Electric Power Apparatus Research Articles

Energy consumption analysis of power grid distribution transformers based on an improved genetic algorithm

With the promotion of energy transformation, the utilization ratio of electrical power is progressively rising. Since electrical power is challenging to store, real-time production and consumption become imperative, imposing significant demands on the dependability and operational efficiency of electrical power apparatus. Suppose the load distribution among multiple transformers within a transformer network exhibits inequality. In such instances, it will amplify the total energy consumption during the voltage conversion process, and local, long-term high-load transformer networks become more susceptible to failures. In this article, we scrutinize the matter of transformer energy utilization in the context of electricity transmission within grid systems. We propose a methodology grounded on genetic algorithms to optimize transformer energy usage by dynamically redistributing loads among diverse transformers based on their operational status monitoring. In our experimentation, we employed three distinct approaches to enhance energy efficiency. The experimental findings evince that this approach facilitates swifter attainment of the optimal power level and diminishes the overall energy consumption during transformer operation. Moreover, it exhibits a heightened responsiveness to fluctuations in power demand from the electrical grid. Experimental results manifest that this technique can truncate monitoring time by 27% and curtail the overall energy consumption of the distribution transformer network by 11.81%. Lastly, we deliberate upon the potential applications of genetic algorithms in the realm of power equipment management and energy optimization issues.

Preface to Special Issue on “Recent Magnetic Materials and Their Application Technologies on Electrical Power Machinery and Apparatus”

2015年に開催された第21回気候変動枠組条約締約国会議（COP21）において，政府は2030年までに温室効果ガス排出量を2013年度比で26％削減することを内外に公約している。また，2015年に策定されたSDGs（Sustainable Development Goals，持続可能な開発目標）では，「目標13：

電力用SF<sub>6</sub>代替技術の変遷と現状

1．はじめに

News From Japan

Power electronics have been playing a big role in many fields of our daily lives. However, as has been well known, at least among high voltage electrical insulation engineers for these two decades, this situation brings about a drastic increase in the risk of partial discharges (PDs). That is, compared with ac voltages with sinusoidal wave shapes at frequencies of 50 or 60 Hz, voltages fed from or induced by power electronic circuits or devices such as converters and inverters contain much shorter fronts and tails in their waveforms. In addition, such devices generate surge voltages with higher amplitudes. Therefore, as power electronic devices are used more and more widely, PDs could be induced much more frequently. This, in turn, increases the importance of monitoring the occurrence of PDs in electric power apparatus such as transformers and rotating machines like motors and generators. However, it is in general difficult for conventional PD testers to monitor PDs generated by such converter-fed voltages. With this background, ECG Kokusai Co., Ltd., Tokyo, has developed a variety of PD testers. In this short article, two of them are briefly introduced.

Study on degradation diagnostic method for silicone rubber

To evaluate the degradation degree of silicone rubber (SiR) of electric power apparatus arranged for a long period of time in the coastal area, we repeatedly performed a salt fog aging test against SiR specimens. Then, the surface hydrophobicity and the leakage current were evaluated. The results showed that a required time for recovering hydrophobicity and a discharge ignition time until the leakage current is detectable are good indexes for degradation diagnosis. Especially, the required time for recovering hydrophobicity is useful.

Partial Discharge Random Noise Removal Using Hankel Matrix-Based Fast Singular Value Decomposition

The most effective method for insulation assessment in an electrical power apparatus is partial discharge (PD) detection. During measurements, the interference from the background environment hampers the PD signal and reduces its measurement accuracy. This article discusses on the implementation of a Hankel matrix (HM)-based fast singular value decomposition (H-FSVD) technique for removing noise from the PD signals. The data are first represented into HM structure, with appropriate sampling then using the Lanczos process, the HM size is reduced and through singular spectral analysis thresholds are fixed for noise detection and removal. This algorithm has been examined on simulated as well as PD signals measured on two different laboratory environments from transformers with real and simulated noise. The experiment is part of a series of experiments to detect PD patterns related to realistic transformer defects. The denoising performance of H-FSVD is compared with the wavelet-based denoising methods, empirical mode decomposition method, and normal SVD. Numerical results show that H-FSVD efficiently removes the noise with less computation time, even for large size data.

Modeling of the Winding Hot-Spot Temperature in Power Transformers: Case Study of the Low-Loaded Fleet

A proposal of the dynamic thermal rating (DTR) applied and optimized for low-loaded power transformers equipped with on-line hot-spot (HS) measuring systems is presented in the paper. The proposed method concerns the particular population of mid-voltage (MV) to high-voltage (HV) transformers, a case study of the population of over 1500 units with low average load is analyzed. Three representative real-life working units are selected for the method evaluation and verification. Temperatures used for analysis were measured continuously within two years with 1 h steps. Data from 2016 are used to train selected models based on various machine learning (ML) algorithms. Data from 2017 are used to verify the trained models and to validate the method. Accuracy analysis of all applied ML algorithms is discussed and compared to the conventional thermal model. As a result, the best accuracy of the prediction of HS temperatures is yielded by a generalized linear model (GLM) with mean prediction error below 0.71% for winding HS. The proposed method may be implemented as a part of the technical assessment decision support systems and freely adopted for other electrical power apparatus after relevant data are provided for the learning process and as predictors for trained models.

Development and Experimental Evaluation of Leakage Current Measurement Sensor for Electrical Power Apparatus

Abstract Leakage current measurement plays an important role in determining the healthiness of high voltage insulation of a power apparatus. High voltage (HV) insulation degrades due to electrical, thermal and mechanical ageing and their cumulative effects, and thus the leakage current of the insulation increase over a period of time. The accurate and real time measurement of leakage current enables the utilities to on-line access the healthiness of the insulation. This paper describes about the design, development, calibration and testing of a novel non-contact type passive leakage current sensor which can be used for monitoring of various electrical devices based on the analysis of the leakage current captured by the sensor. The developed sensor has been successfully used for measurement of leakage current in oil-filled HV bushings as well as in gas insulated surge arresters. The sensitivity of the developed sensor as per its design can be in the order of few milli amperes in case of bushing and in the order few micro amperes for surge arrester monitoring. The paper also reported a novel design of bushing adapter-sensor assembly for on-line measuring the leakage current in HV bushings without using the conventional capacitive or resistive tapping based measurements. Further, results covering experimental leakage current measurement on a 420 kV bushing using the developed adapter sensor assembly have also been presented. To establish capabilities of the developed sensor with optimized design parameters, laboratory measurements of leakage current on 420 kV and 145 kV GIS surge arresters have also been carried out and reported in the paper. Third harmonic content of surge arrester leakage current has also been estimated in-line with IEC requirement to assess the healthiness of the surge arrester. Finally, suitability of the developed sensor for leakage current measurement of above power apparatus equipment has also been analyzed and discussed.

A review on SF[formula omitted] substitute gases and research status of CF[formula omitted]I gases

SF6 gas is widely used in electric power apparatus as an insulation and arc-quenching medium. However, the application of SF6 gas faces two serious problems, including the heavy global warming effect and high toxicity of its decomposition products. So, scholars committed to finding environmental-friendly alternative to SF6 gas and the relevant research results have been obtained. As an insulating or extinguishing medium, conventional gases, SF6 gas mixtures and electronegative gases and mixed gases exhibit different strengths and disadvantages. The current research progress of the main alternative gas has been summarized in this paper. And that is summarized in detail in terms of physical and chemical properties, insulating properties, arc characteristics, mechanism and the scope and limitations of different alternative gas in engineering applications are analyzed. Meanwhile, we forecast the development prospects of environment-friendly gas insulation, and theoretically analyzed CF3I, which has the potential to replace SF6. Finally, we analyzed the current application feasibility and scope of CF3I, and pointed out the further research direction.

Investigation on Effect of Magnetic Field Dependency Coefficient of Critical Current Density on the AC Magnetizing Loss in HTS Tapes Exposed to External Field

High-temperature superconducting (HTS) technology is the most promising, advanced, and beneficial technological developments of the last two decades in terms of fabricating more efficient, compact, and reliable electrical power apparatus. The second-generation HTS wires are now quite competitive with traditional conductors from the cost point of view. In addition, they are of high interest in electrical machine manufacturing due to their unique merits such as high current density, high magnetic field, and low loss. The most significant issue for any superconducting devices which work with alternating current or magnetic field is the AC loss of the HTS tapes. Since HTS tapes are always exposed to an external magnetic field in electrical machine applications, it is vital to consider the effect of this external field on their AC magnetizing (ACMG) loss. It is well-known that external magnetic field decreases the current carrying capability of the wire. In real life, critical current density of HTS tapes is dependent to magnetic field but this dependency sometime was not considered in modeling stage in order to make it faster and simple. In this paper, the electromagnetic properties of HTS tapes for use in superconducting electric machines have been investigated with a particular focus on the ACMG loss of YBCO tapes. For this purpose, a two-dimensional finite element model has been implemented based on the H formulation in order to study the effect of dependency of critical current density to magnetic field on the variation of ACMG loss. The modeling results will be helpful for electrical machine designers to have a better understanding about this effect and have a more accurate estimate of ACMG loss in design stage.

Comparison of capacitive and inductive sensors designed for partial discharges measurements in electrical power apparatus

In the paper results of simultaneously conducted measurements achieved using capacitive and inductive sensors are presented according to different PD model sources immersed in a mineral transformer insulation oil. All measurements are preceded under laboratory conditions using typical measurement set up commonly applied for on-site PD detection: measuring impedance and capacitor and high frequency current transformer (HFCT) are used respectively. Measuring frequency and voltage level influence as well as phase resolved PD patterns analysis are investigated in the research. Various fundamental PD signal descriptors assigned for selected frequencies are also proposed and compared for chosen sensors. The main purpose of the presented research is to compare PD measurement results achieved using selected type of sensors during laboratory measurements and to point the best application areas in fields of PD detection in high voltage apparatus under normal operating conditions. Furthermore a proper measurement results interpretation coming from different sensors as well as measurement conducting problems and achieved patterns disparities are also discussed in the paper.

Foreword for Special Issue “Onboard Electric Power System and Apparatuses”

Foreword for Special Issue “Onboard Electric Power System and Apparatuses”

「電力・電気機器関連の電磁界数値解析」特集号によせて

「電力・電気機器関連の電磁界数値解析」特集号によせて

電力・電気機器の最適化

1. はじめに

静止器設計への磁界解析の応用

1. はじめに

電力・電気機器関連の電磁界数値解析技術の最新動向

電力・電気機器関連の電磁界数値解析技術の最新動向

Development of the Preventive Diagnosis Algorithm on the Partial Discharges Using Current and Ultrasonic Sensors

In this paper, the development of a novel diagnosis algorithm for partial discharges in electric power apparatus was carried out by current and ultrasonic sensors. 6 models for simulating partial discharge in electric power apparatus were used. It was classified into the training and test procedures, and PCA in dimension reduction and kNN classifier were used for the exact decision on partial discharge faults. The cD3 coefficients through wavelet transform in the feature extraction was best matched with the characteristics of partial discharges. The final results of the developed diagnosis algorithm showed the very high accuracy on each partial discharge faults.

Topics on Polymeric Insulating Materials for Electric Power Apparatus

Topics on Polymeric Insulating Materials for Electric Power Apparatus

Fabrication and simulation of permittivity graded materials for electric field grading of gas insulated power apparatus

An innovation for the higher performance and reliability of electric power apparatus can be brought about by a novel technique on electrical insulating materials. The application of functionally graded materials (FGM) with spatial distribution of dielectric permittivity in solid insulator is an effective technique to contribute to the above innovation, because FGM can control the electric field distribution with a simple shape. In this paper, we investigated the fabrication and simulation techniques of FGM with various spatial distributions of dielectric permittivity using centrifugal force. Firstly, we developed a simulation technique to estimate the dielectric permittivity distribution of FGM by considering the particle movement in a viscous fluid under centrifugal force. Secondly, based on the simulation technique, we fabricated FGM samples with various relative permittivity distribution and confirmed the validity of the simulation technique. Consequently, the fabrication results provided a good agreement with the simulation results.

Analysis of the insulation characteristics of C3F8 gas mixtures with N2 and CO2 using boltzmann equation method

This paper studied the insulation characteristics of C3F8 gas mixtures with N2 and CO2 from the point view of electron swarm parameters. The density-normalized effective ionization coefficient (α-η)/N and electron drift velocity Ve in binary C3F8-N2 and C3F8- CO2 gas mixtures are calculated by solving the Boltzmann equation in the condition of steady-state Townsend discharge experiment. Values of the limiting electric field strength for which the electron ionization exactly balances the attachment are derived from the effective ionization coefficient data. It is found that the limiting field strength of C3F8-N2 gas mixture is greater than that of C3F8-CO2 for C3F8 gas content k varied from 0% to 100%, and the C3F8-N2 gas mixture containing 20% proportion C3F8 can achieve 60% dielectric strength of pure C3F8. Additionally, the synergistic effects of the insulation strength for C3F8 gas mixtures are also evaluated and compared with that of SF6-N2 mixture. The calculation results, together with the discussions on liquefaction temperature and global warming potential indicate that gas mixtures containing C3F8 are feasible for applying in electric power apparatus as insulation medium.