Characteristic Analysis of UHVAC/DC Hybrid Power Grids and Construction of Power System Protection

Strong DC coupling with weak AC and large-scale renewable energy integration are the two significant characteristics of ultra-high-voltage AC/DC(UHVAC/DC)hybrid power grids in China.Strong coupling between AC and DC grids and the different integration performance of renewable energy sources have profoundly changed the stability characteristics of the power system.The traditional stability control system is inadequate for the stability control of UHVAC/DC power grids.This paper analyzes the requirements for constructing an integrated defense system in a UHVAC/DC hybrid power grid(i.e.power system protection).The definition,connotation,and designing principles of power system protection are put forward.The relationship between the power system protection and the traditional three-defense lines is investigated.The design principles,general hardware structure and main functions of a power system protection are presented.Key problems and technologies are specified in the construction of the power system protection.

Improving the performance of power system protection using wide area monitoring systems

Wide area monitoring(WAM) offers many opportunities to improve the performance of power system protection. This paper presents some of these opportunities and the motivation for their development. This methods include monitoring the suitability of relay characteristics,supervisory control of backup protection, more adaptive and intelligent system protection and the creation of novel system integrity protection scheme. The speed of response required for primary protection means that the role WAM in enhancing protection is limited to backup and system protection. The opportunities offered by WAM for enhancing protection are attractive because of the emerging challenges faced by the modern power system protection. The increasingly variable operating conditions of power systems are making it ever more difficult to select relay characteristics that will be a suitable compromise for all loading conditions and contingencies. The maloperation of relays has contributed to the inception and evolution of 70 % of blackouts,thus the supervision of the backup protection may prove a valuable tool for preventing or limiting the scale of blackouts. The increasing interconnection and complexity of modern power systems has made them more vulnerable to wide area disturbances and this has contributed to several recent blackouts. The proper management of these wide area disturbances is beyond the scope of most of the existing protection and new, adaptive system integrity protection schemes are needed to protect power system security.

Developments of power system protection and control

Synchronized wide area communication has become a mature technology,which makes the real-time interaction between the substations and the wide area protection and control system possible.However,the present protection and control system to handle this real-time data has been recognized to be deficient.This paper begins by reviewing the development history of power system protection,with special attention paid to the recent development in the field of wide-area and integrated protections,in order to look into the future development of protection and control systems.Then the concept of integrated wide area protection and control is introduced,where it can be shown that a hierarchical protection and control system provides the protection and control for wide area or regional power substations/plants and their associated power networks.The system is mainly divided into three levels:the local,the substation/plant,and the wide area/regional.The integrated functions at each level are described in details with an aim to develop an optimal coordination mechanism between each level.The key element in the proposed system is the wide area real-time protection and control information platform,which not only enables the merger of three lines of defence for power system protection and control,but also provides a perfect tool for the application of cloud computing in substations and power networks.

Serial Failure Diagnosis of a Transmission Line Protection Relaying System by Petri Nets

With the development of large-scale complicated modern power systems, the requirement for the associated protection scheme tends to be more stringent and its combination more complex. However, it is very difficult to figure out the factors of failure of such systems. This paper proposes a Petri net model of a transmission line protection relaying system, including three types of relays as well as an automatic reclosing device, and shows how to diagnose serial failure of the system by analyzing invariant sets of the model. Furthermore, it gives four basic types of failure sequences and its execution is much more intuitive and effective than the traditional method.

Adaptability of the Recloser-Fuse Protection Scheme in the Presence of Distributed Generation

This paper addresses the behaviour of an IEEE(Institute of Electrical and Electronics Engineers)test network when distributed injections are added to the distribution network.The penetration of different dispersed generation technologies,modifies the distribution system characteristics,with impact on a number of parameters,depending on their size and location on the network.For this purpose,this paper comprises three case studies:in the first case an exhaustive analysis is carried out of the occurrence of faults throughout the network,along with the introduction of distributed generators;in the second case the network behavior is assessed against the use of three of the most commonly used types of generators based on rotating machines;in the third case study an evaluation is made of the network performance when the three types of DG(distributed generation)units are distributed in multiple buses.In all cases the protection system is analyzed with the aim of ensuring coordination among the protection devices.All simulations are performed using the Power Factory software package from DigSILENT.From the simulation results,conclusions are drawn that provide insights into the behaviour of protection systems,highlighting the limitations of the original protections and coordination with different distributed generators technologies.

Human reliability analysis in maintenance team of power transmission system protection

The requirement for reliable electrical energy supply increases continuously because of its vital role in our lives.However,events due to various factors in the power grid can cause energy supply to be interrupted.One of these factors is human error and thus human reliability analysis is a serious element in the industry.The first step is to identify the roots of human error,on which there has been limited research in this area.In this paper,the potential and actual causes of human error in maintenance teams of power transmission system protection are identified and predicted within a framework of human factors analysis and classification system method.Then,human error factors are ranked to help improve human reliability.The proposed method is implemented in the Fars Electricity Maintenance Company.

Fault Location Method for STATCOM Connected Transmission Lines Using CCM

Determining the fault location using conventional impedance based distance relay in the presence of FACTS controllers is a challenging task in a transmission line. A new distance protection method is developed to locate the fault in a transmission line compensated with STATCOM with simple calculations. The proposed protection method considers the STATCOM injected/absorbed current to correct the fault loop apparent impedance and accordingly calculates the actual distance to the fault location. The comprehensive equations needed for apparent impedance calculation are also outlined and the performance is evaluated and tested with a typical 400 KV transmission system for different fault types and locations using MATLAB/SIMULINK software. The evaluation results indicate that the new protection method effectively estimates the exact fault location by mitigating the impact of STATCOM on distance relay performance with error less than 0.3%.

A Niche-Based Evolutionary Tabu Search Algorithm for Optimal Coordination of Protection Relays in Power Networks

In this paper, refusal of operation and the degree of constraint violation are considered as one part of the objective function for optimizing the protection relay setting coordination of over current relays in power systems; a new expression of objective function in this optimization problem is proposed. To combine the advantages of both Tabu search （TS） and evolutionary algorithms （EAs）, a new niche-based evolutionary Tabu search algorithm （named NETS） is presented to solve this optimization problem. Moreover, in two cases of power networks, comparisons between NETS and two published algorithms are given. Experimental results show the expression of the objective function for protection relay setting is feasible and reasonable, and the proposed algorithm NETS exhibits a good performance.

Micro-synchrophasor based special protection scheme for distribution system automation in a smart city

Introduction:Aspects of power system protection which contributes to mal-operations and blackouts can be improved by supervision of system behavior and response based analysis rather than condition-based or event-based analysis using wide area measurements based on synchrophasor technology.The paper explores the application of micro-Phasor Measurement Unit for time synchronized real-time distribution network monitoring and agile decision support schemes for system prognosis and control.Case description:The scheme is proposed as part of a project on“Power System Voltage Stability Analysis using synchrophasors in Distribution System of Kerala Grid”at Kerala State Electricity Board Ltd.An actual grid occurrence during the severe tropical cyclone Ockhi,is considered as the base case which motivated the work.Discussion and evaluation:A voltage stability index(VSI)based special protection scheme(SPS)for radial distribution network at a proposed smart city is presented in the present study.The proposed special protection scheme on actual implementation can use data from proposed local micro-Phasor Measurement Unit.The PMU is proposed to be placed at one of the key nodes of the distribution system network in the city.Conclusion:The VSI is derived using local phasor values and is used to initiate a Special Protection Scheme for N-1 contingency at the key node,so as to ensure availability of the most essential feeder which provides supply to a hospital campus housing several health institutes of prime importance.The voltage stability index derived is tested and SPS is validated using real-time grid data.

Fast Identification of Symmetrical or Asymmetrical Faults During Power Swings with Dual Use Line Relays

Increasing power demand,penetration of renew-ables,and limitations of necessary grid expansion are proffering new challenges to existing power system protection and control strategies.However,with the advancement in intelligent elec-tronic devices and relaying technology,fast,accurate and reliable protection schemes can be developed for smart power systems.In this paper,a new protection scheme based on admittance and power change has been proposed with dual-use line relays to detect symmetrical/asymmetrical faults in power systems.A large number of fault environments have been simulated by varying fault distances from relay location,fault resistance,and power angle in single machine infinite bus and WSCC 9-bus systems.Some crucial decisive fault scenarios e.g.close in/far end faults,faults in series compensated line,faults during asymmetrical swings,switching ON/OFF large loads,single and multi-modal swings have also been verified for the proposed index.In this paper,for the first time,detection of faults during power swings have been examined and verified in the presence of wind farms.The simulation results show the proficiency of the proposed algorithm for detecting faults in the presence or absence of power swings.

Summary of Useful Concepts About the Coordination of Directional Overcurrent Protections

This paper summarizes some useful concepts about the coordination of directional overcurrent protections.The following key topics are described:the analysis of systems in a ring configuration and only one source of short-circuit currents;the impossibility of obtaining selectivity for all the possible system configurations with multiple sources;the need for inverse functions in order to obtain selectivity in systems with multiple sources;the coordination with protections for radial loads;the coordination between instantaneous and delayed functions;the considerations to select the pickup values;the influence of contributions from motors to short circuit currents;the transient configurations due to sequential trips at both line ends;the influence of dynamic behavior of overcurrent functions;the influence of stability constraints;other specific considerations for ground functions;some specific considerations for systems with distributed generation.A summary of these points and their effect on the coordination of directional overcurrent protections is not available in the current literature.This novel description should facilitate the inclusion of these key points in research and coordination studies related to these protective functions.

Comprehensive power swing detection by current signal modeling and prediction using the GMDH method

Power swing is an undesirable variation in power flow. This can be caused by large disturbances in demand load, switching, disconnection or reclosing lines. This phenomenon may enter the zones of distance relays and cause relay malfunction leading to the disconnection of healthy lines and undermining network reliability. Accordingly, this paper presents a new power swing detection method based on the prediction of current signal with a GMDH (Group Method of Data Handling) artificial neural network. The main advantage of the proposed method over its counterparts is the immunity to noise effect in signals. In addition, the proposed method can detect stable, unstable, and multi-mode power swings and is capable of distinguishing them from the variety of permanent faults occurring simultaneously. The method is tested for different types of power swings and simultaneous faults using DIgSILENT and MATLAB, and compared with some latest power swing detection methods. The results demonstrate the superiority of the proposed method in terms of response time, the ability to detect power swings of different varieties, and the ability to detect different faults that may occur simultaneously with power swings.

Phasor-domain Dynamic Model of Asymmetric Current Injection Controller for Converter-interfaced Generator

This paper presents a controller model of asymmetric current injection for converter-interfaced generators suitable for root-mean-square(RMS)phasor-domain,fundamentalfrequency,three-phase,and dynamic simulation tools.The effectiveness of the proposed controller is assessed with simulations in test systems with high percentage of converter-interfaced generation.The simulations focus on the operation of protection relays that use negative-sequence quantities in their directional elements.This paper also presents and compares two strategies to limit reactive negative-sequence currents,and active and reactive positive-sequence currents.A tutorial test system and a regional system part of the actual Brazilian Interconnected Power System are used to assess the correctness of the proposed controller in three-phase fundamental-frequency RMS dynamic simulations.

A review of superconducting fault current limiters compared with other proven technologies

Several substations in operation were commissioned decades ago.These substations are overstressed,then their protection equipment cannot provide an effective safety condition to the system.In the worst cases,short‐circuits can cause permanent damage to the system if the overcurrent is higher than the capacity of the installed equipment.There are some possible solutions for those cases:replace all the equipment in the overstressed substation,build a new one in parallel or install a fault current limiter(FCL)device.From an economic point of view,introducing FCLs in the power system is the best way to solve the described problem.The commercial solutions available are the pyrotechnic FCL,air coil reactor,neutral earthing resistor,and high impedance transformer.However,these devices are limited and present several drawbacks.Since the’70s,there has been a search for reliable FCL devices that do not interfere in the regular operation of substations and could limit the fault currents to the protection system rated level.There were so many FCL technologies proposed in the last decades.These proposed new devices may use superconducting technologies,power electronics,or both.This paper reviews proven FCL technologies,focusing on full‐scale devices demonstrated in field and lab tests.The goal is to introduce the main FCL technologies in development and discuss didactically their operation principle,the built prototypes,the commercial units,whether they exist,and the main drawbacks for each technology presented.A final analysis of the level of maturity for each FCL technology is discussed using the TRL(Technology readiness level)scale in order to find technologies with more potential for mass production.The three technologies closer to the full commercial application are:the Resistive Superconducting FCL,the Saturated Iron Core FCL,and the Series Reactor FCL.