the boundary networks of coherent machines. A spanning tree search algorithm is used to find all combinations of stable islands. The method works quite fast and is suggested for real time calculation. The first step is to calculate the interarea modes of the system as well as clustering the network machines and buses in different coherency groups as primary islanding strategy. The second step of the splitting strategy is a minimum spanning tree based breadth first search algorithm is used to balance and minimise the net flow between the islands tie lines. A powerflowtracing method is applied to ICI in  to determine the domain of each generator. An initial splitting boundary based on grouping information of generators on the graph model is found. The initial splitting boundary is then refined to find the final splitting boundary. The method is based on two principles: 1, coherent groups of generators should be determined and should be in the same island. 2, the reduction of generation load imbalance in each island reduces the amount of load shedding to be done. Powerflowtracing is used to determine how much active power a load node receives from a particular generator node, and a load node can be designated to the generator node. The generator node and its designated load nodes form the domain of that generator node. The initial splitting boundary is a coarse one. After the system loses stability, according to grouping information, the initial splitting boundary search is executed on the graph model with domains of various generator nodes determined with all nodes in some domain. The edges whose incident nodes are in two different domains are found and if the generator nodes in the two domains are asynchronous, this forms the initial splitting boundary. The initial boundary may provide islands with unacceptable imbalance and assuming a reasonable splitting boundary is located between asynchronous generators, the reasonable splitting boundary must be near the initial splitting boundary. Consequently, the reasonable splitting boundary can be found from the initial. A neighbourhood of a load node v is the union of the islands in which at least one of the load nodes is adjacent to v. Such nodes can then be moved into their neighbouring areas. By moving the node which can minimise the imbalance the most, the system is recalculated as well as the neighbourhood nodes. This is repeated until the unbalance degree can no longer be reduced. It is a very fast method, for the 118 bus system, for two cases, the solution was achieved in less than 10ms. However, it was stressed that the post-split conditions could be unstable and would rely heavily on corrective control. This was verified in  where the method was tested to make the generation load imbalance is small as possible.
In this paper, three methods are used to solve the congestion management problem using firefly algorithm with the objective of minimum rescheduling cost. The first method (method - 1) considers all generators in the particular area for rescheduling. In the second method (method - 2) generators are selected based on Generator Sensitivity Factors (GSF) and their outputs are rescheduled optimally using FF algorithm to relive overload in transmission lines. The third method (method - 3) employs powerflowtracing approach to identify the most contributed generators to the congested line and only these generator outputs are rescheduled using FF algorithm to alleviate congestion. In this paper, congestion due to different line outages, generator outages and wheeling transactions are considered. The proposed method is tested on two test systems and the algorithm is validated by comparing the results with DE method.
This paper proposes a methodology to analyze the fre- quency transient process of every generator. The method combines the powerflowtracing algorithm with the kinetic energy theorem of power systems, to obtain the frequency influencing factors of every generator. On the basis of that, it can quantify the contribution of the mechanical power of the generators, the load power and the transmission losses for the frequency deviation. The improved under frequency load shedding strategy is then designed according to the proposed methodology. The simulation results show that the proposed strategy is adaptive to different faults. The proposed strategy can determine the load bus to be curtailed and is more bene- ficial for the frequency recovery when compared with the conventional schemes.
The stability analyses of the rapid increase in complexity of modern power systems require the development of efficient and robust numerical methods. In terms of small signal stability analysis, power systems are usually mod- eled by systems of differential-algebraic equations with large nonlinear dynamics. Simulation in frequency do- main of the resulting dynamical systems heavily relies on numerical methods for eigenvalue problems and systems of linear equations. Direct application of conventional methods (e.g., QR method) for power system eigenvalue problems is computationally not feasible or inefficient. Thus, many special intensive researches for the small signal stability analysis of power systems have been proposed in the last two decades, which devoted to eva- luating a selected (critical) subset of eigenvalues associ- ated with the complete system response.
In the developed world, peoples demands are increasing rapidly. The main problem is to find appropriate ways of supplying the consumption centres with the goods that are produced in distant production units. The main criteria are the preservation of the quality of the transacted goods and the minimization of the transmission losses, and both of these are affected by economic aspects, such as minimising costs. In an attempt to solve these problems, mankind has built transmission networks, such as pipelines, gas networks, heat networks and electrical power networks. At first sight the question of which producer supplies a particular consumer seems to be very trivial, but nowadays, with rapid developments, transmission networks are becoming more sophisticated, i.e. more complex, meshed and widespread. In this paper a new network-flow-tracing method is presented. The major goal of this new method is to define flow paths from producers to consumers across a network. In the past a few methods were already proposed; however, this method is based on a matrix calculation. Although it considers the transmission losses, it is still very simple to understand and also very fast. The new approach was tested on the New England test power system. Since all transmission systems have some common characteristics, knowledge from one engineering field could probably be used in other fields. The idea is to spread the knowledge and to find some of the basic principles of observed phenomena that will enable us to solve problems in a proper manner. In this way, a better insight into the system operation and control can be obtained, especially nowadays when deregulation and liberalization of transmission systems are being introduced.
The powerflow problem is one of the basic problems.Here, load powers and generator powers both are given.On the contrary, optimal powerflow problem some adjustments are made according to some specified criteria for generated power bus voltage etc.In this case, generating cost should be the minimum.It can be determined that the voltages at nodes where the loads are supplied along with the input power.Mathematics is more needed in optimal powerflow problem.Here we have some limits of voltage, power beyond which we cannot let the output go because violation of those limits,fault will be occurred and the system will become damaged.
Experiment A7 was monitored simultaneously by both automated fluorescence detection and manual water sam- pling in both major proglacial outlets. Manual sampling re- vealed dye emergence in only the southernmost, less turbid proglacial outlet. The dye breakthrough curve derived from the analysis of water from manual sampling was in accor- dance with that from automated detection in terms of the general breakthrough curve form and the time of peak con- centration, but was characterized by much-increased noise and increased dye concentration. This is likely due to turbid- ity, which is not corrected for in manual sampling, causing increased scattering of light resulting in unrepresentatively high concentration readings. Imperfections in the sampling bottles and cuvettes used to analyse manual water samples can also introduce error into measured dye concentrations. The breakthrough curves of experiment A7 represent melt- water flow from as close to the pollution source zone as was possible with the prerequisite of flowing water for dye injec- tion. Both curves reached their peak ca. 14 h after injection, after ca. 12 h with no dye signal (in the case of automated de- tection). The residence time, form of the breakthrough curves and emergence of dye in only the less turbid proglacial out- let indicates temporary storage followed by a rapid release of meltwater, with limited interaction with sediments at the bed. 4.4 Throughflow velocities
Abstract — In this paper a circuit model for IPFC is developed using series coupling transformers and comparison of active and reactive power of Transmission Lines with and without IPFC is presented using the proposed circuit model. Comparison is also done with individual Static Synchronous Series Compensators (SSSCs), one on each line of a two line system and the results are compared with the previous one. MATLAB with Simulink and SIM POWER SYSTEMS tools are used for simulation of Transmission lines and IPFC in open loop and closed loop configurations. A common DC link within the IPFC is able to facilitate real power transfer among the lines of the transmission system. Also each inverter can provide reactive power compensation independently.
characteristics of power ﬂow and allow insight into energy dissipation mechanisms of the system. The proposed theoretical mathematical model describes the time- averaged power ﬂow in terms of system’s damping and velocity response (equation (3.6)), which straightforwardly reveals vibration energy dissipation mechanisms of a dynamic system. Furthermore, in the deﬁned power ﬂow space, the time-averaged power ﬂow is represented as the sum of all independent mode power components (equation (3.11)). A power ﬂow bound theorem is proposed to approximate the upper and lower bounds of the time-averaged power. Regardless of the complexity of the dynamic system, its total time averaged power dissipation P=j V ~ j 2 , as deﬁned in equation (3.16), is bounded by one half of the lowest and highest characteristic- damping factors. This average is determined only by the damping properties of the system and is independent of any external excitations, the distributions of stiffness and mass and responses of the system.
In this paper, a comprehensive analysis on the use of ES for reducing power imbalance in a three-phase system is presented. It provides a new theoretical platform to work out the precise control strategy and analytical solution for a series- type three-phase ES in order to reduce both zero-sequence and negative-sequence currents in an unbalanced power system. Under certain conditions, this method can reduce system power imbalance without requiring real power from the ES. Beyond such conditions, the theory can pinpoint the precise condition at which the minimum active power is required from the ES to restore power balance. Therefore, the battery storage on the DC link of the ES can be minimized. Simulation and experiment results obtained from a 3-kW prototype are included to validate the proposed method.
The series inverter is controlled to inject a symmetrical three phase voltage system (Vse), of controllable magnitude and phase angle in series with the line to control active and reactive power flows on the transmission line. So, this inverter will exchange active and reactive power with the line. There active power is electronically provided by the series inverter, and the active power is transmitted to the dc terminals. The shunt inverter is operated in such a way as to demand this dc terminal power (positive or negative) from the line keeping the voltage across the storage capacitor V dc constant. So, the neutral power absorbed from the line by the UPFC is equal only to the losses of the inverters and their transformers. The remaining capacity of the shunt inverter can be used to exchange reactive power with the lines to provide a voltage regulation at the connection point.
Power distribution systems have different characteristics from transmission systems ,.They are characterized as Radial/weakly meshed structures, Unbalanced networks/loads: single, double and three phase loads, High resistance/reactance(R/X) ratio of the lines, Extremely large number of branches/nodes, Shunt capacitor banks and distribution transformers, Low voltage levels compared with those of transmission systems and distributed generators.. Because of the inherent unbalanced nature of the power distribution system, each bus may be having loads that can be three- phase grounded wye or ungrounded delta connected, two-phase grounded or single-phase grounded . The unbalanced nature of power distribution systems requires special three phase component and system models . The operation and planning studies of distribution system requires a steady state conditions of system can be obtained from the load flow solution,.The efficiency of the entire process depends heavily on the efficiency and capability of the load flow program used for this purpose.
In recent year the technology is advances so that transmission network reliable and easy to design. There are many technologies in interconnected power system such as, HVDC and EHVAC. On other side as power system network grow, the interconnected network become increasingly more composite to operate and system can be less protected for riding through the major outages. The power system interconnected network of today is large and complex. There is widely use of microelectronic, computers and high speed communication for control and protection of present interconnected system. The main purpose of FACTS is to improve system controllability and to increase power system bound by using power automated devices. Generally, FACTS devices are more expensive than HVDC devices. In case study consists of 3 generators nine bus system having three load and three transformer. The single line diagram of nine bus system as shown in fig. 1.It is simple diagram of power system to analyzed dynamic behavior and also power oscillation damping. In this system three phase fault is occurs at bus 8.Duration of fault time is 4 to 4.1 sec. After 4.1 sec. the fault is remove system try to maintained stability, also active power, reactive power and bus voltage of different buses is calculated.
An optimal powerflow (OPF) consists of solving equations which characterize an electrical power system (ac- tive and reactive power of each node) adjusting the control variables values (voltages or powers) in order to op- timize a specific system parameter, represented by one target function . A system usually includes state va- riables (unknown quantities) and independent variables (unknown data). Control variables can be any of the in- dependent variables in the system, and are selected depending on the purpose of the analysis.
The post-contingency interface flow limits are in- cluded in the OPF. If all n-1 contingencies were consid- ered, there would be a constraint for each line contin- gency for each interface. This would make the problem size too large for efficient computation. To limit the number of constraints, the OPF is solved without con- tingency constraints, a contingency analysis is per- formed, and then the OPF is resolved with new con- straints added only for those contingency outages that result in overloads, and only for the interfaces that are overloaded.
Although the UPFC and the IPFC have superior capability to control powerflow, there is no commercial application currently. The main reasons are the first concern with combined FACTS is cost. Typically, a FACTS cost around 120-150 $ per KVA, compared to 15-20 $ per KVA for static capacitors. One of the reasons for the high cost is that the ratings of FACTS devices are normally in 100 MVA, with the system voltage from 100 kV to 500 kV. This requires a large number of power electronic switches in series and parallel connection. To provide voltage isolation, 3-phase high-voltage transformers are essential; furthermore, the series-connected transformers require an even higher rating to handle fault voltages and currents. Secondly, as the FACTS devices are installed at different locations for different purposes, each of them is unique. As a result, each FACTS device requires custom design and manufacturing, which leads to a long building cycle and high cost. A FACT is a complex system, and requires a large area for installation and also well-trained engineers for maintenance.
Abstract Optimal powerflow (OPF) is the central optimization problem in electric power grids. Although solved routinely in the course of power grid oper- ations, it is known to be strongly NP-hard in general, and weakly NP-hard over tree networks. In this paper, we formulate the optimal powerflow problem over tree networks as an inference problem over a tree-structured graphical model where the nodal variables are low-dimensional vectors. We adapt the standard dynamic programming algorithm for inference over a tree-structured graphical model to the OPF problem. Combining this with an interval discretization of the nodal variables, we develop an approximation algorithm for the OPF prob- lem. Further, we use techniques from constraint programming (CP) to perform interval computations and adaptive bound propagation to obtain practically efficient algorithms. Compared to previous algorithms that solve OPF with op- timality guarantees using convex relaxations, our approach is able to work for arbitrary distribution networks and handle mixed-integer optimization prob- lems. Further, it can be implemented in a distributed message-passing fashion that is scalable and is suitable for “smart grid” applications like control of dis- tributed energy resources. We evaluate our technique numerically on several benchmark networks and show that practical OPF problems can be solved effectively using this approach.
The response of a PV cell at different light energy figure (1). Shows that irradiation has a significant effect on the current open-circuit. That is the curve of the I-V characteristic and relatively horizontal, while the effect on the voltage in open circuit, i.e. the slope of the I-V curve and relatively vertical, which is quite low-. With regard to the maximum power of a photovoltaic cell, when the illumination is highest, the cell generates more power. The temperature has a very important effect on the open circuit voltage and a no remarkable effect on the short circuit of cell ( Fig. 2).
ABSTRACT: Powerflow analysis is the backbone of power system analysis and design. They are necessary for planning, operation, economic scheduling and exchange of power between utilities. Powerflow analysis is required for many other analyses such as transient stability, optimal powerflow and contingency studies. The principal information of powerflow analysis is to find the magnitude and phase angle of voltage at each bus and the real and reactive power flowing in each transmission lines. Powerflow analysis is an importance tool involving numerical analysis applied to a power system. In this analysis, iterative techniques are used due to there no known analytical method to solve the problem. This resulted nonlinear set of equations or called powerflow equations are generated. This paper presents anew and efficient method for solving the load flow problem of a distribution system. It is mainly based on network topology, basic circuit lawsand power summation technique. The main contribution of this paper is: (i) proposing a new and efficient load flow method for radial and weakly meshed distribution systems,(ii) evaluating the impact of load models, different X/R ratios, load growth and tolerance levels,(iii) analysis of impact of number of loops on weakly meshed distribution systems, (iv) comparison of radial and weakly meshed distribution system. The results are obtained for voltage profile, total power losses time of computation, and number of iterations. Computer program coded to implement this powerflow solution scheme in MATLAB and successfully applied to several practical distribution networks with radial and weakly meshed structure. Effectiveness of the proposed load flow method has been presented on IEEE 33bus and IEEE69 bus radial and meshed distribution networks.