this experiment.Working temperature is measured in each part of the transformer at all provided loading conditions.It is observed that temperature varies with loading throughout the transformer,and a detailed map of temperature is obtained in the whole test transformer.From these results,the HST stays in the critical section of the primary winding at all loading conditions.This work is helpful to understand the complete internal temperature layout and the location of the HST in distribution transformers.

Investigation on Noise Pollution Comprehensive Treatment of Distribution Transformer in Living Area

In the current paper,which deals with the noise pollution excited by distribution transformers in the living area,a comprehensive treatment scheme is put forward for the purpose of reducing the sound pressure level emitting into the environment.In accordance with the associated test standard,the sound pressure levels of distribution transformer and surrounding environment are not only tested but analyzed as well.The measurements were carried out with the frequency analysis of the 1/3 octave resolution,with the center frequencies at 125 Hz,250 Hz,400 Hz,and 500 Hz.As illustrated,on the basis of the measurement results,the frequency of noise at 500 Hz of distribution transformer causes the major noise pollution in the surrounding environment.This measurement result is in line with the noise frequency characteristics of distribution transformer.There are two transmission routes of noise:(i)the noise excited by distribution transformer transmits by means of the wall of distribution room,and (ii)part of noise spreads through the ground of distribution room.Accordingly,acoustic shield and vibration isolation device are applied for the reduction of the low frequency noise emitted through the above two paths.Aimed at applying the appropriate acoustic material and vibration mounting,the evaluation of the noise reduction and vibration absorption is carried out in accordance with the sound and vibration insulation theory.Following the noise treatment,the transformer and environment noise are measured again.The corresponding findings shed light on the fact that the sound level satisfied the requirement of limits of the ordinance.The proposed noise treatment scheme can be applied to the existing power distribution facilities for controlling the sound levels that reach a point where it is comparatively more unobjectionable.

Low-loss B18R065 and B20R070 grain oriented electrical steels for grade 1 energy efficiency distribution transformers

To reduce distribution transformer losses and carbon dioxide emissions, in recent years, the major countries in the world have issued mandatory standards for high-energy efficiency in distribution transformers. In 2013,China has carried out a new standard GB 20052-2013. To meet the update of the standard and energy efficiency,it is important to enhance the magnetic properties of core materials. The new products B18R065 and B20R070 which are developed by Baosteel, are successfully used for grade 1 energy efficiency distribution transformers. And Baosteel becomes one of the companies which can supply both the 0.20 mm and the 0.18 mm gauge grain oriented electrical steels （GOES） in the world. The development principle, material properties, and transformer performance of B18R065 and B20R070 were introduced,which were expected to be a useful reference for materials selection by transformer manufacturers.

Management of Charging Load of Electric Vehicles for Optimal Capacity Utilisation of Distribution Transformers

A de-centralised load management technique exploiting the flexibility in the charging of Electric Vehicles (EVs) is presented. Two charging regimes are assumed. The Controlled Charging Regime (CCR) between 16:30 hours and 06:00 hours of the next day and the Uncontrolled Charging Regime (UCR) between 06:00 hours and 16:30 hours of the same day. During the CCR, the charging of EVs is coordinated and controlled by means of a wireless two-way communication link between EV Smart Charge Controllers (EVSCCs) at EV owners’ premises and the EV Load Controller (EVLC) at the local LV distribution substation. The EVLC sorts the EVs batteries in ascending order of their states of charge (SoC) and sends command signals for charging to as many EVs as the transformer could allow at that interval based on the condition of the transformer as analysed by the Distribution Transformer Monitor (DTM). A real and typical urban LV area distribution network in Great Britain (GB) is used as the case study. The technique is applied on the LV area when its transformer is carrying the future load demand of the area on a typical winter weekday in the year 2050. To achieve the load management, load demand of the LV area network is decomposed into Non-EV load and EV load. The load on the transformer is managed by varying the EV load in an optimisation objective function which maximises the capacity utilisation of the transformer subject to operational constraints and non-disruption of daily trips of EV owners. Results show that with the proposed load management technique, LV distribution networks could accommodate high uptake of EVs without compromising the useful normal life expectancy of distribution transformers before the need for capacity reinforcement.

Effect of Climate Change on Transformers Loading Conditions in the Future Smart Grid Environment

The steady-state calculations are performed using IEC guidelines to determine the hot spot temperatures of distribution and power transformers in the worst projected Finnish environment due to long summer periods. Moreover, the effect of increase in winding resistance due to increase in ambient temperatures has been taken into account. The primary objective of the research is to investigate the possible extreme circumstances due to climate change. It is concluded that the power and distribution transformers should be progressively de-rated under such circumstances for their safe operations, which will not only prove cost-effective for utilities but also improve the reliability of the power supply to their valued customers in the challenging future smart grid environment.

The Mandatory Energy Efficiency Standard for Distribution Transformer soon Publicized in China

Owning to the rapid economy development in China and sharp increase of energy consumption in recent years, energy shortage is increasingly apparent and becoming an important obstacle to the sustainable development of our economy. With the aim to relieve the problem of energy shortage, the State Development and Reform Commission places the great emphasis of energy-saving work on improving energy efficiency of industrial energy-consuming products in energy-saving work. The General Administration of Quality Supervision, Inspection and Quarantine of the People’s Republic of China(AQSIQ) has issued and implemented two energy efficiency standards for three-phase induction motors and displacement air compressor, and will soon issue another two energy efficiency standards for clean- water centrifugal pumps and ventilation fans. The transformer is a kind of electric equipment widely used in many industries in national economy, with features of great amount of use, long period of operation and tremendous potential of energy-saving. So, it is necessary to develop the standard of energy efficiency for distribution transformers.It has been an issue of common concern for all countries in the world to reduce the consumption of transformers and upgrade their distribution efficiency.

A NOVEL METHOD FOR ESTIMATING THE SNR OF UNKNOWN EMITTER SIGNAL

It is important to estimate the Signal-to-Noise Ratio(SNR) of unknown emitter signal accurately.In order to resolve the disadvantages of present algorithm,a novel method is proposed in this letter.We extract and normalize the information of zero frequency of received signal by the Wigner-Vile Distribution(WVD) transformation and then get the approximate power of original signal by mathematic transformation,at last,we get the estimate value of SNR by the known account formula of SNR.Simulation results show that it is correct and feasible.

On the generalized Cauchy function and new Conjecture on its exterior singularities

This article studies on Cauchy’s function f （z） and its integral, （2πi）J[ f （z）] ≡ ■C f （t）dt/（t z） taken along a closed simple contour C, in regard to their comprehensive properties over the entire z = x ＋ iy plane consisted of the simply connected open domain D ＋ bounded by C and the open domain D outside C. （1） With f （z） assumed to be C n （n ∞-times continuously differentiable） z ∈ D ＋ and in a neighborhood of C, f （z） and its derivatives f （n） （z） are proved uniformly continuous in the closed domain D ＋ = [D ＋ ＋ C]. （2） Cauchy’s integral formulas and their derivatives z ∈ D ＋ （or z ∈ D ） are proved to converge uniformly in D ＋ （or in D = [D ＋C]）, respectively, thereby rendering the integral formulas valid over the entire z-plane. （3） The same claims （as for f （z） and J[ f （z）]） are shown extended to hold for the complement function F（z）, defined to be C n z ∈ D and about C. （4） The uniform convergence theorems for f （z） and F（z） shown for arbitrary contour C are adapted to find special domains in the upper or lower half z-planes and those inside and outside the unit circle ｜z｜ = 1 such that the four general- ized Hilbert-type integral transforms are proved. （5） Further, the singularity distribution of f （z） in D is elucidated by considering the direct problem exemplified with several typ- ical singularities prescribed in D . （6） A comparative study is made between generalized integral formulas and Plemelj’s formulas on their differing basic properties. （7） Physical sig- nificances of these formulas are illustrated with applicationsto nonlinear airfoil theory. （8） Finally, an unsolved inverse problem to determine all the singularities of Cauchy function f （z） in domain D , based on the continuous numerical value of f （z） z ∈ D ＋ = [D ＋ ＋ C], is presented for resolution as a conjecture.

Fuzzy Logic-based Management of Hybrid Distribution Transformers Using LoRa Technology

Hybrid distribution transformers(HDTs)have better performance than traditional distribution transformers in improving power quality through reducing harmonics,unbalance,voltage fluctuations and low power factors in future smart power distribution systems.In order to increase the service life and reliability of hybrid distribution transformers,this paper proposes a remote management system using LoRa technology based on fuzzy logic.HDT based on a fuzzy logic judgment system(FLJS)replaces the Boolean logic with fuzzy logic and several power quality problems including power factors,load-side current harmonics and voltage unbalance are considered,as well as grid-side voltage deviation and unbalance.This management system can dynamically adjust the working states of HDT according to the output results of the FLJS to reduce the use time of power electronic devices.Due to the application of LoRa,this management system can remotely adjust the parameters of the FLJS in real time for different distribution network nodes to avoid frequent switching of HDT working states.In addition,it is able to remotely monitor the real-time working states and fault states of HDT to reduce recovery time and maintenance costs in case of HDT failure.Finally,simulation and experimental results are presented to verify the effectiveness of the proposed management system for HDT.

Power Flow Model for Medium-voltage Distribution Systems Considering Measurement and Structure Characteristics

Medium-voltage distribution systems(MVDSs)mainly consist of a feeder head,lines,distribution transformers,and the equivalent load or power supply interfaced with the distribution transformers.The information of such load or power supply can be measured via the three-wattmeter method(THM)and the two-wattmeter method(TWM).The measurements can be used to perform the control of the power supply and simulate the characteristics of the load,so the models of the load and the power supply need to consider the measurement characteristics.Existing research works on three-phase power flow(PF)just consider the measurement characteristics of THM.Hence,the PF equation of the bus measured via TWM is firstly built.Based on conventional measurements,an accurate and general model of the grounded and ungrounded slack bus is proposed.Furthermore,the influence arising from the connection type and angle shift of distribution transformers on the admittance matrix is considered,and thus a general three-phase transformer model is summarized,which is applicable for all the transformers mentioned herein.Finally,Newton's method is adopted to solve the PF calculation,and the performance of the proposed PF model is demonstrated through designed tests.

Distribution-Transformed Network for Impulse Noise Removal

This work aims to explore the restoration of images corrupted by impulse noise via distribution-transformed network (DTN), which utilizes convolutional neural network to learn pixel-distribution features from noisy images. Compared with the traditional median-based algorithms, it avoids the complicated pre-processing procedure and directly tackles the original image. Additionally, different from the traditional methods utilizing the spatial neighbor information around the pixels or patches and optimizing in an iterative manner, this work turns to capture the pixel-level distribution information by means of wide and transformed network learning. DTN fits the distribution at pixel-level with larger receptions and more channels. Furthermore, DTN utilities a residual block without batch normalization layer to generate a good estimate. In terms of edge preservation and noise suppression, the proposed DTN consistently achieves significantly superior performance than current state-of-the-art methods, particularly at extreme noise densities.

Relationship between Tissue Distributions of Modified Wuzi Yanzong Prescription(加味五子衍宗方) in Rats and Meridian Tropism Theory

Objective： To investigate the relationship between tissue distributions of modified Wuzi Yanzong prescription（加味五子衍宗方, MWP） in rats and meridian tropism theory. Methods： A high-performance liquid chromatography with Fourier transform-mass spectrometry（HPLC-FT） method was used to identify the metabolites of MWP in different tissues of rats after continued oral administration of MWP for 7 days. The relationship between MWP and meridian tropism theory was studied according to the tissue distributions of the metabolites of MWP in rats and the relevant literature. Results： Nineteen metabolites, mainly flavanoid compounds, were detected in the different rat tissues and classified to each herb in MWP. Further, it was able to establish that the tissue distributions of the metabolites of MWP were consistent with the descriptions of meridian tropism of MWP available in literature, this result might be useful in clarifying the mechanism of MWP on meridian tropism. In the long run, these data might provide scientific evidence of the meridian tropism theory to further promote the reasonable, effective utilization, and modernization of Chinese medicine. Conclusion： The tissue distributions of MWP in vivo were consistent with the descriptions of meridian tropism of MWP.

Performance evaluation of natural esters and dielectric correlation assessment using artificial neural network(ANN)

The performance of correlation between the dielectric parameters of Baobab Oil(BAO)and Mongongo Oil(MGO)is evaluated using Artificial Neural Network(ANN).The BAO and MGO naturally own high Unsaturated Fatty Acids(UFAs)and are highly biodegradable.The temperature studies and dielectric studies are carried out and found that the Natural Esters(NEs)show a reliable performance over mineral oil-based Transformer Oil(TO).Further the endurance test,Partial Discharge Inception Voltage(PDIV)repetition rate and drop after 30 days,dielectric measurements are done as per the standards of IEC(International Electrotechnical Commission)and ASTM(American Society for Testing and Materials).The NEs show stable performance under PDIV and show minimum repetition rate when compared to the TO.The C10H22 or Kerosene(KER)and NEs mixture prove that the NE-based transformer fluids show lesser tendency to hydro peroxidation.The C10H22 acts as a thinning agent and reduces the ageing rate of the NEs,and this leads to slower rate of water saturation.This in turn increases the thermal conductivity of the oil and nearly a 30-days thermal ageing of the oil samples at 90°C shows better strength of liquid insulation.The performance of association between the dielectric properties like breakdown voltage and water content,dissipation factor and thermal conduc-tivity prove that the NEs show consistent performance and is a better substitute for the mineral oil-based TO.