The accuracy of the load model has great effects on power system stability analysis and control. In order to solve the problem of the difficulty of establishing accurate load model and the complexity of the modeling the non-linear properties of dynamic load , this paper proposes a methodology based on the RRBFNN (recurrent RBF neural network) on modeling load from field measurements. New method is proposed to model power system load, which consists of recurrent network (RNN) and radial basic function (RBF) network and uses the ability of RNN for learning time series and the property of RBF with self-structuring and fast convergence. This new method which is tested by computer simulations on benchmark New Fngland test system and applied in model identification of composite load for power system, has been proved its validity and accuracy.
This paper presents a novel strategy based on pattern discovery algorithm and extended A-Nearest Neighbor (k- NN) classifier to design the power system transient stability assessment (TSA) scheme. A pattern discovery algorithm based on residual analysis and recursive partitioning is employed to identify the latent structure (called pattern) of data samples. An extended A-NN classifier is then designed to label the input sample with stability levels where the identified patterns are applied as initial classified data set. In order to improve the pattern discovery efficiency, a feature selection process is introduced in the first stage to extract kernel-feature subset from the pre-contingency steady state parameters as the input features for the TSA scheme. Applications of the proposed scheme on two IEEE test systems prove its feasibility and show good performance in stability level classifications.
With rising electricity loading in developing country, measuring capacity of pumped-storage station (P-S station) is becoming more critical. This paper tries to establish mathematic model on obtaining capacity of P-S station for maximum cost savings. The paper first deducts the relationship between capacity of P-S station, peak load and the vale load by simulating cost curve of thermoelectric unit, and then deducts the formula for calculating optimal capacity of P-S station. Based upon these findings and the load curve, the paper then develops the curve to describe the relationship between volume of generated electricity and capacity of the P-S station and provides the solution for obtaining optimal capacity of the P-S station. Finally, the paper discusses the impact of selecting initial solution or certain iterative solution on iterative speed and suggests the direction for further research.
This paper introduces an interval-based approach in economic evaluation on power construction projects. Firstly, interval models are set up to extend classic methods, including Interval Net Present Value method, Interval Payback Period method, Interval Internal Rate of Return method. Additionally, a method to measure risk is also proposed. Then, cases are given to test and compare these interval methods under both certain and uncertain life period conditions. Case study suggests that the interval-based methods are efficient and flexible to deal with evaluation problems on power construction projects, which can effectively judge the feasibility of a project, as well as estimate the risk likely to be undertaken. Finally, these three typical methods are comprehensively compared in order to give instruction of practical application.
At present, most of the on-line insulation monitoring systems are cable network. They exposed many disadvantage in application, such as complicated wiring, installation difficulties, easily affected by electromagnetic interference. To solve the above problems, a new wireless on-line insulation monitoring system is proposed in this paper. The new on-line insulation monitoring system is based on Bluetooth technology and wireless smart sensor modules which conform to the IEEE1451.5 standard. Hardware design and software design are given in this paper. In the new system, TIM (transducer interface module) is comprised of sensor, Ad7655 and BlueCoretrade4-FLASH Plug-n-Gotrade Bluetooth module. NCAP (network capable application process) is comprised of BlueCoretrade4-FLASH Plug-n-Gotrade Bluetooth module and CAN bus module. The definition of TEDS (transducer electronic date sheet) is presented in detail. The paper also demonstrates security of this system when it is applied in power system. This design has many advantages such as compact structure, anti-interference and easy to install.
The intrinsic permittivity, not apparent permittivity, of semiconducting layers of high voltage cross-linked polyethylene (XLPE) cables imposes a significant influence on the design of partial discharge detecting sensors. It has extremely high permittivity, resulting in a dimensional effect, an embodiment of the difference between the intrinsic permittivity and apparent or measurable permittivity. To investigate this dimensional effect in semiconducting material, a mathematical model is set up in this paper for a capacitor with two rectangular-shaped electrodes in parallel, between which is inserted a semi-conducting sample. First, the expression of the electric field in the semiconducting material is worked out theoretically. Then, the measurable or apparent complex permittivity is expressed as a function of intrinsic permittivity, dimensions of the sample and frequency. Next, five blocks with different dimensions are introduced to study the dimensional effect. The numerical analysis demonstrates that above 10 MHz, samples with different dimensions result in different apparent permittivity or measurable permittivity if experiments are carried out for the samples with the assumed dimensions. This implies that dimensional effects should be considered when accurate intrinsic permittivity of the semiconducting materials is needed.
In recent years, with the increase of voltage grade of transmission line, the proportion of outages because of shielding failure also increases. Therefore, exactly evaluating lightning-withstanding level of transmission line is especially important for system service and stable operation. Considering the randomicity of leader propagation, a lightning stroke simulation model on lightning shielding performance of transmission line was presented, in which the simulation charge method had been applied. Simulation results of this model reflected the general rules of lightning stroke: with the direction of downward leader changing from close to the transmission line to far away from it, the lightning strike aim changed gradually from ground wire to conducting wire, finally the earth. Shielding failure probability and stroke distance to earth, which were calculated by the simulation model, were in accordance with the results of lightning simulation experiment and the stroke distance equation recommended by IEEE. So, the simulation model is reasonable.
Migration from traditional motors to more intelligent motors may be seen as a new motor manufacturing trend. It may be considered as addition of intelligence to the motors, so that the overall package requires no more space, yet is capable of increase in efficiency and working capabilities. In this paper an integral motor with a unique design is proposed to overcome critical issues associated with the motor and its embedded systems. It proposes a compact unit built to operate in arduous industrial environments with optimized power consumption and best practice motor management under different load conditions. Advantages of the proposed Integral motor are compactness of combo motor and drive system with no external cabling/wiring. This motor provides a perfect shielding for least amount of radiated emission. It has an inbuilt filter for EMC compliance and has been designed to provide lower EMC noise for immunity of the internal electronics as well as other neighboring systems.
The new approach for fault identification and classification on extra high voltage transmission line using discrete wavelet transform is proposed in this paper. The sharp variations of the short circuit transient signals generated, which are recorded at the sending end of the transmission line, are adopted to identify the fault. The threshold values involve the fault classification and these are done on the basis of the multiresolution analysis. The results prove that the proposed method is an effective one in obtaining the result within short duration of time by using Daubecheies 4 and 9. Simulation of the power system is done using MATLAB.
Power quality issues are day-by-day becoming important because of increasing use of sensitive electronic equipments. Power quality problem is any power problem manifested in voltage, current or frequency deviations those results in failure or mis-operation of customer equipment. Before connection of a sensitive piece of an equipment to supply system it is essential to assess the compatibility between the piece of equipment and the supply. In any industrial or commercial facility, assured reliable operation and better performance of various equipments requires understanding of all issues, probable problems, their causes and cost effective solutions. Power quality survey helps to define electrical environment with the objectives to determine general levels of power quality. The PQ survey serves as a baseline against which future surveys could be compared to determine power quality trends. In order to mitigate these power quality anomalies a statistical knowledge base of frequency, voltage profiles as a function of time of the day is required. In this paper results of Power Quality survey conducted at various 33 KV industrial sites in Nasik industrial area are presented with conclusions and remedial actions. The results of this work will be very much useful to the manufactures and users of various equipments, Utilities and statutory bodies in India for drafting and implementation of power quality standards, improving the compatibility of electrical, electronic equipments by improving inherent ride through capability with proper design as per the electrical environment.
The art of reconfiguring power distribution system in such a way that it becomes more reliable and flexible is very crucial, but complicated in the presence of distributed generation units such as diesel generator, photovoltaic, and wind turbine. Such a kind of art is presented in this paper as radial and loop distribution system, with dispersed power sources. Energy capacitor system (ECS) is involved as a storage device and playing the main role of load following operation. Utilization of multi agent based operation and control of the system has been used. Information among the c, namely the diesel generator unit and the ECS, is transferred through computer network. Hierarchical control used in this paper in the case of local control on the operation of the ECS. Results showed an improvement in the power quality of the system, in both global and local levels of control.
A simple control of Unified Power Quality Conditioner based on current source inverter for three phase four wire system is presented. The compensation strategy is based on extraction of unit vector template. Reference voltage signals are derived from distorted source voltage with unit vector templates, while current references are derived using Akagi's instantaneous reactive power theory. A simple hystersis band technique is used for derivation of switching signals to inverters. Simulation results, obtaining using MATLAB/SIMULINK under non- linear R-L loading conditions are presented and discussed. It eliminates current as well as voltage harmonics present in the system effectively.
This paper presents the dynamic analysis results of a system event in Thailand power network using a wide-area monitoring system based on synchronized phasor measurement units (PMUs). The salient feature of the proposed monitoring system is the convenient installation of PMU at 220V wall power outlets. The event considering here is a 80 MW load transferring from Thailand to Malaysia systems through a weak 115 kV tie-line. To perform load transferring, a synchronization between both systems is required. This causes a problem of frequency oscillation in a southern area of Thailand. Besides, this event severely excites the inter-area oscillation in a 230 kV tie-line between central and southern areas of Thailand. Analyzed results based on discrete wavelet decomposition and short-time Fourier Transform provide valuable information of the system dynamic behavior in both frequency and time domains.
Recent stabilizer design using wide-area measurement systems (WAMS) signals has been suggested to enhance the dynamic performance of large interconnected power systems. However, there is an unavoidable delay involved before these signals are received at the stabilizer site. Long time-delay may be detrimental to system stability and may degrade system performance. Therefore, the delay-independent robust control problem of large interconnected power systems based on WAMS is studied via H∞ fuzzy control method. First, a set of equivalent Takagi–Sugeno (T–S) fuzzy model is employed to represent the large interconnected power systems. A wide-area state feedback decentralized control scheme is developed to stabilize the T–S fuzzy systems without any wide-area signals delay information such that the H∞ performance is achieved. The H∞ fuzzy robust control design problem is parameterized in terms of a linear matrix inequality (LMI) problem, and the LMI problem can be solved very efficiently using the convex optimization techniques. Finally, the performance of the robust control is studied using a fourteen-machine interconnected power system example.
Proper rating and placing of surge arresters in HV substations is vital for safe protection of the equipment and high availability of the entire power transmission system. However, a substation is a complex system for steep surges, and for many configurations it cannot be said easily whether all parts of the substation are protected sufficiently by the surge arresters installed or not. Computer simulation of lightning surges and their magnitudes inside a substation can help determining the risk of damages of equipment by lightning overvoltages and supports optimized placing and rating of surge arresters.This paper describes typical problems out of the daily practice. It shows the complexity of insulation co-ordination problems with the need for an individual consideration of each substation. Computer based simulations can show the maximum overvoltage stresses at different locations of a substation for different switching conditions and surge arresters provided already in the planning stage. Representative modeling of transient overvoltages will be shown as well as the general way how to carry out such studies. Main input parameters and influencing factors will be discussed showing possible variations to design the transmission system which would reduce overvoltage stresses. Considering the statistical nature of lightning surges helps to define the failure risk at reasonable amount and optimization of the protection devices necessary.
Three-level neutral point clamped (NPC) converters seem to be best suitable for high power and medium voltage applications. However, owing to the special configuration of three-level NPC converters, it's very difficult to design the snubber circuits which are necessary to ensure the appropriate switching conditions for the insulated gate bipolar transistor (IGBT). This paper firstly point out that pulse blocking process is ignored by most snubber circuit designators and introduce new overvoltage problem to the inner IGBTs. Then, detailed discuss the general design principle to avoid these overvoltage problems. Finally, propose an improved McMurry snubber circuit for three-level NPC IGBT converter. Simulation and experimental results demonstrate the validity of the above analysis and the effectiveness of the improved snubber circuit.
Voltage sag is the major power quality problem, which could disrupt the operation of sensitive equipment. This paper presents the applications of instantaneous energy direction for voltage sag source detection. Simulations have been performed to provide the analysis for system with distributed generation units. The studies show that the presented method can effectively detect the location of the voltage sag source.
A new algorithm for automatically generating power-flow diagrams is presented in this paper. Punishing Function method along with Interior Point method is adopted in the algorithm to locate stations on diagrams. Folded Line method is incorporated as well to route and connect. Diagrams generated with this new algorithm are aesthetic and practical. A software system based on this algorithm has been practically applied to the electric network as a part of AEMS system in Shanghai grid, China. The result of three applications with this algorithm, IEEE 14 Buses, IEEE 39 Buses, and the shanghai power grid are presented.
This paper proposes a new method of controller design for damping inter-area oscillations in power system. The concepts of the mode controllability index and mode observability index are introduced into the modal analysis at the operating point in damping controller design. The controller is located according to mode controllability index, and the input signals of controller are selected according to mode observability index. Then a method is presented to obtain the optimal global signals combination under the constraints of the amount of signals. The parameters tuning of the controller is based on phase compensation information. The proposed schemes are validated by eigenvalue analysis of a two-area system. Simulations results also demonstrate the advantage of designed damping controller.
This paper examines the feasibility of applying VSC-HVDC system to improve damping of power swings by utilizing its real and reactive power modulations. The proposed control strategy, based on the nonlinear system model and the energy function analysis, has been derived as well as its implementation with locally available signals. Enhanced system damping property is demonstrated through the simulation results.
