Vedran Kirincic

Transmission line impedance estimation based on PMU measurements

State estimation is one of the most important network management functions, responsible for determining the actual state of the power network based on the network model, available telemetry (analog measurements and digital device statuses) and pseudo measurements. Phasor measurement units (PMUs) provide valuable instantaneous information regarding power system stability and security, and thus have the potential to improve the reliability of the state estimator. Also, measured synchrophasors can be used for transmission line impedance estimation, which results in more accurate power system state estimation, in comparison with the traditional approach that uses catalogue values of the transmission line impedance.

Transmission line positive sequence impedance estimation based on multiple scans of Phasor Measurements

In the paper the proposed algorithm for estimation of transmission line parameters is tested and evaluated. The proposed algorithm uses the weighted least square method with multiple scans of measurements derived from Phasor Measurement Units (PMUs). The network topology and loading conditions in the transmission network change continuously, which can influence the estimation of transmission line parameters with synchrophasor measurements. The case studies in the paper assess the influence of usage of multiple scans of synchrophasor measurements during sudden change of loading and network topology conditions. In the paper the presented algorithm is tested using simulated PMU measurements with and without introduced random errors. High number of measurement scans improves the transmission parameter estimation results but at the same time the calculation time of the algorithm increases. To obtain the optimal results, a compromise between the number of measurement scans and calculation time is needed.

Automated control for Power Transmission System in urban area

Modernization of a power system involves development and deployment of an Intelligent System or a System Integrity Protection Scheme for a Power Transmission System. As the observed urban Power Transmission System has a ring topology, including overhead lines and underground cables, various scenarios of a closed loop and island operation are considered. Deficiencies of a traditional control solution are stated and a modern automated control of the urban transmission system, based on synchronized phasor measurements, is presented. A developed architecture is designed to provide real time monitoring and control functions. Control actions are based on different switching and operational states.

A dual-axis tracking photovoltaic power plant as an educational tool

Renewable energy sources have become a considerable part of electric transmission networks as well as medium and low voltage distribution networks. Understanding the overall process from design stage up to the installation stage, followed by the commissioning and startup of renewable energy sources plants is essential knowledge that electric engineers nowadays should posses. Therefore, in the first part of the article activities, conducted at the Faculty of Engineering, University of Rijeka, Croatia, necessary for the installation of a fully operational, grid connected photovoltaic power plant with dual-axis tracking system have been described. Consequently, upon photovoltaic plant’s installation and commissioning, students are able to have ‘hands-on’ on a fully functional photovoltaic power plant and perform supervised, ‘live’ measurements and compare it with previously calculated values. Therefore, new – dedicated laboratory sessions have been introduced in an existing subject to make the most of the photovoltaic installation in the teaching process. In the second part, the article is mainly focused on the newly introduced laboratory sessions as well as on the educational framework and methodology. Some of the experiments that our students are able to perform include alternating current and direct current operating values measurements (photovoltaic string and inverter voltages, currents, power, efficiency, etc.), environmental parameters measurements (irradiance, air temperature, wind direction, velocity, etc.) and grounding parameters measurements (soil resistivity, photovoltaic plant’s grounding resistance). The acquired knowledge gained from the activities performed during our educational photovoltaic plant project realization give us the ability to propose a methodology that can be used as the key model for other universities and faculties.

A noninvasive inclusion of synchrophasors in the power system state estimation

Original scientific paper The paper investigates the application of synchronized phasor measurements, which are available from Phasor Measurement Units (PMUs), in the power system state estimation. In order to avoid changes in the type of the input measurements of the classical state estimator, which runs in the control centre, the proposed model utilizes voltage and current phasors to calculate pseudo-measurements such as pseudo-voltages, power flows and power injections. These pseudo-measurements are used together with the voltage phasor magnitudes and the conventional measurements in the iterative procedure. The IEEE 14, 30, 57 and 118 buses test systems as well as the mathematical model of the Croatian transmission power system were used as the test systems. The results of the simulation were compared with the classical state estimator, which uses only conventional measurements. The effect of the voltage phasor angles on the state estimator performance was investigated.

A Synchrophasor Assisted Hybrid State Estimator

Abstract The paper presents a Synchrophasor Assisted Hybrid State Estimator that utilizes the conventional SCADA measurements and the synchrophasors obtained from Phasor Measurement Units (PMUs). To take advantage of the high sampling frequency of the multiple sets of synchrophasors they are preprocessed in a recursive algorithm that provides the state estimate for the power system part observable by PMUs. The results are forwarded to an iterative procedure in which they are combined with SCADA measurements. The given solution was applied on the IEEE test systems with 14, 30 and 57 buses and its performance was compared with other state estimators. The filtering of measurement errors and convergence, while providing improved accuracy of the final state estimates of the developed methodology can be compared with other hybrid state estimators.

The effect of branch parameter errors on voltage stability enhancement schemes

Branch parameter errors may affect the success of voltage stability enhancement schemes. This work considers errors of varying sign and magnitude in the parameters of transmission lines. The considered voltage stability enhancement scheme is based on a central state estimator and on a distributed monitoring of individual lines. The state estimator incorporates synchronized phasor measurements. The applied voltage stability enhancement scheme is based on monitoring individual branches and on load shedding, for various thresholds of the applied stability indices. A discussion on voltage stability enhancement schemes and branch parameter errors is followed by simulations on two case studies involving two IEEE studies and both static and transient contingencies. In conclusion, dealing with branch parameter errors in the context of voltage stability enhancement schemes is discussed.

The Effect of Branch Parameter Errors to Voltage Stability Indices

Errors in the values of network parameters stored in the control center may affect the important application of voltage stability monitoring. This paper investigates the effect of branch parameters errors to voltage stability monitoring, using the state vector obtained by the state estimator. In particular, the state vector is used for calculating a voltage stability index that indicates the most critical branch (the one that first reaches its active power transfer limit). The states of the power system are estimated under various scenarios of possible errors in the reactance of the critical branch and then are used for the calculation of the voltage stability index. The case studies are performed using the IEEE systems with 14 and 39 buses and it is shown that the calculated value of the stability index depends on the error in the branch parameters, the power system structure and the contingency leading to voltage instability.

System Integrity Protection and Control based on Synchronized Measurement

The paper presents a control system solution based on synchronized phasor measurements for the urban area transmission system. Specificity of the analyzed system is a highly meshed overhead and cable sections network, with two city power plants, providing the citys district heating and electricity supply. The mathematical model for static and dynamic analyses of various scenarios was build and verified using measurements from originally developed and deployed portable hand-held phasor measurement units. The control system architecture and functionalities as well as developed control actions algorithms are given, focusing on island operation of the issued transmission system, as the city power plants are capable to supply the critical consumers.