Power supply arm protection scheme of high-speed railway based on wide-area current differential

When fault occurs on cross-coupling autotransformer(AT)power supply traction network,the up-line and down-line feeder circuit breakers in the traction substation trip at the same time without selectivity,which leads to an extended power failure.Based on equivalent circuit and Kirchhoff’s current law,the feeder current characteristic in the substation,AT station and sectioning post when T-R fault,F-R fault,and T-F fault occur are analyzed and their expressions are obtained.When the traction power supply system is equipped with wide-area protection measurement and control system,the feeder protection device in each station collects the feeder currents in other two stations through the wide-area protection channel and a wide-area current differential protection scheme based on the feeder current characteristic is proposed.When a short-circuit fault occurs in the power supply arm,all the feeder protection devices in each station receive the feeder currents with time stamp in other two stations.After data synchronous processing and logic judgment,the fault line of the power supply arm can be identified and isolated quickly.The simulation result based on MATLAB/Simulink shows that the power supply arm protection scheme based on wide-area current differential has good fault discrimination ability under different fault positions,transition resistances,and fault types.The verification of measured data shows that the novel protection scheme will not be affected by the special working conditions of the electrical multiple unit(EMU),and reliability,selectivity,and rapidity of relay protection are all improved.

Privacy Protection Algorithm for the Internet of Vehicles Based on Local Differential Privacy and Game Model

In recent years,with the continuous advancement of the intelligent process of the Internet of Vehicles(IoV),the problem of privacy leakage in IoV has become increasingly prominent.The research on the privacy protection of the IoV has become the focus of the society.This paper analyzes the advantages and disadvantages of the existing location privacy protection system structure and algorithms,proposes a privacy protection system structure based on untrusted data collection server,and designs a vehicle location acquisition algorithm based on a local differential privacy and game model.The algorithm first meshes the road network space.Then,the dynamic game model is introduced into the game user location privacy protection model and the attacker location semantic inference model,thereby minimizing the possibility of exposing the regional semantic privacy of the k-location set while maximizing the availability of the service.On this basis,a statistical method is designed,which satisfies the local differential privacy of k-location sets and obtains unbiased estimation of traffic density in different regions.Finally,this paper verifies the algorithm based on the data set of mobile vehicles in Shanghai.The experimental results show that the algorithm can guarantee the user’s location privacy and location semantic privacy while satisfying the service quality requirements,and provide better privacy protection and service for the users of the IoV.

Research on the Reason for Transformer Differential Protection Mal-operation Caused by Sympathetic Inrush

The paper is concerned with whether CT transient saturation, which caused by sympathetic inrush, is the direct reason for mal-operation of transformer differential relays. In order to analyze transforming characteristics of saturated CT, the gain of each harmonic current transforming from primary winding to secondary winding of transient saturation CT is calculated. Based on the fact that series sympathetic inrush is easier to lead differential relay mal-operation than parallel sympathetic inrush, the effect of CT saturation on differential relay?in the case of both parallel sympathetic inrush and series sympathetic inrush are investigated respectively. Theory analysis and simulation show that higher harmonic will be transferred by saturated CT more easily than lower harmonic, and then the second harmonic proportion of CT secondary side is higher than that of CT primary side. Thus CT transient saturation itself is not essential reason for differential relay mal-operation. Parallel sympathetic inrush and series sympathetic inrush will lead to different location CT saturated. Parallel sympathetic inrush will lead to CT located system side saturated;second harmonic ratio of differential current increase and dead angle is large. Series sympathetic inrush will lead to CT located load side saturated;second harmonic ratio of differential current decrease and dead angle is small.

Solution Scheme for Time Synchronization of Current Differential Protection between Digital Substations

In digital substations with power transformers, the key to implementation of line differential protection is synchronization of electrical quantities at both two sides. System framework of current differential protection for lines between digital substations is analyzed briefly, as well as the necessity of demand for time synchronization. Principle of time synchronization based on GPS and IEEE1588 PTP (Precision Time Protocol) are introduced. Time synchronization of current differential protection between digital substations based on IEC61850 is discussed. This paper puts forward two solution schemes of time synchronization, analyzes their advantages and disadvantages respectively, and points out that the development direction of time synchronization of differential protection between digital substations is IEEE1588 PTP.

Research on the Differential Protection Algorithm of Multi-Tap Special Transformer

Compared with conventional transformers, the rectiformer is special in connection mode, which is multi-tap and not equipped with the differential protection. In this paper, the differential protection algorithm for Multi-tap special transformer was derived. The regulating methods for the rectiformer were studied first, and then the rectiformer model of one electrolytic aluminium plant was built by PSCAD/EMTDC, characteristics of the rectiformer bank were also analyzed. The algorithm was derived on the basis of the per-unit system, and the processing methods of the regulating transformer’s tap position information were proposed. Finally, a contrast of differential protection algorithm between the multi-tap special transformer and the conventional transformer was made.

Transmission Lines Distance Protection Using Differential Equation Algorithm and Hilbert-Huang Transform

This paper proposed the scheme of transmission lines distance protection based on differential equation algorithms (DEA) and Hilbert-Huang transform (HHT). The measured impedance based on EDA is affected by various factors, such as the distributed capacitance, the transient response characteristics of current transformer and voltage transformer, etc. In order to overcome this problem, the proposed scheme applies HHT to improve the apparent impedance estimated by DEA. Empirical mode decomposition (EMD) is used to decompose the data set from DEA into the intrinsic mode functions (IMF) and the residue. This residue has monotonic trend and is used to evaluate the impedance of faulty line. Simulation results show that the proposed scheme improves significantly the accuracy of the estimated impedance.

Study on the Effect of Multi-Type Current Transformers Hybrid Operation on Differential Protection of the Bus Based on Dynamic Simulation

This paper analyzes characteristics of multi type current transformers hybrid operation for each branch of the bus and their effects on differential protection of the bus. By theoretically analyzing transmission characteristics of multi type current transformers and their influence factors, we study the dynamic model testing method of multi type current transformers for the bus, and design 3 kinds of testing schemes by making the equivalent model based on the field of P-level current transformer, TPY-level current transformer and electronic current transformer, and build the hybrid operation testing platform of multi type current transformers. Finally, we compare and analyze the transmission characteristics difference of multi type current transformers on the same branch and the characteristics difference of hybrid operation in two successive external faults, analyze the cause behind the differences, and put forward the corresponding improvement measures.

High-Impedance Bus Differential Protection Modeling in ATP/MODELS

This paper presents a modeling of a high-impedance bus differential protection logic using the ATP (Alternative Transients Program) MODELS language. The model is validated using ATP simulations on an electrical system consisting of a sectionalized bus arrangement with four transmission lines (TLs) and two autotransformers. The obtained results validate the model and present some of the advantages of using this type of bus protection, such as fast and safe operation, even when under adverse conditions such as current transformers (CTs) magnetic core saturation upon the occurrence of external faults.

XGBoost Algorithm under Differential Privacy Protection

Privacy protection is a hot research topic in information security field.An improved XGBoost algorithm is proposed to protect the privacy in classification tasks.By combining with differential privacy protection,the XGBoost can improve the classification accuracy while protecting privacy information.When using CART regression tree to build a single decision tree,noise is added according to Laplace mechanism.Compared with random forest algorithm,this algorithm can reduce computation cost and prevent overfitting to a certain extent.The experimental results show that the proposed algorithm is more effective than other traditional algorithms while protecting the privacy information in training data.

A Testing Method for Ratio Restraint Characteristics of Differential Relay Protection of Transformers

In this paper, a method to calculate the slope of the ratio restraint characteristic of a transformer differential relay protection is proposed. The method allows using some concise but effective means to get the slope. Modulating the argument of current output from ONLLY testing equipment can make the relay protection device operate, thus, the data used for calculation would be obtained naturally after several trails. In order to make sure how effective that method could be, some experiment data is given as well.

Dynamic shared segment protection algorithm with differentiated reliability in GMPLS networks

To improve the resource utilization ratio and shorten the recovery time of the shared path protection with differentiated reliability （SPP-DiR） algorithm, an algorithm called dynamic shared segment protection with differentiated reliability （DSSP-DiR） is proposed for survivable GMPLS networks. In the proposed algorithm, a primary path is dynamically divided into several segments according to the differentiated reliability requirements of the customers. In the SPP-DiR algorithm, the whole primary path should be protected, while in the DSSP- DiR algorithm, only partial segments on the primary path need to be protected, which can reduce more backup bandwidths than that in the SPP-DiR algorithm. Simulation results show that the DSSP-DiR algorithm achieves higher resource utilization ratio, lower protection failure probability, and shorter recovery time than the SPP-DiR algorithm.

Determination of isolation layer thickness for undersea mine based on differential cubature solution to irregular Mindlin plate

The differential cubature solution to the problem of a Mindlin plate lying on the Winkler foundation with two simply supported edges and two clamped edges was derived.Discrete numerical technology and shape functions were used to ensure that the solution is suitable to irregular shaped plates.Then,the mechanical model and the solution were employed to model the protection layer that isolates the mining stopes from sea water in Sanshandao gold mine,which is the first subsea mine of China.Furthermore,thickness optimizations for the protection layers above each stope were conducted based on the maximum principle stress criterion,and the linear relations between the best protection layer thickness and the stope area under different safety factors were regressed to guide the isolation design.The method presented in this work provides a practical way to quickly design the isolation layer thickness in subsea mining.

Development and Application of Lightning Protection Technologies in Power Grids of China

In recent years,along with the rapid expansion of power grids,the increasing complication of grid structures,and the development of smart grids and energy technologies,the lightning protection of power grids becomes increasingly prominent.Power grids of China have acquired significant achievements on lightning protection technologies,which are reviewed in this paper.A technical route of lightning protection is introduced in detail; it allows us to find problems through detection and measurement of lightning,to analyze problems through evaluation and simulation of lightning,to solve problems through lightning protection measures,and to prevent problems through hazard risk warning of lightning.Following the route,the technical breakthroughs of these four aspects in China are presented,including the chinese lightning detection network(CLDN),natural lightning observations,lightning faults detection at transmission lines,lightning current measurements,progresses in lightning distribution maps,lightning fault replays,lightning hazard risk evaluations,and lightning simulated experiments,as well as novel lightning protection measures.The practical devices and systems corresponding to the technologies mentioned above are also introduced and discussed.Due to the progress of lightning protection technologies in recent years,despite the rapidly growing length of transmission lines in China,the lightning accident rate is controlled at a certain level.

Privacy-Preserving Collaborative Filtering Algorithm Based on Local Differential Privacy

Mobile edge computing(MEC)is an emerging technolohgy that extends cloud computing to the edge of a network.MEC has been applied to a variety of services.Specially,MEC can help to reduce network delay and improve the service quality of recommendation systems.In a MEC-based recommendation system,users’rating data are collected and analyzed by the edge servers.If the servers behave dishonestly or break down,users’privacy may be disclosed.To solve this issue,we design a recommendation framework that applies local differential privacy(LDP)to collaborative filtering.In the proposed framework,users’rating data are perturbed to satisfy LDP and then released to the edge servers.The edge servers perform partial computing task by using the perturbed data.The cloud computing center computes the similarity between items by using the computing results generated by edge servers.We propose a data perturbation method to protect user’s original rating values,where the Harmony mechanism is modified so as to preserve the accuracy of similarity computation.And to enhance the protection of privacy,we propose two methods to protect both users’rating values and rating behaviors.Experimental results on real-world data demonstrate that the proposed methods perform better than existing differentially private recommendation methods.

Complex Percentage Differential Relay

This paper introduces a new complex percentage differential relay for bus protection. It allows greater CT errors during the external fault and is still sensitive to the intemal fault with high fault resistance or out-flowing current.The CTs of the differential circuit of the new relay may have different transformation ratio, so the new relay can share CTs with other relays and don’t need special CTs only for differential protection. It may be applied in transformer differential protection as well.

A Differential Privacy Protection Protocol Based on Location Entropy

A Location-Based Service(LBS)refers to geolocation-based services that bring both convenience and vulnerability.With an increase in the scale and value of data,most existing location privacy protection protocols cannot balance privacy and utility.To solve the revealing problems in LBS,we propose a differential privacy protection protocol based on location entropy.First,we design an algorithm of the best-assisted user selection for constructing anonymity sets.Second,we employ smart contracts to evaluate the credibility of participants,which ensures the honesty of participants.Moreover,we provide a comprehensive experiment;the theoretical analysis and experiments show that the proposed protocol effectively resists background knowledge attacks.Generally,our protocol improves data availability.Particularly,it realizes user-controllable privacy protection,which improves privacy protection and strengthens security.

Sampled Value Attack Detection for Busbar Differential Protection Based on a Negative Selection Immune System

Considering a variety of sampled value(SV)attacks on busbar differential protection(BDP)which poses challenges to conventional learning algorithms,an algorithm to detect SV attacks based on the immune system of negative selection is developed in this paper.The healthy SV data of BDP are defined as self-data composed of spheres of the same size,whereas the SV attack data,i.e.,the nonself data,are preserved in the nonself space covered by spherical detectors of different sizes.To avoid the confusion between busbar faults and SV attacks,a self-shape optimization algorithm is introduced,and the improved self-data are verified through a power-frequency fault-component-based differential protection criterion to avoid false negatives.Based on the difficulty of boundary coverage in traditional negative selection algorithms,a self-data-driven detector generation algorithm is proposed to enhance the detector coverage.A testbed of differential protection for a 110 kV double busbar system is then established.Typical SV attacks of BDP such as amplitude and current phase tampering,fault replays,and the disconnection of the secondary circuits of current transformers are considered,and the delays of differential relay operation caused by detection algorithms are investigated.

DP-ASSGD: Differential Privacy Protection Based on Stochastic Gradient Descent Optimization

Recently,differential privacy algorithms based on deep learning have become increasingly mature.Previous studies provide privacy mostly by adding differential privacy noise to the gradient,but it will reduce the accuracy,and it is difficult to balance privacy and accuracy.In this paper,the DP-ASSGD algo-rithm is proposed to counterpoise privacy and accuracy.The convergence speed is improved,the number of optimized iterations is decreased,and the privacy loss is significantly reduced.On the other hand,by using the postprocessing immunity characteristics of the differential privacy model,the Laplace smoothing mecha-nism is added to make the training process more stable and the generalization ability stronger.The experiment uses the MNIST dataset,with the same privacy budget,and compared with the existing differential privacy algorithms,the accu-racy is improved by 1.8%on average.When achieving the same accuracy,the DP-ASSGD algorithm consumes less privacy budget.