Abstract:Most reasons causing the onload tap changer(OLTC) unfunctional are mechanical faults. In order to ensure the reliable operation of the OLTC, a kind of vibration feature extraction method of OLTC based on the empirical mode decompositionpower spectral density(EMDPSD) algorithm is proposed. Firstly, several mechanical faults of the OLTC is simulated and the vibration signal is collected. The noise of vibration signal is eliminated by the wavelet packet firstly. And then a reasonable order for noise reduction is selected according to the singular entropy which is to eliminate the noise of vibration signal by singular value decomposition(SVD). Secondly, the noisereduced signals are decomposed by EMD and the power spectral density of the IMF is obtained. Finally, the PSD energy is used to construct the eigenvectors. It is shown that the signaltonoise ratio of the vibration signal can be improved by selecting the SVD order of noise reduction based on the singular entropy. Based on the combination of EMD and PSD methods, the fault features of the OLTC can be effectively extracted.

Abstract:Aiming at the shortcomings of traditional data aggregation scheme of power transmission and transformation equipment, such as waste of storage and calculation resources and incomplete data model, a panoramic information aggregation method for transmission and transformation equipment (TTE) based on CIM and REST is designed in this paper. Firstly, CIM defined in IEC 61970/968 is selected as the global model of TTE data, and modeling ideas of online and offline data are given respectively, which makes the data model more complete and unified. Secondly, a data aggregation mechanism based on REST is proposed to solve the problem of resource waste and improve maintenance efficiency and scalability of data platform. Finally, based on CIM model and REST aggregation mechanism, a panoramic information aggregation platform for TTE is established, and the practical application results are introduced in detail to provide a novel idea about equipment data aggregation.

Abstract:The traditional PI control of AC signal results a certain steady state error commonly. Under this background, a new strategy is proposed based on the fuzzy PCI control which is in parallel with a PR control. It controls the gridconnect process of the threephase inverter directly. The fuzzy PCI control can eliminate the steadystate error under given conditions and track AC control variables accurately. The PCI proportional coefficients and ratio coefficient are adjusted online according to error and error rate. In view of the advantage PR control which has an infinite gain at the resonant frequency, the PR control is added to make the system meet the requirements of the gridconnected. The proposed compound control strategy can be utilized to control the AC signal and can be directly applied to the threephase ABC coordinate system without a coordinate change. The cost of the inverter control system is saved. Lately, a model of gridconnected inverter with LC filter is established on MATLAB/Simulink and the feasibility of the strategy is verified.

Abstract:Onload tap changers(OLTC)and capacitor banks have been widely utilized to deal with the problem of voltage violation in lowvoltage(LV)distribution networks with highpenetration photovoltaic(PV). Different control strategies would directly affect the node voltage and operation number of OLTC tap and capacitor bank. In order to seek a suitable control strategy for handling the voltage violation problem in LV distribution network, a power controlbased(PCB)voltage control strategy is proposed on the basis of the analysis of the influence of OLTC reference voltage on the voltage control strategy and the voltage sensitivity matrix theory. In order to consider the influence of time sequence and randomness on PV output and load, probabilistic power flow based on sequential Monte Carlo simulation is utilized to calculate the probability values of network active power loss and node voltage violation probability. The proposed method is compared with the time controlbased(TCB)strategy in the test case. It is shown that the TCB based on the power control not only reduce the node voltage violation probability effectively, but also effectively reduce the action times of taps and capacitor banks, reduce the active power loss, and improve the ability of lowvoltage distribution network to absorb highpermeability household photovoltaic power generation.

Abstract:Distributed generation (DG) and electric vehicle (EV) are the key parts of sustainable development under the lowcarbon background. In order to reduce the negative impact of DG output and electric vehicle charging load volatility on the distribution network, a distributed energy storage system (DESS) is introduced in the planning stage to establish a coordinated and optimized configuration model of DG, DESS and electric vehicle charging stations(EVCS). By introducing the carbon emission reduction index, a multiobjective function is established. The comprehensive income of the distribution network, carbon emission reduction, voltage quality index, comprehensive net load fluctuation index and network loss are considered. Then, the particle swarmharmony search hybrid algorithm is applied to solve the model. Lastly, an IEEE 33bus power distribution system is simulated, it is shown that the established "generationstorageload" joint planning model can effectively reduce system carbon emissions and network losses, and also improve voltage quality and load fluctuation indicators.

Abstract:A large number of electric vehicles are connected to residential communities, putting pressure on power distribution facilities in residential communities. Studying the charging mode of electric vehicles in residential quarters and establishing a monitoring system are the basis for ensuring the friendly interaction between electric vehicles and the power grid. This paper establishes an orderly charging control system for residential quarters based on the monitoring of electric vehicle charging piles. Considering the load characteristics and peak/valley electricity prices of residential quarters, a twostage orderly charging control model for electric vehicles is established to realize the objective of minimizing the charging cost of users and the load peakvalley difference in the residential area. A case study of actual system is studied. It is shown that the method is effective, and it can also operate effectively during the peak/valley electricity price periods, which further verifies the rationality of the ideas and methods proposed in this paper.

Abstract:Under the premise of studying the charging demand of electric vehicle users, two different charging methods are simulated and analyzed by the Monte Carlo method. Firstly, the influence of user responsiveness on the orderly charging of electric vehicles is analyzed, and also the model of analyzing the influences of peaktovalley timeofuse electricity price on electric vehicle load is established. Then, on the basis of simulating the disordered charging load of the electric vehicle, the model is verified by an actual case. The multiobjective optimization genetic algorithm is used to solve the problem, and the effectiveness of using peaktovalley timeofuse electricity price to optimal the grid load is verified.

Abstract:As one of the important devices of the flexible AC transmission system (FACTS), the static var compensator (SVC) helps to improve the stable operation of the power system. By analyzing the generator rotor equation, it can be obtained that the conventional constant voltage control of SVC can not play the role of restraining the oscillation of the damping system. After the additional damping control is adopted, the dynamic stability of the system is obviously improved. This paper designs a SVCbased power oscillation damping (POD) controller, which uses the PSO optimization algorithm to adaptively optimize the controller parameters, and selects the appropriate damping control input signal to compensate the control signal. This paper uses simulink simulation software to establish a HeffronPhilips system model including SVC. Based on this model, the performance of the proposed method is studied in detail, verified by timedomain simulation method, and compared with the traditional power system stabilizer (PSS) controller to show the superiority of the designed controller.

Abstract:With the rapid development of the distributed resources, the operation mode of power distribution network is becoming more and more diversified. The traditional nonlinear ACbased programming model has many lacks in the aspect of calculation. With the rapid development of the distributed resources, the operation mode of power distribution network is becoming more and more diversified. The traditional nonlinear ACbased programming model is lack in the aspect of calculation. In view of this, this paper presents an active power distribution network planning model based on linearized constraints. Firstly, the basic principle and analysis method of distribution network model linearization are presented from two aspects, the power flow linearization and the distribution network connectivity linearization. By analyzing the objective function and constraint conditions of distribution network planning, a mixed integer linear rule (MILP) model is further proposed, which can be solved by a general mathematical optimization toolkit. Finally, simulations under different conditions are carried out and the linearization planning model of distribution network are compared with the nonlinear programming model. It is shown that the proposed method is feasible and effective and a new method is provided for the future planning and operation research of the active distribution network.

Abstract:The transmission conductor and charged structure at the bottom of insulator string tend to be close to the transmission tower due to the effect of wind deviation. The discharge and tripout may occur once the distance between them is less than the minimum air gap value. Therefore, the wind deviation of insulator string threaten the safe operation of power grid seriously and may lead to an enormous economic loss. Under the circumstance, this paper designs and develops a fiber Bragg grating (FBG) tilt sensor. In this sensor, the gravity hammer is fastened on the free end of equal strength cantilever beam which have one FGB pasted on the central symmetrical lines of both sides. The developed inclination sensor is packaged and then installed on the top of the insulator string together with the fiber Bragg grating load cell by the pattern of hoop clamp combination. The insulator string on 30# Tower of an 110 kV transmission line in the Yunnan Power Grid is monitored by the installed device. By combinatory analyzing the monitoring data and wind data, the variation characteristics of windage angle with wind speed are obtained. The nonelectric measuring of fiber Bragg grating tilt sensor provides a reference for safe operation of power transmission line.

Abstract:The multiterminal DC distribution network not only has a large number of nodes, but also contains more power electronic devices. Limited by the processing capacity of a single simulator, it is difficult to realize the realtime simulation of the multiterminal DC distribution network. In order to realize realtime simulation of multiterminal DC distribution network, the ideal transformer model method is utilized to model the multiterminal DC distribution network. The DC grid is considered as the boundary, and the converter stations and their AC systems are treated as a subsystem. The subsystems exchange data through ideal transformer model. Finally, a 5terminal DC distribution network is taken as an example and the system is divided into five subsystems. The dynamic responses in different cases of segmented method are compared with the original integral model then. The dynamic responses of the two kinds of models are nearly the same. The feasibility and effectiveness of the proposed model segmentation method is verified.

Abstract:The power collection and integration system of medium voltage DC in the large PV is more efficient than the traditional AC collection system, which is the potential area to develop the photovoltaic resources in the future. As one of the key components of power collection and integration system with medium voltage DC, DC transformer is analyzed in detail in this paper, including the technical requirements, structure and control method from the collection system. Then, the corresponding fault clearance methods are proposed when the short circuit fault happens in the low voltage or high voltage side. Finally, a simulation for fault operation analysis of DC transformer is included to verify the feasibility and effectiveness of the proposed method.

Abstract:During the AC voltage withstand test, the voltage along the long distance submarine cable would be increased due to the capacitance effect. The elevated voltage value is related to the cable length and the test power supply frequency. Under extreme conditions, this value might threaten the withstand voltage level of cable and hinder voltage withstand test. In this paper, a distributed parameter equivalent circuit model considering cable sheath is established to study the cable terminal voltage. Based on this model, the calculation formula of the voltage along a single core cable is obtained. Then the obtained formula is verified by a simulation. Furthermore, the relationship among the voltage along the cable, the cable length and the power frequency is explored. Research results indicate that, the influence degree of test voltage frequency on the voltage along cable increases with the increasing cable length. Finally, a new frequency scope limitation of withstand test source is proposed for the 220 kV crosslinking polyethylene cable with different lengths to restrict the terminal voltage amplitude. It provides some guidance to field test designers.

Abstract:The identification of characteristic parameters of voltage sag is a prerequisite for evaluating the severity of voltage sag and analyzing its impact on equipment. In this paper, a complex voltage sags parameter identification method is proposed, which combines phase space reconstruction and atomic decomposition. Firstly, it reconstructs the phase space of the voltage sag disturbance sequence, divides the disturbance waveform into segments according to the phase trajectory characteristics of the sag signal, and determines the start and end time of the disturbance section. Then the method builds a sineweight atom library, makes full use of the waveform segmentation results, realizes the orderly matching of atomic parameters in a specific way, and obtains the characteristic parameters of each segment of the voltage sag waveform. Thereby the number of atomic matching parameters and the search range is reduced as well as the computational load of the atomic decomposition algorithm to ensure the accuracy of the algorithm. The results of the calculation example show that the method can accurately extract the characteristic parameters of the voltage sag signal.

Abstract:Characteristics analysis of wind power prediction error can provide more accurate reference for optimal dispatch and stable operation of power system. This paper proposes the mixed t Locationscale distribution model to describe the probability distribution of wind power prediction error characteristics quantitatively. Then it uses improved Kmeans clustering algorithm to determine the model parameters. The distribution characteristics of the ultrashortterm prediction errors of wind power under different prediction methods are validated and analyzed with the measured data of a wind farm. Based on the measured data of the wind farm, we predict and analyze the errors produced by the two prediction models of time series and support vector machines, respectively. It is verified that the model can effectively describe the probability distribution of prediction errors.

Abstract:By extracting the iron cap and disc surface temperature information of the disc suspended porcelain insulator string in the singleframe infrared image, the relative temperature difference is considered as a criterion to diagnose the deterioration state, which is an efficient and accurate method for online automatic monitoring of the insulator string state. In order to accurately extract the temperature information, this paper proposes an algorithm that combines the characteristics of the insulator image and deep learning to accurately identify the iron cap and disc surface area of the porcelain insulator string in the infrared image. The algorithm uses a large number of different parts of insulator images as sample data sets, and is trained by selfconstructed CNN to form three classifiers. Then it uses the classifiers to identify in the corrected insulator string region image and finally utilizes different colors to mark in the original infrared image. It is shown that this algorithm can obtain excellent recognition results of cap and disc area for insulator strings of different voltage levels and different disc types.

Abstract:With the continuous advancement of line loss lean management, the accuracy of transmission line loss calculations is becoming more and more important. The current line loss calculation method does not consider the load level, clock accuracy, and the influence of the metering device, resulting in a large difference between the actual statistics and the calculated results. It is not conducive to the lean development of line loss management. Based on the existing theoretical line loss calculation method, this paper analyzes the statistical line loss influence amount, and proposes a multiparameter correction algorithm to improve the accuracy of line loss calculation. The effectiveness of the method is proven by taking the ChongqingEnshi 500 kV ultra high voltage transmission line as a numerical example.

Abstract:The correctness of the virtual loop connection in substation configuration (SCD) files affects the secondary system protection function. The current configuration file is not standardized, its manual verification is not efficient and its result would be influenced by subjective factors and other issues. This paper presents an automatic check method for the intelligent substation virtual circuit based on the intermediate model file. Firstly, a corresponding IMCD file is established for the ICD of each manufacturer's IED, and a standardized model of DOI and DAI is also established according to relevant specifications to solve ICD file nonstandard issues. Then, the KMCD model is constructed through the strictly reviewed SCD file to ensure the correctness of virtual circuit. Finally, the automatic verification of the virtual is realized and the SCD file of a substation is included as an example to verify the feasibility of the proposed method.

Abstract:The Tconnected tower has achieved a good application in the engineering practice. However, it increases the complex degree of electric field distribution around the tower body. In order to obtain the electric field distribution under the Ttower and around the typical working position of tower body, a 110kV doublecircuit AC Tconnected tower is studied in this paper. Firstly, a model consisting of a Ttower body and wires is established by using threedimensional finite element software COMSOL Multiphysics. Then, the electric field distribution around Tconnected tower is studied. The electric field distribution around the location 1.5m above the ground and the electric field intensity of typical working position on tower body are analyzed under the situation of inconsistent and consistent phase sequence arrangement respectively. It is shown that the inconsistent phase sequence arrangement of doublecircuit line corresponds to the greatest influence to the electric field distribution under Tconnected tower. The maximum value of the electric field at 1.5m above the ground appears on the side of the Tconnected line. The electric field intensities of the location under Tconnected tower and the typical working position of tower body are within safe ranges. The calculation results provide references for the Tconnection design of transmission line.

Abstract:The shortcircuit impedances are important technical parameters for a fourwinding induction filtering transformer (FWIFT), which not only affects the steadystate operation and shortcircuit current calculation, but also involves the effect of induction filtering. In this paper, an induction decoupling method is proposed to establish the voltage equation of four winding induction filter transformer. Then, based on the shortcircuit method, the shortcircuit impedance characteristics of four winding induction filter transformer and influences of filter impedance on the shortcircuit impedances are analyzed on the basis of the threephase shortcircuit method. Finally, a shortcircuit experiment is included to verify the correctness of the theory and calculation method. It is shown that the equivalent impedance of the filter winding is zero, which meets the constraints of the inductive filter. Meanwhile, the impedance parameters of the filter have no influences on the shortcircuit impedance.

Abstract:The silicone rubber of composite insulator shed and housing is a kind of polymer organic material. Due to the effect of environmental stress under the longterm operating, aging phenomena such as the color fading, chalking, cracking, brittleness and decline of hydrophobicity will appear on it inevitably. The performance of insulators affects the safe operation of transmission lines directly. The aging of silicone rubber is related to the complex operating environment and the aging resistance ability, and it is represented as the change of key components directly. Therefore, the sampling inspection for composite insulators should be carried out by operating maintenance departments. In this paper, the key components of silicone rubber analysis schemes are proposed and the rubber content is defined. To measure the components of silicone rubber, 13 kinds of flat silicone rubber samples with certain content of siloxane and different content of aluminum hydroxide and white carbon black are prepared. Methods of density and thermos gravimetric analysis are adopted, then the results are fitted by the linear regression. Silicone rubber samples of the shed inner layer from different manufacturers are selected to verify the consistency of the results obtained by the two methods. It is shown that the rubber content of silicone rubber can be calculated by either the density or the remaining mass ratios at the critical turning point of thermal gravimetric (TG) curve. The field or offline analysis can be carried out according to the actual situation. The operating status of composite insulators can be assessed by the proposed schemes conveniently and reliably, then safe operation of transmission line can be promoted.

Abstract:Submarine cable terminal voltage is an important parameter for the implementation of voltage withstand test. In order to assure the safety and effectiveness of the wiring test of the voltage withstand test, the accurate calculation of the cable terminal voltage is particularly critical. A 220 kV submarine cable of a wind power plant in Jiangsu is considered. Firstly, the distribution parameter model is established and the formula for calculating the voltage along the singlephase cable is deduced. Then, the influence of armor layer and other twophase cables is considered. Combined with the equivalent model of capacitance between different layers of threephase cable, an improved calculation model of submarine cable based on the end parallel equivalent capacitor method is proposed to improve the calculation model so that the terminal voltage can be accurately calculated. Besides, the practical calculation equation of the terminal voltage is also verified by the accurate simulation results of PSCAD/EMTDC software, validating that the calculation equation of the terminal voltage for the submarine cable withstand voltage test deduced is accurate and convenient. It is of great significance to ensure the safety of the withstand voltage test connection scheme.

Abstract:Aiming at the abnormal phenomenon of negative statistical line loss occurring in some interprovincial ultrahigh voltage (UHV) transmission lines under light load, the influence of ambient temperature on measurement of UHV transmission line is analyzed in this paper. Firstly, the UHV transmission line of NanyangJingmen is taken as an example to establish a mathematical model of the influence of temperature on equivalent dividing capacitance of capacitor voltage transformer (CVT). Then, the relationship between the ambient temperature and the equivalent dividing capacitance of CVT is deduced. In the end, based on the historical temperature data, the influence of ambient temperature on the voltage division ratio of CVT is calculated. It is shown that the error of CVT voltage ratio caused by the environmental temperature may result in the negative statistical line loss of UHV transmission line when considering the discrepancies of CVT parameters.

Abstract:Medium voltage feeders face voltage deviation and fluctuation problems, and there are many choices of governance measures and equipment. A classification and voltage governance measures selection method of medium voltage feeders is proposed in view of the current situation that power grid enterprise is difficult to select the pertinent measures for massive medium voltage feeders in the planning and operation of the network. Firstly, considering the influence of feeder's property parameters on voltage, a voltage characteristic index system is designed which covers the line property and load characteristic. Then, the feeders are sorted by the Fuzzy Cmean (FCM) clustering algorithm based on the factor analysis so as to judge whether the feeders need to be transformed or install the governance equipment. Then, the bus voltage characteristic evaluation method is designed to describe the probability distribution and time domain fluctuation characteristics. The primary clustering results are further refined by the bus voltage characteristic grades to determine whether it is necessary to modify bus voltage control strategy or install equipment on the bus. Finally, the effectiveness and practicability of this method are verified by an example.

Abstract:With the development of the Faulted Feeder Selection Device (FFSD) with the grounding current technology, lots of FFSDs with different principles have been used in the distribution automation system. Most researches focus on examining the actual performance of different FFSDs and then choosing the suitable ones. However, the actual operation performance of these FFSD is not satisfied in practice. On one hand, the test of on line performance is examined offline, so it is hard to find the overall stochastic fault scenarios of power distribution network. On the other hand a valid assessment methodology is absent without entire testing information, the potential drawbacks of distribution network terminal can not be predicted and removed. In order to solve these two problems, this paper firstly establishes a real distribution network model based on the PTDS, which provides various fault scenarios for the faulty line detection. In addition, by using the results of RTDS test from different faulty line detections, an integrated assessment method for the defect of FFSD based on Logistic regression model is put forward. Finally, the blind area of FFSD with different principles is introduced and assessed with the proposed method, which provides a significant reference values for the selection of accessing network equipment.