Impedance Method Used To Calculate Initial Switching Currents in Transmission Networks and Generator Real Power

Switching-on of transmission network elements can bring about high inrush currents in the network elements (lines and transformers) as well as sudden changes in real power of generating units. In order to reduce those disadvantageous effects in modern power systems switching operations are controlled by protection devices referred to as synchro-check. Optimal setting of the synchro-check parameters requires the application of adequate criteria and an efficient method for calculating current changes in lines and generators that result from switching operations. This article proposes a new calculation method based on a nodal impedance matrix. Such a matrix is commonly used for short-circuit analyses. The advantage of the proposed method is that a short-circuit software with an adequate extension can be also applied to the analysis of switching operations

Power System State Estimation Accuracy Enhancement Using Temperature Measurements of Overhead Line Conductors

Power system state estimation is a process of real-time online modeling of an electric power system. The estimation is performed with the application of a static model of the system and current measurements of electrical quantities that are encumbered with an error. Usually, a model of the estimated system is also encumbered with an uncertainty, especially power line resistances that depend on the temperature of conductors. At present, a considerable development of technologies for dynamic power line rating can be observed. Typically, devices for dynamic line rating are installed directly on the conductors and measure basic electric parameters such as the current and voltage as well as non-electric ones as the surface temperature of conductors, their expansion, stress or the conductor sag angle relative to the plumb line. The objective of this paper is to present a method for power system state estimation that uses temperature measurements of overhead line conductors as supplementary measurements that enhance the model quality and thereby the estimation accuracy. Power system state estimation is presented together with a method of using the temperature measurements of power line conductors for updating the static power system model in the state estimation process. The results obtained with that method have been analyzed based on the estimation calculations performed for an example system - with and without taking into account the conductor temperature measurements. The final part of the article includes conclusions and suggestions for the further research

Generation Level Matching to the Transmission Capability of Overhead Lines

The article presents a new algorithm for real-time current overload clearance in power lines. It combines an optimization method with a method of load flow tracing, which may seem a little futuristic, but it enables effective clearance of the effects of exceeded allowed transmission capability. The algorithm is meant for cyclical determination of such an allowed instantaneous value of generated power in each wind farm that makes possible to clear the overload having all the grid constraints satisfied

Optymalizacja doboru parametrów charakterystyk P(U) i Q(U) falowników mikroinstalacji fotowoltaicznych

Currently, a dynamic increase can be observed in the number of photovoltaic plants connected to a low voltage grid. The phenomenon of power flow towards a transformer substation may cause the permissible voltage to be exceeded. There are several ways to eliminate the adverse voltage increases. In this article, the authors proposed a method for optimizing the selection of P(U) and Q(U) characteristics of solar plant inverters. The research shows that the use of inverters, for which both characteristics have been activated, allows to master the problem of voltage increase with a small reduction of the micro-plant output.Obecnie można zaobserwować dynamiczny wzrost liczby instalacji fotowoltaicznych przyłączonych do sieci niskiego napięcia. Zjawisko przepływu mocy w kierunku stacji transformatorowej może spowodować przekroczenie dopuszczalnej wartości napięcia. Wyróżnić można kilka sposobów wyeliminowania niekorzystnych wzrostów napięcia. W artykule autorzy zaproponowali metodę optymalizacji doboru charakterystyk P(U) i Q(U) falowników instalacji fotowoltaicznych. Przeprowadzone badania wskazują, że zastosowanie falowników, dla których uaktywniono obydwie charakterystyki, pozwala na opanowanie problemu wzrostu napięć przy niewielkim ograniczeniu energii produkowanej w mikroinstalacjach

Elimination of Line Overloads in a Power System Saturated with Renewable Energy Sources

The increasing number of renewable energy sources (RESs) connected to power grids contributes to the emergence of not only balancing problems but also technical ones, such as the overloading of power lines. If renewable sources with a high generation level are planned to be connected in the area under consideration, then a large number of significant overloads should be expected, especially during contingency analysis. As a rule, high-voltage networks have a mesh topology, which is why the concept of using advanced mathematical algorithms was developed, with the help of which the resulting threats can be eliminated. This article presents a proposal for a new method of eliminating line overloads and determining the currently available nodal generation levels. Its innovation is a new method of eliminating problems related to the capacity of power grids. The high efficiency of the method results from the appropriately defined response of properly selected RES sources to the state of network congestion. The problem under consideration is illustrated with the example of a modified IEEE 118-bus test network. In order to eliminate line overloads, the article proposes a two-stage approach. In the first step, the sources that are most responsible for the occurring overloads are determined. In the second step, a metaheuristic algorithm is used to solve a nonlinear optimisation problem with constraints. This task involves reducing the power generated in the sources selected in the previous step in such a way that the resulting line overloads are eliminated, and, at the same time, the total value of the curtailed generation is minimal

Optimal Voltage Control in MV Network with Distributed Generation

The article presents the concept of voltage control in a medium-voltage network, using the classical control of a HV/MV (High Voltage/Medium Voltage) transformer and active participation of distributed generation sources. The proposed solution is based on the results of the optimization process. The objective function is considered as a single-criterion—the voltage quality indicator or value of power losses in the network, and optionally as two-criteria (voltage quality and losses combined, with appropriately selected weight factors). The analysis carried out for random selection of independent variables, using the original heuristic algorithm, indicated a very high efficiency of the proposed control process, compared to the traditional approach. A significant improvement in the voltage quality index and reduction of losses was found, which justifies the advisability of looking for new solutions in the field of voltage control in MV networks, taking into account active participation of distributed generation

Determination of Maximum Acceptable Standing Phase Angle across Open Circuit Breaker as an Optimisation Task

There are several threats that require the control of the conditions of switching operations in the transmission grid. They result mainly from the negative effects of the high-value current, which may appear after the breaker is closed. Problems considering closing the power circuit breakers on a large standing phase angle (SPA) are often formulated by grid operators. The literature most often discusses the problem of SPA reduction, which allows the system to be restored without the risk of damaging the turbogenerator shafts. This reduction can be achieved by various operational solutions; most often, it is the appropriate adjustment of active power generation, sometimes backed up by partial load shedding. The subject of the presented article is a slightly different approach to the SPA problem. The method of determining the maximum value of SPA for which the connection operation allows to avoid excessive transitional torques was presented. With this approach, finding the maximum value of SPA between the two considered system nodes is treated as an optimisation task. In order to solve it, the original heuristic optimisation method described in the article was applied

Determination of Maximum Acceptable Standing Phase Angle across Open Circuit Breaker as an Optimisation Task

There are several threats that require the control of the conditions of switching operations in the transmission grid. They result mainly from the negative effects of the high-value current, which may appear after the breaker is closed. Problems considering closing the power circuit breakers on a large standing phase angle (SPA) are often formulated by grid operators. The literature most often discusses the problem of SPA reduction, which allows the system to be restored without the risk of damaging the turbogenerator shafts. This reduction can be achieved by various operational solutions; most often, it is the appropriate adjustment of active power generation, sometimes backed up by partial load shedding. The subject of the presented article is a slightly different approach to the SPA problem. The method of determining the maximum value of SPA for which the connection operation allows to avoid excessive transitional torques was presented. With this approach, finding the maximum value of SPA between the two considered system nodes is treated as an optimisation task. In order to solve it, the original heuristic optimisation method described in the article was applied

Optimal Voltage Control in MV Network with Distributed Generation

The article presents the concept of voltage control in a medium-voltage network, using the classical control of a HV/MV (High Voltage/Medium Voltage) transformer and active participation of distributed generation sources. The proposed solution is based on the results of the optimization process. The objective function is considered as a single-criterion—the voltage quality indicator or value of power losses in the network, and optionally as two-criteria (voltage quality and losses combined, with appropriately selected weight factors). The analysis carried out for random selection of independent variables, using the original heuristic algorithm, indicated a very high efficiency of the proposed control process, compared to the traditional approach. A significant improvement in the voltage quality index and reduction of losses was found, which justifies the advisability of looking for new solutions in the field of voltage control in MV networks, taking into account active participation of distributed generation

Voltage Optimization in MV Network with Distributed Generation Using Power Consumption Control in Electrolysis Installations

Connecting a large number of distributed sources to the medium and low voltage grid poses many problems. The most important of these are the voltage changes inside the network, what can be observed when the power flow from these sources towards the HV/MV (High Voltage/Medium Voltage) transformer station. In particular, if the power consumption in nodes of the MV network is small and the distance between the place of installation of the source and the substation is large, increases and changes in voltage may be dangerous for the insulation of the network and burdensome for the consumers connected to it. The solution most frequently used to control voltage increases is the appropriate setting of the controller that affects the on-load tap changer of the MV/HV or even MV/LV (Medium Voltage/Low Voltage) transformer. It is also possible to regulate the reactive power of the sources and, of course, to limit their generated active power (curtailment of generation). The development of energy storage technology has made it possible to introduce consumers into the network, whose power can be controlled in a wide range. The article proposes the concept of an innovative voltage control system in the MV network, whose output values are three groups of parameters: HV/MV transformer ratio, reactive power of sources and active power of consumers connected in generation nodes. In the technological sense, it has been assumed that the loads are installations of electrolyzers used to produce “green hydrogen”, according to the P2G (Power to Gas) formula. The tests consisting in the execution of several hundred calculation cycles for the IEEE 37 test network, using the Monte Carlo simulation, have shown that the subordination of the hydrogen production process to the objectives of voltage control in the MV network clearly contributes to stabilizing its value, while meeting the technological requirements. The control variables of the proposed control system are the result of the optimization algorithm described in the article, the function of which is the quality of network voltage