Jan Švec

Evaluation of IRP, FBD, SD, and generalized non-active power theories

Most of modern power equipments connected to the grid must be viewed as non-linear loads producing voltage and current harmonics, subharmonics, and quasi-periodic and stochastic disturbances even under normal operation conditions. An analysis and comparison of usage of different power theories for the parallel compensation of periodic and non-periodic disturbances is presented in the paper. Different reference voltage vectors and averaging time intervals are applied in the power theories.

Cooperative Control of Active Power Filters in Power Systems without Mutual Communication

The procedure for calculating controller parameters of the APFs implemented into a multibus industrial power system for harmonic voltage mitigation is presented. The node-voltage-detection control strategy is applied and the basic controller parameters are found under the condition that the demanded THD factors at the buses where the APFs are placed will be obtained. A cooperative control of several APFs without mutual communication is proposed, simulated, and experimentally verified. By tuning the controller gains without considering the power circuit parameters, all APFs used tend to share harmonic load currents approximately equally regardless of the operation modes of the nonlinear loads in different parts of the power system.

Comparative review of reactive power compensation technologies

The quality of electrical power in a network is a major concern which has to be examined with caution in order to achieve a reliable electrical power system network. Reactive power compensation is a means for realising the goal of a qualitative and reliable electrical power system. This paper made a comparative review of reactive power compensation technologies; the devices reviewed include Synchronous Condenser, Static Var Compensator (SVC) and Static Synchronous Compensator (STATCOM). These technologies were defined, critically examined and compared, the most promising technology is recommended for the realisation of an effective, efficient, sustainable, qualitative and reliable electrical power network.

FACTS devices influence on power losses in transmission systems

Since there are still higher efforts for transmission systems equipment utilization, more control mechanisms and devices are integrated to the systems and their dispatch centers and these will be also in future. FACTS devices purpose is preferably to maintain voltage levels and to control active and reactive power flows. Their implementation in the grid can result from the necessity to improve the system capabilities in a long-term period or to solve some extraordinary states. The paper deals with the implementation of shunt and series FACTS devices into electrical transmission systems and their influence on active power losses. There are provided comparison analyses of how different FACTS types have a potential to changes power losses in the system either in a negative or in a positive way. There are explained basic principles and the results are presented on the IEEE/CIGRE transmission system model.

Synchronous phasors monitoring system application possibilities

The paper deals with some tasks of advanced methods to achieve security and reliability of transmission power systems. There are discussed advanced principles and techniques in monitoring systems. The paper main part is devoted to possible applications of PMUs (Phasor Measurement Unit) and their integration into WAMPaC systems (Wide Area Monitoring, Protection and Control). Significant transmission system states were analyzed in several case studies. PMUs utilization for voltage monitoring is demonstrated for three cases - standard system state, high-load state and islanding. Here the attention is paid to the possibilities of power system observability improvement using measuring chain error elimination. Other possible applications in transmission systems include ampacity determination of transmission corridors, the calculation of line electrical parameters using synchrophasor measurement, state estimation issues and power system stability. The power system model was established for methods and algorithms verification purposes. The appropriate algorithms and their parameters were found using simulation outputs to create the local automatics, e.g. Automatic Power System Stabilizer (PSS).

Using renewable MV wind energy resource to supply reactive power in MV distribution network

This paper deals with the use of Medium Voltage (MV) renewable wind energy source to optimize reactive power in a distribution network, it describes the increase of power factor when the reactive power is controlled at a wind farm increase in power factor allows improvement in the stability of distribution networks, and the increase in power factor is used as new methodology to reduce power losses, Matlab/Simulink program is used to show the results of the analysis.

Advantageous positioning of wind turbine generating system in MV distribution network

This paper presents a new method for achieving voltage stability and reduction of power losses with renewable wind turbine generating system (WTGS) installed at different position on a Medium Voltage (MV) distribution system. The proposed network is a three-phase system consisting of 0.4 kV low voltage (LV) feeder with an active power (P) of 8 MW and a negative VAR (Qc) of 0.5 MV AR. And a 20 kV MV feeder with an active power (P) of 22 MW and a negative VAR (Qc) of 1.5 MV AR. The 0.4 kV and 20 kV feeders has varying positive VAR values of 2, 2.25, 2.5 and 6, 6.5, 7 MVARs respectively. Three sets of datas were observed; data 1, 2, and 3, the feeders are connected to a 20 kV MV distribution network, which is then linked to a 20 kV substation. Thereafter, a 20 kV MV renewable WTGS energy source with IGBT converters is integrated to the network for effective reactive power compensation. Three different Cases have been analyzed; First is the case with the proposed power system network analyzed without any WTGS attached to the network, in other words when the WTGS is switched off (this is designated as Case 1). Second is the situation with the WTGS positioned at the terminal end of the 20 kV MV distribution network (point 1, which is designated as Case 2) and Third is the situation when the position of the wind energy source is changed and stationed at the beginning of the terminal of the 20 kV MV power line (point 2, which is designated as Case 3). Matlab/Simulink software is used for the simulation of the system model. Simulation results for each of the case studies is analyzed and it is observed that research findings for Case 2 is more efficient in achieving improved voltage stability and power losses reduction in medium voltage electric-power distribution network.

Protection settings optimization in distributed generation system

This paper deals with protection problems in distributed generation systems, it summarizes the protection methods known so far, and it proposes a new protection scheme usable for these systems. First, brief comparison of protection concepts of classical and distributed generation systems based on overcurrent protections is performed, and individual differences in protection settings are discussed. New setting algorithm, based on optimization of appropriately designed objective function, and adaptive directional overcurrent protections with inverse-time characteristics, is performed. Next, validation of proposed optimized setting in SimPoruchy 2.1 program was performed. The software allows for quick and well-arranged output of failure currents in the system and also for simulation of directional protections with inverse-time characteristics used in the model.

STATCOM effect on voltage stability in Ghanaian electrical grid

This paper deals with using STATCOM for voltage stability purposes which is analyzed on the Ghanaian power system development. Preliminary studies have shown that the northern sector is vulnerable to voltage instability which has led to the proposed installation of STATCOM in a key substation Tamale. It is therefore necessary to assess the performance of the device when put in operation. Comparison had therefore been made between the use of STATCOM and a fixed compensator. Line and generator contingencies as well as small signal disturbances analysis have been carried out. Voltage stability is improved with the installation of STATCOM but do not affect the interconnection between Ghana and Burkina Faso. Further evaluation focused on the inter-tie is proposed.

Nelder Mead method used in protection setting optimization

The paper deals with distributed generation network protection based on adaptive directional overcurrent protections with inverse-time characteristics. Correct setting of all protections is performed by minimization of appropriately designed objective function. The shape of inverse-time characteristics is described by time multiplicator and slope constant. Since optimization of slope constants is not a convex problem, classical gradient optimization methods are not suitable. As a possible solution a direct search algorithm can be used. For this purpose, Nelder-Mead simplex algorithm is used in the article. Convergence speed of the algorithm is highly dependent on proper initial estimations, and hence optimization process consists of two parts. In the first part, simplified objective function only is used to obtain initial estimations. In the second part, full objective function is used to obtain final coefficients. Next, validation of proposed optimized setting in SimPoruchy 2.1 program was performed. The software allows for quick and well-arranged output of failure currents in the system and also for simulation of directional protections with inverse-time characteristics used in the model.