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.

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.

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.

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.

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.