Digital simulation studies on long transmission line protection based on balance of energy

The protection based balance of energy is a new technique specially proposed for long transmission lines. This technique depends upon the calculation of net energy into the transmission line by two independent methods and comparing them to indicate healthy and faulty conditions. In order to study the performance and feasibility of the protection based on balance of energy, the new protection has been extensively tested by using EMTP on a long transmission line with various configurations and operating conditions (including single pole line, double circuit lines and two phase operation). The results calculated by EMTP show that under any condition of a power system, the proposed technique has excellent performance,the viability even for high resistance ground faults and a short operation time.

Impact of Sensor Technology for Line Protection Performance

The paper has presented the impact on the line protection performance with the introduction of MUs （merging units） in the process bus level. The paper begins with the introduction on modem digital substation structure and process bus. Then, the paper describes the performances of different sensors such as CTs （current transformers）, CVTs （capacitive voltage transformers）, FOCS （fiber optical current transducers） and FOVS （fiber optical voltage transducers）. With the use of above transducers together with MUs, the performance of distance protection function and line differential protection function have been investigated and presented. Finally, conclusions based on the study are presented in the paper.

Transmission line protection challenges influenced by inverter-based resources:a review

High penetration of renewable energy sources(RES)leads to new challenges for protection devices.Protection schemes are typically designed according to the dynamic behavior of rotating machines as generation sources,while the RES dynamic response,mainly governed by inverters,is not considered.Consequently,some relevant algorithms of transmission line protection are experiencing challenges because of the fact that magnitude and phase angle com-parison,amount of negative-sequence,and short-circuit current level are affected by the RES.Therefore,an in-depth study of this issue is necessary,one which considers the main causes and new methodological criteria solutions.This work presents an extensive literature review of the evaluation of electrical protection performance and the effects of RES connected to a power grid through inverters.Bibliographic data on many representative publications related to this topic are obtained to show the current research lines and their proposed solutions.In addition,this work identi-fies the main protection functions affected and describes the new protection schemes that consider RES.Finally,an analysis and discussion of the selected bibliography are presented.

Game Analysis and Mechanism Design of Ecological Protection Red Line for Ecologically Vulnerable Areas in Western China

Drawing the ecological protection red line is to maintain the integrity and benign operation of the ecosystem within the area,and to ensure that the ecological environment is within the boundary of controllable ecological security.Taking the ecologically vulnerable areas in western China as the research object and using the game theory and literature analysis,this paper studied the game behavior of ecological protection red line in these areas.In addition,this paper also analyzed the stakeholders such as government,enterprises and the masses in the drawing of the ecological protection red line,and comprehensively analyzed the game strategies between the government and the masses,the government and enterprises,and the central and local governments and enterprises.On the basis of the analysis,it came up with a safeguard mechanism for the coordination of the interests of the ecological protection red line.

Study on the Delineation of Ecological Protection Red Line in Ecological Fragile Region of the West

Ecological protection red line is one of the main contents in system construction of ecological civilization in China, and also reflects the trend and the will of the national eco-environment protection system reform. In this paper, taking ecological fragile area of the west as the research object, and using literature analysis, comparative analysis and other methods, the characteristics in ecological fragile area of the west are compre-hensively elaborated, and the relationship between ecological vulnerability and ecological protection red line is clarified, and the delineation theory and methods of ecological protection red line are analyzed, such as ecological suitability analysis, regional ecological security pattern and DPSIR model. Finally, key issues of ecological protection red line delineation in ecological fragile zone of the west are proposed.

Line Differential Protection Scheme Modelling for Underground 420 kV Cable Systems

Based on the analysis of a specific relay model and an HVAC （high voltage alternating current） cable system, a detailed approach to EMTDC/PSCAD modelling of protective relays is presented. Such approach allows to create complex and accurate relay models derived from the original algorithms. Relay models can be applied with various systems, allowing to obtain the most optimal configuration of the protective relaying. The present paper describes modelling methodology on the basis of Siemens SIPROTEC 4 7SD522/610. Relay model was verified experimentally with its real equivalent by both EMTP-simulated and real world generated current signals connected to the relay.

Fault Location in Transmission Lines Using BP Neural Network Trained with PSO Algorithm

In modem protection relays, the accurate and fast fault location is an essential task for transmission line protection from the point of service restoration and reliability. The applications of neural networks based fault location techniques to transmission line are available in many papers. However, almost all the studies have so far employed the FNN （feed-forward neural network） trained with back-propagation algorithm （BPNN） which has a better structure and been widely used. But there are still many drawbacks if we simply use feed-forward neural network, such as slow training rate, easy to trap into local minimum point, and bad ability on global search. In this paper, feed-forward neural network trained by PSO （particle swarm optimization） algorithm is proposed for fault location scheme in 500 kV transmission system with distributed parameters presentation, The purpose is to simulate distance protection relay. The algorithm acts as classifier which requires phasor measurements data from one end of the transmission line and DFT （discrete Fourier transform）. Extensive simulation studies carried out using MATLAB show that the proposed scheme has the ability to give a good estimation of fault location under various fault conditions.

A Transmission Line Fault Classification Approach by Support Vector Machines

This paper presents an approach for shunt faults detection and classification in transmission line using Support Vector Machine （SVM）. The paper compares between using three line post-fault current samples for one-half cycle and one-fourth cycle from the inception of the fault as inputs for SVM. Two SVMs are used, first SVMabc is used for faulty phase detection and second SVMg is used for ground detection. SVMs with polynomial kernel with different degrees are used to obtain the best classification score. The classification test results show that the proposed method is accurate and reliable.

Single-end Protection Scheme Based on Transient Power Waveshape for Hybrid HVDC Transmission Lines

The recent in-depth development of hybrid highvoltage direct current(HVDC) transmission systems poses looming adaptability challenges to protection. The various and disparate direct current(DC) transmission topologies can profoundly affect the operating characteristics of DC transmission networks, which result in the lack of performance of conventional DC protection schemes in such topologies. This significantly limits the application of hybrid HVDC technologies. This paper proposes a single-end protection scheme based on the transient power waveshape for fast and sensitive detection and classification of different types of DC faults in hybrid HVDC transmission lines. The fault characteristics and their causes under different fault conditions are analyzed in detail with a pre-introduced linearized transient model of a hybrid HVDC transmission system, demonstrating that the formation of the fluctuation characteristics of local measurements is mainly determined by the buffering and absorption effects of lumped-parameter reactors on transient traveling-wave(TW) energy. Simulation results verify the sensitivity, rapidity, reliability, and anti-interference ability of the proposed scheme when applied to hybrid HVDC transmission lines. Furthermore, it is confirmed that the proposed scheme is adaptable to symmetric voltage-sourced converter(VSC) and conventional line-commutated converter(LCC) based HVDC transmission lines.

Applying Modern Communication Technology to Loss-of-Mains Protection

The protection of distribution networks is facing new challenges from an increasing amount of DG （distributed generation）. Even though current technology provides satisfactory solutions to manage this new situation, LOM （loss-of-mains protection） is still considered problematic. The solution proposed in this paper focuses on the use of a line differential protection relay. It inherently contains a suitable communication channel and provides absolutely selective protection for the feeder. Furthermore, it prevents the feeder relays from false tripping for faults on the neighboring feeder. The present trend in protection communication points towards the use of fiber optics. For line differential protection, this means a fast and high-capacity communication link which enables the implementation of many advanced protection functions. In addition, a solid foundation for such a communication link is offered by the new IEC 61850 standard and Ethernet technologies. The basic functionality of the line differential protection enables the operation of both the feeder protection and the DG protection for any fault on the feeder. Furthermore, basic LOM protection methods can be applied as backup protection for failures on the communication link.

Measured Impedance and Threshold Value of Electrode Line Impedance Supervision Based Protection in HVDC Transmission System

At present,electrode line impedance supervision(ELIS)based protection is widely used to detect faults on grounding electrode lines,which are indispensable elements of high-voltage direct current(HVDC)systems.The existing theoretical analysis of measured impedance is based on lumped line model and the threshold value is generally set according to engineering experience,which have caused the dead zone problem and even accidents.Therefore,a study on measured impedance of ELIS-based protection and its threshold value selection method is carried out to solve this problem.In this study,the expressions of measured impedance under normal operation and fault conditions are deduced based on rigorous and accurate line model.Based on the expressions,the characteristics of the measured impedance are calculated and analyzed.With the characteristics of the measured impedance,the applicability of the protection with the traditional threshold value is further discussed and the distribution of the dead zone can be located.Then,the method to calculate the threshold value of ELIS-based protection is proposed.With a proper threshold value selected by the proposed method,the dead zone of ELIS-based protection is effectively eliminated,and the protection can identify all types of faults even with large transition resistances.Case studies on PSCAD/EMTDC have been conducted to verify the conclusion.

Research on Common Grounding Electrode Technique in HVDC

This paper discusses the characteristics of DC transmission common system ground electrode type and shared ground electrode, established the mathematical model of two circuit DC systems share ground electrode, analyze effects of the shared loop ground DC transmission system electrode on the operation of HVDC system size under different operation modes, and compare with the independent ground electrode, ground electrode impact on environment under different operation mode, and the paper finally puts forward some solving measures for the influence of the shared ground electrode on the environment and public ground electrode effects on DC system operation problems.

Study on Connection of Spatial Planning of Oil and Gas Infrastructure and Environmental Sensitive Area

By analyzing the influence of pollution factors in each process on the environmentally sensitive area in construction and operation of oil and gas infrastructure,main problems were obtained:delimitation and implementation of three control lines in land space planning,relevant environmental protection laws and regulations not perfect and specific,delimitation of environmentally sensitive area lack of sufficient demonstration,"conditional permission to pass"not be raised to an explicit provision,urban energy corridor planning not fully implement the concept of environmental protection,and the idea of adjacent spatial planning not be implemented yet.Moreover,it put forward countermeasures and suggestions for the construction department of oil and gas infrastructure.

Node line semimetal states in tungsten-based materials

Node line semimetals(NLSMs) were characterized by one-dimensional band crossings in their bulk electronic structures.The nontrivial band topology of NLSM gives rise to "drumhead" surface electronic excitations that exhibits exotic physical properties.The symmetries of crystalline provide the needed protection of node line from being gapped out by the perturbations that preserve the symmetry.The progress of NLSM in tungsten-based materials is reviewed with an emphasis on their symmetry-based protection,characteristic electronic band structures and their response to the spin-orbit coupling(SOC)and breaking of time-reversal symmetry.The potential exploration directions of tungsten-based NLSM in the future are also discussed.

Application of new directional logic to improve DC side fault discrimination for high resistance faults in HVDC grids

This paper proposes a simple and fast way to determine the direction of a fault in a multi-terminal high voltage direct current(HVDC) grid by comparing the rate of change of voltage(ROCOV) values at either side of the di/dt limiting inductors at the line terminals. A local measurement based secure and fast protection method is implemented by supervising a basic ROCOV relay with a directional element. This directional information is also used to develop a slower communication based DC line protection scheme for detecting high resistance faults. The proposed protection scheme is applied to a multi-level modular converter based three-terminal HVDC grid and its security and sensitivity are evaluated through electromagnetic transient simulations. A methodology to set the protection thresholds considering the constraints imposed by the breaker technology and communication delays is also presented. With properly designed di/dt limiting inductors,the ability of clearing any DC transmission system fault before fault currents exceeds a given breaker capacity is demonstrated.

A positive-sequence current based directional relaying approach for CCVT subsidence transient condition

In this work,a directional relaying algorithm is proposed for transmission line to prevent relay maloperation during coupling capacitor voltage transformer(CCVT)subsidence transient.The effect of CCVT subsidence transient during single-pole-tripping condition is highlighted in this paper.The proposed method which is based on phase angle difference of post fault and prefault positive sequence current can help the directional relay to take accurate decision during erroneous CCVT secondary response.The available CCVT model in PSCAD is not able to generate significant subsidence transient in the secondary side.So,a new CCVT model is developed in EMTDC/PSCAD domain for transient response analysis and to check the relay operation.Next,the performance of different voltage and current information based directional relaying techniques have been analyzed and compared with the proposed method.The results are evaluated for different system and fault conditions.Results demonstrate the accuracy of the proposed method.