Improvements on the line outage distribution factor for power system security analysis

A method is proposed which avoids many limitations associated with traditional B-coefficient loss coefficient calculation. The proposed method, unlike the traditional B-coefficient method, is very fast and can handle line outages. The method utilizes network sensitivity factors which are established from DC load flow solutions, Line outage distribution factors (ODFs) are formulated using changes in network power generations to simulate the outaged line from the network. The method avoids the use of complicated reference frame transformations based upon Kron's tenser analysis. The necessity of data normalization used in least squares and the evaluation of the slope of /spl theta//sub j/ versus PG/sub n/ is not necessary with the proposed method. Using IEEE standard 14-bus and 30-bus systems, the method's results are compared against results obtained from an AC load flow program (LFED). The method's solution speed is compared to that of the LFED method, the base case database method and the conventional B-coefficient method based on A/sub jn/-factor. The proposed method is easy to implement and, when compared to other methods, has exhibited good accuracy and rapid execution times. The method is well suited to online dispatch applications. >

An expert system is developed to determine the steady state security of a power system after a contingency. Line, transformer and generator outages are considered. For any load in the system, overloaded branches are determined by comparing the system load to three load levels closest to the actual system load and using generator shift or branch outage distribution factors. The expert system, in conjunction with the DC load flow, is designed to identify the harmless and harmful contingencies as well as the overload branches. If a contingency cannot be determined as harmless or harmful then an AC load flow is suggested. Turbo-Prolog is used for symbolic manipulations and reasoning. The developed system is applied to a 12 bus power system. The results indicate that the expert system can be used in contingency screening as well as online operation to assist the operator. >

Steady state analysis techniques use linear phasor circuit models, but power flow calculations require the solution of nonlinear algebraic equations. Small-signal linear models form the basis of solution algorithms such as the Newton-Raphson method and decoupled load flows. Since linear models are attractive from the viewpoint of gaining significant insight into system behavior under different operating scenarios, large-signal models such as 'DC models' are commonly employed. Results obtained from linear models are approximate, but they provide easy comparison between different operating conditions. Contingency ranking using a DC model, and generation shift and line outage distribution factors is highly satisfactory in many instances. Studies requiring steady state analysis such as security analysis, optimal power flow and economic dispatch, and voltage stability can significantly reduce computational burdens by assuming linear models. The main objective of this paper is to study quantitatively the relative merits of commonly used linear models in steady state power system analysis. The 'DC model' assumes negligible resistances and flat voltage profiles, and relates the bus phase angles to real power injections. A new linear model which accounts for the voltage and reactive power flows is developed, and compared to the results from 'DC model' and 'small-signal' models. The figure of merit for comparison is taken as the root mean square difference of similar quantities such as bus voltages and line active and reactive flows. IEEE 14-bus is used for the testing. Results show significant potential for the new linear model.

This paper proposes a new sensitivity factor to solve the real-time line flow calculation problem, which is called Jacobian based distribution factor(JBDF). It is derived from the Jacobian matrix of the base case Newton-Raphson load flow solution, and kept constant during real-time line flow calculation. Different from the well-known distribution factors, such as generation shift distribution factor (GSDF), generalized generation shift distribution factor (GGDF) and Z-bus distribution factor (ZBD), it not only reflects the change of each bus injection active power, but also the reactive power. When the loading conditions change from the base case loads, either conforming or non-confirming changes in real and reactive power, it can fast and precisely compute the active line flows without the need of iterations. The proposed JBDF method is tested by IEEE 14-bus system. The numerical simulation results demonstrate that the proposed method is very accurate and fast in computation. It is very suitable for real-time applications.

This paper proposes a new sensitivity factor, Jacobian Based Distribution Factor (JBDF), to solve the real-time line flow calculation problem. It is derived from the Jacobian matrix of the base case Newton Raphson power flow solution, and kept constant during real-time line flow calculation. Differing from the well-known distribution factors, such as Generation Shift Distribution Factor (GSDF), Generalized Generation Shift Distribution Factor (GGDF) and Z-Bus Distribution Factor (ZBD), it reflects the changes of active and reactive power in each bus. When the loading conditions change from the base case loads, either conforming or non-confirming changes in real and reactive power, it can rapidly and precisely compute the active line flows without any iterations. The proposed JBDF method is tested on the IEEE 14-Bus System. The numerical simulation results demonstrate the proposed method is very accurate and rapid in computation. It is highly suitable for real-time line flow calculation.

This paper is based on a linear contingency analysis program that computes line flow changes and bus voltage changes resulting from branch outages and generation changes. A modern formulation has been adopted based on the relation V=IZ. For maximum speed in processing large number of contingencies, line (branch) outage distribution factors are computed and stored through separate small program. Besides retrieval of these factors and reading of relevant data, the main program is also capable of calculating these factors using elements of bus impedance matrix (Zbus) and branch impedances. The computer language used for contingency analysis program is BASIC 5.1 codeable on Hewlett Packard computer. The language is very fast, comprehensive and powerful to code scientific programmable instructions and is combination of FORTRAN-77, PASCAL and BASIC P.C. based language. The resulting program processes single to four branch outages at a time for 50 buses WAPDA 'S 500/220 kV primary transmission system for 119 branches along with generation changes at 17 buses for 102 generating units in about 1.89 seconds on a Hewlett Packard Management Computer. 1.2.3

An Efficient Methodology for Study Mode Security Assessment of Power Systems for Large Disturbances

Line outage distribution factors (LODFs) are utilized to perform contingency analyses in power systems. Since each contingency requires separate LODFs, a quick calculation of LODFs, especially with multiple-line outages, could speed up contingency analyses and improve significantly the security analyses of power systems. This letter provides two direct proofs for expressing LODFs in terms of power transfer distribution factors (PTDFs) of pre-contingency network. Simple matrix calculations are required in the proposed approach for a fast evaluation of LODFs.

Power system security is a major concern in real‐time operation. It is essential to protect the system from blackout by taking proper control actions. This study proposes a boosting algorithm for the precise and accurate prediction of static security assessment of power systems using synchronised measurements. In addition to security status, the proposed approach also predicts the type of violations which may be either line overload/voltage violation or both of the insecure operating conditions. To overcome the computational complexity, the number of input phasor measurements is reduced by a statistical approach based on class separability and correlation coefficient indices. In the classification stage, support vector machines (SVMs) are used as weak classifiers and a strong classifier is constructed as the linear combination of many weak SVM classifiers. The performance of the Adaptive Boosting (AdaBoost) algorithm is further improved by a new weight updation strategy using fuzzy clustering thresholding technique. The efficiency of the proposed approach is demonstrated on IEEE 14‐bus, IEEE 30‐bus, and Indian 246‐bus systems. Further, the test results reveal that the proposed method of security assessment performs better than the other traditional classifiers viz. SVM, feed forward neural network and k‐nearest neighbour classifier.

SCALE: A hybrid MPI and multithreading based work stealing approach for massive contingency analysis in power systems

On-line economic dispatch using a new loss coefficient formula

In this paper, a knowledge-based system for static security assessment of power system is proposed and investigated. An expert system (ES) for screening the consequences of transformers' and electrical lines' single outage was developed. The rules derived from a simulation model, irrespective of the size of the power system, are thus obtained. A dedicated artificial intelligence language (Prolog) for rules implementation was used to build the ES named CONTIG. The results show that such ES can be very effective for contingencies' selection. The benefits for a moderate size power system (25 buses and 30 branches) were analyzed using CONTIG. This approach has a great potential for online application

In this paper, analysis and ranking of single contingency due to the outage of transmission lines for a large scale power system of the Kurdistan Region (KR) are presented. Power System Simulator software (PSS®E33) is used to simulate the Kurdistan Region power system network and perform the contingency analysis for single line outage. This analysis is essential in order to predict and evaluate the voltage stability in case of contingency occurrence to know the most severe case and plan for managing it. All possible transmission line outages of the network are tested individually. After each branch disconnects, load flow analysis are applied by using Newton Raphson method then all bus voltages are recorded, and compared with them before the contingency. Voltage performance index is calculated for all possible contingencies to rank them according to their severity and determine the most severe contingency which is corresponding to the highest value of performance index. Also, the contingencies which cause load loss and amount of this load are observed.

In this study, it is proposed to carry out an efficient formulation in order to figure out the stochastic security-constrained generation capacity expansion planning (SC-GCEP) problem. The main idea is related to directly compute the line outage distribution factors (LODF) which could be applied to model the N — m post-contingency analysis. In addition, the post-contingency power flows are modeled based on the LODF and the partial transmission distribution factors (PTDF). The post-contingency constraints have been reformulated using linear distribution factors (PTDF and LODF) so that both the pre- and post-contingency constraints are modeled simultaneously in the SC-GCEP problem using these factors. In the stochastic formulation, the load uncertainty is incorporated employing a two-stage multi-period framework, and a K — means clustering technique is implemented to decrease the number of load scenarios. The main advantage of this methodology is the feasibility to quickly compute the post-contingency factors especially with multiple-line outages (N — m). This concept would improve the security-constraint analysis modeling quickly the outage of m transmission lines in the stochastic SC-GCEP problem. It is carried out several experiments using two electrical power systems in order to validate the performance of the proposed formulation.

This study proposes an adaptive boosting (AdaBoost) algorithm for precise and accurate prediction of transient security assessment of power systems using synchronised measurements. The proposed approach (PRPA) also determines the generator coherent state as well as the synchronism status of each generating unit. The PRPA consists of three classifier models, in which classifier I determines the transient security status and classifier II is used to determine the generator coherency. Classifier III is a hybrid classifier, which determines the individual generator synchronism state for a given operating condition. This hybrid classifier consists of an array of parallel classifiers, where one classifier is assigned to each generating unit of the power system. For this assessment, the measured rotor angles of the generators are used as inputs to the proposed classifier models. In classification stage, several weak classifiers are combined in a linear manner to construct a strong classifier. The performance of the AdaBoost algorithm is further improved by a new weight updation strategy using fuzzy clustering thresholding technique. Simulation results obtained from IEEE 14‐bus, IEEE 30‐bus and Indian 246‐bus systems reveal that the PRPA can enhance the overall monitoring and assessment of power system using synchronised measurements.