Tomasz Okon

Influence of UPFC device on power system state estimation

The paper presents comparative studies of state estimation for a power system with and without the UPFC device. Weighted least squares state estimation is considered. Such parameters of state estimation are taken into account as: the condition number of the gain matrix, parameters characterizing accuracy of estimation results, and number of iterations in a computational process. During investigation, impact of existence UPFC in a power system on the mentioned parameters of the state estimation is analyzed for different coordinate systems, in which state vector is considered, for different levels of stress of a power system and data redundancy. In the paper, the considered parameters of state estimation are determined for the IEEE 14-bus test system. The results of the analyses show, that in general, impact of existence UPFC in a power system on features of the state estimation is negative, and particularly essential in some cases.

Consideration of different operation modes of UPFC in power system state estimation

Power system state estimation is one of the functions performed in modern control centers. When FACTS devices are in a power system they should be taken into account in state estimation. In the paper, existence of UPFC, i.e. the most universal FACTS device, in a power system is considered. UPFC can operate in different modes. It can operate with full utilization of its possibilities or as SSSC or STATCOM. The aim of the paper is to present results of investigations of features of power system state estimation performed with use of the knowledge about actual operating modes of UPFC. The investigations have been made for the WLS power system state estimation. After the proposed approach to state estimation is outlined the results of the computational investigations are presented. During investigations, such features of the state estimation as conditioning of estimation process, accuracy of results, number of iterations in calculations are analyzed. At the end, conclusion from the carried out investigations are drawn.

Comparison of weighted-least-squares power system state estimation in polar and rectangular coordinate systems

The paper presents a comparative investigations of estimation of power system state in polar and rectangular coordinate systems. The estimation with the use of the weighted least squares method is considered. During investigations, impact of a coordinate system, stress of a power system and a data redundancy on such parameters of a state estimation as: number of iterations, the condition number of the gain matrix and parameters characterizing accuracy of calculation results and reliability of estimation is analyzed.

Properties of indices for voltage stability assessment

The paper deals with evaluation of a power system from the view-point of voltage stability. It is concerned with the indices which are proposed as voltage collapse proximity indicators. In the existing papers, many such indices can be found. In the paper, the so-called line stability indices, defined using the static approach to the study of voltage stability, are taken into account. If the line stability indices are close to 1, a line can be considered to be critical. After the considered indices are described, investigations of correlation of values of the mentioned indices and results of a single-contingency analysis for a power system are presented. The investigations shows, that not always when the branch stability indices are large the outage of the branch is critical, and the outage of a branch can be critical, though values of branch stability indices are low.

Phase shifter models for steady state analysis

Phase shifting transformers are widely used for control of active-power-flows in power systems. Modern variant of phase shifting transformer is (semiconductor-controlled) static phase shifter. All the mentioned devices allow changing phase shift between the voltages at the interconnected busbars. Those devices called as phase shifters play the important role in a power system. The paper deals with modeling of the phase shifter for the aim of steady state analyses such as (optimal) power flow, state estimation. In the paper, after a review of the phase shifters is presented, critical review of their models for steady state analyses is given. For each model, its features are discussed. At the end, attention is paid to the comparison of the considered models.

WLS state estimation in polar and rectangular coordinate systems for power system with phase shifter

The paper presents a comparative investigations of the state estimation of a power system with a phase shifting transformer in the polar and rectangular coordinate systems. The estimation with the weighted-least-squares method using the augment matrix approach is considered. During the investigations, one performs of analysis of impact of a coordinate system, in which the state vector is considered, and data redundancy on such parameters of a state estimation as: the number of iterations, a condition number of a coefficient matrix, parameters characterizing accuracy of calculation results.

Impact of reactive-power optimization on voltages in a power system

The parameters of voltages in a power system are essential element of evaluation of power quality. The paper deals with deviations of voltage magnitudes from the predetermined values. One of the ways of reducing the mentioned deviations is reactive power optimization. At the beginning of the paper, dependence of the voltage magnitude at the end of the branch on reactive power flow on this branch is considered. Proper determination of reactive power flow on the branch enables decreasing the difference between voltage magnitudes at the ends of this branch. Performing reactive power optimization, one can find such reactive power flows in a power system, that nodal-voltage magnitudes are increased and at the same time the difference between maximum and minimum value of nodal-voltage magnitudes in a power system decreases. In the paper, correlation between changes of system active-power loss and a voltage-oriented index, to be effect of the reactive-power optimization, are also investigated. It is evident that for most of the cases of power system operation, that correlation is strong. So, in a reactive power optimization process, the similar voltage effect can be achieved, when the objective function is system active-power loss as well as when this function is the considered voltage-oriented index.

Reactive Power Planning - sequential approach

The paper concerns the problem of the Reactive Power Planning (RPP), being one of the most challenging problems in power system analyses. The authors present theoretical background for the proposed optimization method of RPP from the viewpoint of the economic aspect. If an objective function is the Return On Investment (ROI) in new RPSs in a power system, then solution of RPP ensures the highest efficiency of such an investment. The described method uses the objective function which is equivalent with ROI in new RPSs. To ensure possibly the best features of the optimization procedure, tabu search and the method of interior point are utilized. To determine the possible locations of new RPSs, one utilizes indices of sensitivity of system losses of active energy to nodal reactive powers. Optimization calculations are made for certain period of time. Calculations for separate time points are base for determining sizes of new RPSs.

Possibilities of control of reactive power flow in polish power system

Excessive reactive power flows are an important problem in a power system. Optimization of reactive power flows in the system allows reducing them. This paper deals with optimization of reactive power flows in the national power system. Effects of two variants of this optimization are presented. One of them is when voltage magnitudes at generation nodes, on-load tap changer positions, and reactive powers of compensators, which already exist in a power system, are control variables. In the second variant, one takes into account such control variables as in the first variant and also possibility of injection of reactive power at each node where it is possible. In that way, limit capabilities of modification of reactive power flows in the national power system are determined. In the paper, effects of optimization in each of the mentioned variants are analyzed. Particular attention is paid to comparison of those effects.

A study of operation area for power line with UPFC

The Unified Power Flow Controller is the most advanced device of FACTS family. It is able to control active and reactive power and voltage magnitude simultaneously. A control range of these system parameters is dependent on UPFCs inverter constraints and also on operating conditions of the power system. In this paper, the results of investigations of influence of UPFC constraints and operating conditions of the power system on UPFC control abilities are presented.