Safe Operation Of Power System Research Articles

Novel Method for Rapidly Constructing Active Power Steady-State Security Regions Incorporating the Equivalent Reactances of TCSCs

Active power steady-state security regions (APSSRs), which can provide guidance for prevention and control through security checks, is of great importance for the safe operation of power systems in which more and more sustainable energy power generation is integrated. As a mature flexible AC transmission system (FACTS) device, thyristor-controlled series compensators (TCSCs) can carry out series compensation for the transmission line by controlling its equivalent reactance. With the change of the equivalent reactance parameter of a TCSC, the nodal admittance matrix and power flow distribution of the power system also changes. Inevitably, the APSSR will be different. Therefore, it is necessary and important to further incorporate the equivalent reactance parameters of TCSCs in the APSSR expression, which is generally established in the space of node active power injections. In this paper, a rapid construction method of APSSRs incorporating the equivalent reactances of TCSCs is proposed. Firstly, applicability and efficiency of the conventional APSSR construction method for power systems with TCSCs are analyzed. Further, with equivalent disconnection of TCSC branches, the effect of TCSC equivalent reactances on the distribution of active power flow through changing the structure parameters is treated as modifying node active power injections. On this basis, explicit expressions of APSSRs with a single TCSC equivalent reactance parameter and double TCSC equivalent reactance parameters are derived, respectively. Moreover, by deducing the general formula of APSSRs with multiple TCSC equivalent reactance parameters, the feasibility of the proposed method for power systems with multiple TCSCs is analyzed. Eventually, via benchmarks with different scales and a different number of TCSCs, validity and superiorities of the proposed method in computational efficiency are demonstrated.

Corrosion Rate Simulation and Influence Factors of a Vertical DC Grounding Electrode

Corrosion affects the performance of grounding electrode materials buried in soil and threatens the safe operation of power systems. Natural corrosion of grounding electrode materials occurs over a long time and involves many influencing factors. Simulating the true corrosion environment of grounding electrode materials, exploring the corrosion mechanism, and accurately determining the corrosion condition of these materials are problems that must be solved urgently. In this paper, a corrosion simulation model of a vertical carbon steel grounding electrode was built based on the principle of electrochemical corrosion. The influence of soil parameters (oxygen concentration, pH value, and chloride ion concentration) on the corrosion characteristics of the grounding electrode was calculated. The corrosion rates of the vertical grounding electrode at different burial depths were compared with and without direct current. Simulation results showed that the corrosion rate of the grounding electrode changed linearly with oxygen concentration in the soil, changed negatively and exponentially with pH, and changed logarithmically with chloride ion concentration. Grounding electrode materials should be buried at a depth of 2 m when the time with no current in the grounding electrode is more than that with current. This burial depth can effectively reduce the influence of oxygen concentration on grounding corrosion. Moreover, the local reduction in hydrogen ion content must be considered during the construction of a grounding electrode to ensure that the grounding electrode surface is in a strong alkaline environment, which can passivate the grounding electrode and reduce the corrosion rate.

Ultra-Short-Term Multistep Wind Power Prediction Based on Improved EMD and Reconstruction Method Using Run-Length Analysis

With larger scale wind farm being connected to the power grid, the high-precision wind power prediction has become an important means which can ensure the safe operation of power system. The large fluctuations or abnormal data which exist in the local wind power sequences may lead to the phenomenon of over-iterative decomposition of the classical empirical mode decomposition (EMD). In response to this defect, first, the raw wind power sequences are decomposed using improved EMD with introducing the weight function and modifying the mean judgment condition in the classical EMD. Then, the reconstruction strategy based on run-test analysis is proposed based on the fluctuation characteristics of the decomposed components. Finally, the ultra-short-term prediction of the high-frequency item, the middle-frequency item, the low-frequency item, and the trend item in the reconstruction sequences are performed according to different prediction methods. The wind power data of three wind farms in northeast China were selected for forecasting analysis. The analysis shows that compared with other classical prediction methods, this method can effectively improve the prediction accuracy and verify the effectiveness of the proposed method.

The need of creating a new nominal creepage distance in accordance with heaviest pollution 500 kV overhead line insulators

Abstract The flashovers on insulators, caused by severe pollution, has posed the biggest threat on the safe operation of power systems the insulators contamination, and it is an important problem, special in polluted. The aperiodic occurrence of widespread contamination related outages cause serious damages to the transmission lines, the worst behavior is up to 500 kV overhead lines. The exceptional level of pollution measured on those insulators, especially for the bottom surface for the non-soluble salt deposit density (NSDD) component, where the values are outside of the standard limit given in the currently IEC standard. The results provide important reference for the insulators design, maintenance of operational transmission line insulators and flashover warnings. It should be highlighted that results fall out of the limit of the IEC standard and that in order to plot those values in the graph the limits for the highest NSDD values have been increased from 4 to 20 g/cm2. This clearly shows the unusually high values of the NSDD components measured on those insulators. The case study has been realized on 837,000 insulators for 9000 towers in 500 kV powers lines. This clearly shows the unusual characteristics of the coast and desert environment of the 500 kV overhead lines, and the needs of update in the IEC standards has been researched.

Extended Gersgorin Theorem-Based Parameter Feasible Domain to Prevent Harmonic Resonance in Power Grid

Harmonic resonance may cause abnormal operation and even damage of power facilities, further threatening normal and safe operation of power systems. For renewable energy generations, controlled loads and parallel reactive power compensating equipment, their operating statuses can vary frequently. Therefore, the parameters of equivalent fundamental and harmonic admittance/impedance of these components exist in uncertainty, which will change the elements and eigenvalues of harmonic network admittance matrix. Consequently, harmonic resonance in power grid is becoming increasingly more complex. Hence, intense research about prevention and suppression of harmonic resonance, particularly the parameter feasible domain (PFD) which can keep away from harmonic resonance, are needed. For rapid online evaluation of PFD, a novel method without time-consuming pointwise precise eigenvalue computations is proposed. By analyzing the singularity of harmonic network admittance matrix, the explicit sufficient condition that the matrix elements should meet to prevent harmonic resonance is derived by the extended Gersgorin theorem. Further, via the non-uniqueness of similar transformation matrix (STM), a strategy to determine the appropriate STM is proposed to minimize the conservation of the obtained PFD. Eventually, the availability and advantages in computation efficiency and conservation of the method, are demonstrated through four different scale benchmarks.

Harmonic Estimation Base on Center Frequency Shift Algorithm

Harmonic pollution has been a key issue affecting the safe operation of power system. But the traditional harmonic analysis methods are easy to be affected by the environmental factors. In order to reduce the impact of these disturbances, a novel harmonic analysis method based on center frequency shift is presented. The harmonic spectral lines located at the half frequency points is need for frequency shift in time domain. However, to considering the harmonic spectral lines after frequency shift will not be just in the ideal position, an offset factor is proposed for modifying the position of the harmonic spectral lines. At the same time, the corresponding formulas to estimate the magnitude, phase angle and frequency are deduced. The simulation results show that the FFT harmonic parameter estimation algorithm based on center frequency shift is effective. The parameters of harmonic signals can be accurately estimated by the algorithm. And the interference factors can also be suppressed.

Fuzzy Comprehensive Evaluation Algorithm for Power Information System Security Level Based on the Internet of Things

With the development of information and communications technology, communication technology has been widely used in the electric power industry and has brought threats to the safe operation of power systems. Things can not only connect people; things can also connect other things. Therefore, the Internet of things plays an important role in power information system security. This study proposes a triangular fuzzy number weight method to calculate the index weight based on the analysis of the existing fuzzy algorithm and the security of a power information system. A fuzzy comprehensive evaluation model is established in accordance with matrix theory, statistical theory, and other methods after experimental data are analyzed. Results show that this algorithm can accurately evaluate system status and provide reference for managing power systems. The fuzzy algorithm for power information system security level ensures the safe operation of the power system and promotes its healthy development. This algorithm can significantly promote economic development in China.

Application Research of the Sparse Representation of Eigenvector on the PD Positioning in the Transformer Oil

The partial discharge (PD) detection of electrical equipment is important for the safe operation of power system. The ultrasonic signal generated by the PD in the oil is a broadband signal. However, most methods of the array signal processing are used for the narrowband signal at present, and the effect of some methods for processing wideband signals is not satisfactory. Therefore, it is necessary to find new broadband signal processing methods to improve detection ability of the PD source. In this paper, the direction of arrival (DOA) estimation method based on sparse representation of eigenvector is proposed, and this method can further reduce the noise interference. Moreover, the simulation results show that this direction finding method is feasible for broadband signal and thus improve the following positioning accuracy of the three-array localization method. And experimental results verify that the direction finding method based on sparse representation of eigenvector is feasible for the ultrasonic array, which can achieve accurate estimation of direction of arrival and improve the following positioning accuracy. This can provide important guidance information for the equipment maintenance in the practical application.

Research on Intelligent Online Monitoring and Evaluation of Power Transformer

Transformer is the power equipment of power system core. Intelligent monitoring and operation of transformer can not only monitor the full range of the transformer, the realization of state evaluation, it should be required repair, maintenance required good, but also on the latent fault early diagnosis and prediction. Research on transformer intelligent monitoring and operating technology of safe operation of power system and the substation has great significant and impoertance. According to the theory and method of transformer intelligent, combined with intelligent transformer on-line monitoring technology has been achieved, mainly explores the intelligent cooling and adjustable transformer pressure control technology.

Investigating the Effect of Demand Side Management on the Power System Reliability

In electric power systems, the generated power should be equal with the demand and power of network is mainly controlled through generation system. In such operation, the demand is satisfied through changing the generated power and afterward, the safe operation of power system is reached. But during recent years, a new concept has been developed in electric power systems namely demand side management (DSM). DSM is the modification of consumer demand for energy through various methods such as financial incentives and education. Usually, the goal of demand side management is to encourage the consumer to use less energy during peak hours, or to move the time of energy use to off-peak times such as nighttime and weekends. One of the important models of DSM is interruptible loads. Interruptible loads are the right for an electricity utility to interrupt supply to a customer, typically during a system emergency, to relieve short term network constraints up to a couple of hours. Interruptible loads can be deployed in one of two ways. The network operator gives notice of an interruptible load event to the customer, then relies on the customer to reduce their electricity usage; or unilaterally interrupts supply to the customer. In this paper, the effect of interruptible loads on the power system reliability is investigated. A multi machine power system is considered as cases study. Simulation results show the great effects of interruptible loads on the power system reliability.

Evaluation for Voltage Stability Indices in Power System Using Artificial Neural Network

At present, the evaluation of voltage stability assessment experiences sizeable anxiety in the safe operation of power systems. This is due to the complications of a strain power system. With the snowballing of power demand by the consumers and also the restricted amount of power sources, therefore, the system has to perform at its maximum proficiency. Consequently, the noteworthy to discover the maximum ability boundary prior to voltage collapse should be undertaken. A preliminary warning can be perceived to evade the interruption of power system's capacity. This paper considered the implementation of real-time system monitoring methods that able to provide a timely warning in the power system before the voltage collapse occurred. Numerous types of line voltage stability indices (LVSI) are differentiated in this paper to resolve their effectuality to determine the weakest lines for the power system. The line voltage stability indices are assessed using the IEEE 9-Bus and IEEE 14-Bus Systems to validate their practicability. Besides that, this paper also introduced the implementation of real-time voltage stability monitoring by using Artificial Neural Network (ANN). Results demonstrated that the calculated indices and the estimated indices by using ANN are practically relevant in predicting the manifestation of voltage collapse in the system. Therefore, essential actions can be taken by the operators in order to dodge voltage collapse incident from arising.

Transformer Bushing Online Monitoring Method Based on the Method of Relative Angle Difference

Transformer is the main equipment of power system, its operation reliability is directly related to power system security and reliability of power supply. In order to guarantee the safe operation of power system, must strengthen the monitoring of the main transformer.With the development and popularization of intelligent station, the detection of transformers insulation is faced with the new problem that PT signal is not convenient to get and even unable to get. This paper proposes the relative method which is used to calculate and monitor dielectric loss of transformer bushing and designs the on-line monitoring device, through the data acquiring form the on-line monitoring instrument which are installed in the transformer of substation shows that this method has high precision, strong anti-interference ability.

Detection of UV Pulse from Insulators and Application in Estimating the Conditions of Insulators

Abstract Solar radiation in the band of 240–280 nm is absorbed by the ozone layer in the atmosphere, and corona discharges from high-voltage apparatus emit in air mainly in the 230–405 nm range of ultraviolet (UV), so the band of 240–280 nm is called UV Solar Blind Band. When the insulators in a string deteriorate or are contaminated, the voltage distribution along the string will change, which causes the electric fields in the vicinity of insulators change and corona discharge intensifies. An UV pulse detection method to check the conditions of insulators is presented based on detecting the UV pulse among the corona discharge, then it can be confirmed that whether there exist faulty insulators and whether the surface contamination of insulators is severe for the safe operation of power systems. An UV-I Insulator Detector has been developed, and both laboratory tests and field tests have been carried out which demonstrates the practical viability of UV-I Insulator Detector for online monitoring.

Study on Online Monitoring System of Power Transformer

This paper puts forward an on-line monitoring system of power transformer which could online collect multiple physical parameters of power transformer at the same time without using electricity sensor. In this case, the sensor will not affected by the strong electric field, magnetic field and electromagnetic wave. The system analysis the running state of power transformer according to physical parameters accurately, as current technology can only measure single physical parameters, it can solve this problem that the measurement results lack of association. Moreover, the system improves the reliability of power transformer operation and security of online measurement, ensuring the safe operation of power system.

Predictive Model for Equivalent Ice Thickness Load on Overhead Transmission Lines Based on Measured Insulator String Deviations

Transmission-line icing presents a serious threat to the safe operation of power systems. Therefore, the icing condition of overhead transmission lines must be accurately calculated for online monitoring and prewarning systems. Based on the icing data obtained at Xuefeng Mountain Natural Icing Stations (XMNIS), the cross-sectional shape of glaze icing on conductors was studied, and the correction coefficient of the actual nonuniform ice was proposed to provide an accurate and convenient method for field icing measurement. In addition, by analyzing the characteristics of the tension and tilt of the insulator string at the iced tangent tower, a new mechanical calculation model considering the ice and wind loads was established. One-month field observations and experiments were conducted in XMNIS, and it is shown that the calculation results have good agreement with experiment results, which suggests that the model can be used for ice thickness calculation and online monitoring on transmission lines.

Application of Database Technology in Fault Extract for Shipboard Power System

The shipboard power system network dispatch automation was a recently developed technology which can effectively enhance supply and distribution electrical power system safe operation ability and reliability. With science and technology development, the shipboard power system is getting more and more complex, it is very important to extract the fault accurately and quickly. Based on the characteristics of the shipboard power system, the database technology was used to solve the fault extraction for the shipboard power system network. Simulation results showed it can satisfy real time request and process multi-fault situation appeared in the system and show all the fault branches information.

Development of Combined Monitoring System of MOA Insulating Material and CT (Casing Tube) Insulating Material

Live testing of resistive current of metal oxide arrester (MOA) and on-line monitoring of capacitive current of capacitor voltage transformer or casing tube (CT) are two important parameters for stable and safe operation of power system. The present method is to separately monitor these two types of equipment. Through analyzing equipment structure, monitoring principle, integration mechanism and so on, this article realizes combined measurement of resistive current and capacitive current. Thus, the combined monitoring of metal oxide arrester (MOA), rheology and CT insulation status is achieved.

Summary of the Stability Chanllenges and Safe Operation of Power Systems in View of Dispatching

The Internet and the gradual implementation of the continuous power grid market in recent years make the power system more complex under different operating environment. Safe and stable operation of power grids have become increasingly important . With the rapidf development of the grid and constant innovation, safe and stable operation also has a new requirement , because the rapid development of the power system brings more This paper analyzes the causes of blackouts and reviews security of the power system stability problems related to measures on the security and stability of the power system operation .

A Double Exponential Function Fitting Algorithm for Optimize Parameter of μH Curve

Saturable magnetic circuit is a common phenomenon in power system. It can lead to waveform distortion, coefficient of self-inductance decrease and measurement error increase. So establishing a mathematical model for saturable magnetic circuit and revealing the mathematical relationships in saturable phenomenon. It is helpful to reliable and safe operation of power system. This paper base on double expontential function fitting algorithm and simplex algorithm to establish the function relationship between relative permeability and magnetic field intensity. Applying for the model,we can obtain the waveform of magnetic flux in transformer core and transformer voltage waveform. The research has certain significance in the abstract and foreground in the application for the study of saturable phenomenon.

The Influence of External Climate Environment on Safe Operation of Power System

Frequency and severity of some extreme weather events are increasing, and weather can impact the power system and its components in a number of ways. This paper identifies key technical issues facing the electric power industry, related to global climate change. The technical challenges arise from: 1) impacts on supply and demand balance; 2) impacts on system operating strategies, and power generation scheduling; 3) impacts on power grid structure, and power infrastructure response to extreme weather events; and 4) impacts on operation parameters of power system. The objective of this paper is to facilitate continued discussion of power systemclimate change interactions. To this end, this paper identifies key issues relating to the interactions between the electric power industry and global climate change. These issues will not be resolved quickly, and it requires sustained attention if they are to be resolved successfully.