1,721,023 research outputs found
A Basic AC Power Flow Based on the Bus Admittance Matrix Incorporating Loads and Generators Including Slack Bus
Full text linkThis paper presents an algorithm for solving the AC basic power flow based on some enrichments provided in the bus admittance matrix methods findable in the literature. In particular, the interpretation of the slack bus generator as a current source rather than a voltage one and its inclusion inside an 'all-inclusive' admittance matrix allows obtaining strong performances of the algorithm. In fact, this method gives both a well conditioning of the admittance matrix and the reduction of matrix partitioning for each iteration. As a result, a greater precision of the solution, a shorter execution time compared to classical commercial methods, a decreasing number of iterations and optimal convergence properties are obtained. Eventually, in order to show the efficiency of the method, real and fictious networks are tested, by comparing its results and performances with robust open source/commercial software packages that use well-known methods (i.e., Newton-Raphson and Fast Decoupled Load Flow methods)
Some meaningful examples of sequence theory use limitation
No full textSequence theory [1] is one of the most important tool for power system engineers. In fact, both in planning and operating activities, power flow and short circuit studies are always based on the knowledge of the sequence impedances.
Consequently, positive, negative and zero sequence impedances are the first step for power flow and short circuit analyses and are also necessary for setting the distance relays.
Notwithstanding, it is also true that by considering the physical reality of the power networks, it can be questionable to assume purely three-phase configurations and perfectly symmetrical ones, so to use sequence theory based modelling.
It is worth remembering that the use of zero, positive-negative sequence impedances Z0, Z1, Z2, is only exact if the system is symmetric since the application of voltage phasors of a sequence causes the circulation of current phasors only of the same sequence so that it is possible to compute the ratios between voltage and current phasors. The paper presents three meaningful examples of sequence theory use limitations
A Novel AC/DC Power Flow: HVDC-LCC/VSC Inclusion Into the PFPD Bus Admittance Matrix
Full text linkIn this paper, the matrix algorithm PFPD is generalized in order to compute the power flow solution of real and large AC/DC transmission networks. In particular, it is demonstrated that the HVDC-VSC/LCC links can be seen from the AC power systems as PV/PQ constraints, which englobe both the AC and DC characteristics of the HVDC links. The proposed analytical formulation to assess the PV/PQ constraints is valid for any other numerical methods (e.g., Newton-Raphson and derived, Gauss-Seidel, etc.). Furthermore, an iterative procedure for estimating the reactive power absorption of HVDC-LCC links from the power system is proposed. In order to validate the algorithm, solution comparisons with the commercial software DIgSILENT PowerFactoy are presented. This validation procedure shows that the algorithm can analyse large and real HVAC/HVDC networks (e.g., the Italian transmission one with its five HVDC links). Therefore, the conciseness, accuracy and performances of PFPD for studying real and large AC/DC power systems is confirmed
The Ossanna's Theorem for the Analytical Determination of a Two-Bus System PV Curve and Voltage Collapse Point
No full textIn the technical literature, the PV curves of the electrical lines are generally computed by only considering their electrical parameters as lumped. This model approach allows finding PV curve formulations without a large computational burden. Notwithstanding, such approximations bring to large inaccuracies for long transmission lines (especially insulated cables), for distribution ones (high r/x ratios) and for low power factor supply conditions. Starting from the Ossanna's theorem, novel and original PV curve and the voltage collapse point formulations for any electrical line are obtained. Moreover, PV curve analytical formulation considering the generator reactive power limits is formulated. Eventually, numerical results on the real-world case studies illustrate the differences with the proposed formulation with the classical ones found in the technical literature
PFPD-MCA: A Multiconductor Power Flow
Full text linkIn this paper, the multiconductor extension of the previously developed three-phase power flow algorithm (named PFPD-3P) is presented. This multiconductor formulation has a general validity for both distribution and transmission networks. An iterative matrix formulation for the solution is throughout expounded. The present method allows computing the electrical quantities of all the network conductors: the active conductors and the passive ones (i. e., OHL ground wires, IC metallic screens/armours, and GIL enclosures). These electrical quantities can be evaluated both at the network busbars and also along the lines. The knowledge of these quantities can be useful to perform: safety evaluations, power quality and electromagnetic compatibility studies. The electrical substations are carefully modelled, by considering the links between the passive conductors of different busbars and the earthing resistance of the meshed earth electrode. The algorithm is implemented in Matlab environment and tested by several fictitious networks. Eventually, in order to confirm the approach accuracy, the multiconductor results are compared with the equivalent single-phase ones and the three-phase power flow commercial software DIgSILENT PowerFactory
A Three-Phase Power Flow Algorithm for Transmission Networks: A Hybrid Phase/Sequence Approach
Full text linkIn this paper, the three-phase generalization of a single-phase power flow (named PFPD) developed by the first author is presented. This three-phase formulation is chiefly conceived for HV/EHV transmission network applications, but it preserves a general validity for any power system. An iterative method for the solution achievement is throughout expounded. The algorithm quantitatively aims at investigating the impact of the asymmetrical transmission structures on power systems. This impact is evaluated in terms of voltage and current sequence components. Moreover, discussions on possible improvement actions to enhance the power quality are developed. The algorithm is implemented in Matlab environment and tested by several fictitious networks. Eventually, extensive comparisons in terms of execution time, number of iterations and solution accuracy with the software DIgSILENT PowerFactory are presented
A New Algorithm for Multi-Area Power Flow
Full text linkIn this paper, a new algorithm computing the multi-area power flow problem is presented. This algorithm is suitable for AC synchronous areas operating in steady-state conditions and interconnected by means of AC tie-lines. In particular, a new iterative composition/decomposition matrix procedure is adopted. For each area, the classical PV, PQ, and slack bus constraints are defined, allowing the computation of the power flow of each area independently. This independency of the power flow solution of each area allows exploiting the parallel computation technique. The overall power flow is then computed by putting together all the solutions of each area iteratively, by means of the tie-line (i.e., the lines interconnecting the areas) admittance matrix. The present multi-area method is novel and completely general and once the power flow solution of each area is separately achieved by any power flow solver (e.g., Newton-Raphson and derived, PFPD, or other), it makes suitable use of both a Thevenin's theorem generalization and a novel tie-line admittance matrix. In this direction, the method is not a new power flow algorithm but a new multi-area algorithm, which starts from the solutions of the power flow of each area, each considered with its own slack-bus. Applications of the algorithm to standard test cases are presented. Eventually, to test the validity of the method, numerical comparisons with the commercial software DIgSILENT PowerFactory are performed
The Ossanna's theorem for educational purposes: Impact of distributed parameter transmission lines on power systems
Full text linkThis paper faces a challenge in power education: how to teach the students the impact of different transmission lines on the power system at power frequency. More specifically, the paper exploits the very effective and elegant Ossanna's theorem in order to make clear which are the allowable electrical regimes of different transmission line typologies in terms of power losses, voltage drops, transmissible powers and the conditions for the voltage collapse. Moreover, the formulation of the complex power at the sending-end of the power transmission line inferred from the Ossanna's theorem, which has never been shown in technical literature, is clearly presented. It is worth noting that although the paper is focused on high and extra-high voltage transmission lines, the presented didactical approach can be indifferently applied to any voltage level
Analytical formulation for estimating power low frequency oscillations between two overhead lines operating at different frequencies
Full text linkThis paper derives an analytical formulation to estimate the period and the amplitude of power low frequency oscillations originated by the mutual coupling of two power systems operating at two slightly different frequencies. This is the typical case of the power system restoration tests, in which the restoration backbone involves two overhead lines installed on the same tower. These oscillations have been detected during several real-world power system restoration tests with a non-negligible amplitude. In some cases, the active power exchanged between the two systems could damage the control and protection equipment of the elements involved in the test, leading to the failure of the restoration test itself. For these reasons, the analytical prediction of the period and the magnitude of these oscillations could constitute a useful and reliable tool for the planning and the simulation of the restoration tests
Design and modeling of an integrated flywheel magnetic suspension for kinetic energy storage systems
Full text linkThe paper presents a novel configuration of an axial hybrid magnetic bearing (AHMB) for the suspension of steel flywheels applied in power-intensive energy storage systems. The combination of a permanent magnet (PM) with excited coil enables one to reduce the power consumption, to limit the system volume, and to apply an effective control in the presence of several types of disturbances. The electromagnetic design of the AHMB parts is carried out by parametric finite element analyses with the purpose to optimize the force performances as well as the winding inductance affecting the electrical supply rating and control capability. Such investigation considers both the temperature dependence of the PM properties and the magnetic saturation effects. The electrical parameters and the force characteristics are then implemented in a control scheme, reproducing the electromechanical behavior of the AHMB-flywheel system. The parameter tuning of the controllers is executed by a Matlab/Simulink code, examining the instantaneous profiles of both the air-gap length and the winding ampere-turns. The results of different dynamic tests are presented, evidencing the smooth air-gap changes and the optimized coil utilization, which are desirable features for a safe and efficient flywheel energy storage
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