In the modern power system, Flexible Alternating Current Transmission System (FACTS) devices are widely used. An increased share of the distributed generation (DG) and the development of microgrids change the power flows in the existing distribution networks as well as a conventional power flow direction from the transmission to the distribution network level which may affect the overall stability aspects. The paper shows the FACTS devices’ implementation influence on the performance of the distribution network with integrated renewable energy sources (RES) observing the aspects of the oscillatory stability and the low-voltage motor starting. The FACTS devices, in particular the static var compensators (SVC), have been allocated according to a novel algorithm proposed in the paper. The algorithm uses an iterative process to determine an optimal location for implementation and rating power of SVC considering active power losses minimization, improvement of the voltage profile and maximizing return of investment (ROI) of FACTS devices. Novel constraints—transformer station construction constraint, SVC industrial nominal power value constraint and the constraint of distribution system operator (DSO) economic willingness to investment in the distribution network development are considered in the proposed algorithm. The analysis has been performed on 20 kV rural distribution network model in DIgSILENT PowerFactory software.
In electric power systems, grid elements are often subjected to very complex and demanding disturbances or dangerous operating conditions. Determining initial fault or cause of those states is a difficult task. When fault occurs, often it is an imperative to disconnect affected grid element from the grid. This paper contains an overview of possibilities for using fuzzy logic in an assessment of primary faults in the transmission grid. The tool for this task is SCADA system, which is based on information of currents, voltages, events of protection devices and status of circuit breakers in the grid. The function model described with the membership function and fuzzy logic systems will be presented in the paper. For input data, diagnostics system uses information of protection devices tripping, states of circuit breakers and measurements of currents and voltages before and after faults.K e y w o r d s: fuzzy logic, primary faults, transmission grid Nomenclature |∆I| -absolute value of current change sensitivity I t -current after the event
Circuit breakers (CBs) in the transmission network are the basic elements for energy flow control. CB diagnosis represents a decisive action for increasing power system reliability and safety. Their actual availability status and ability to perform major functions can sometimes be difficult to determine. This paper presents a general state estimation model based on fuzzy logic (FL), membership function (MF), and expert knowledge for diagnosis schemes to handle unclear information in the diagnosis procedure. The proposed model uses inputs from the Supervisory Control and Data Acquisition (SCADA) system, data on the position and state of the switch, changes in current in the network element CB (NECB), start or trip action of a protection relay on the NECB, and alarm status of the CB. For the diagnostic system input variables, data from the SCADA system, along with transformer and line protection devices, are used to allow the proper formation of rules and ultimately to determine the diagnostic status of the CB. The proposed method is tested on an authentic test power system, and the outcome results are compared with a previously reported technique. The obtained test results and the comparison prove the efficiency, authenticity, and fast operation feature of the suggested strategy.
Electric and gas systems are two complementary, interconnected energy systems. Each of the systems has a different size and coverage. Their networks cover different areas, the structure of their customers varies across regions, and their presence varies in industry and households. The interrelatedness of these systems is both direct and indirect. The direct interrelatedness is visible in the tasks performed by the gas system in its function of a supplier for electricity production plants. Other than the mentioned direct connection, tasks performed by these two systems complement each other while supplying the consumers, for instance in tasks of heating, hot water preparation, and similar. However, there are also some specific features that create an impression that some systems' elements are separated. The indirect connection regards climate conditions. The aim of the paper is to analyse and present the impact which a temperature drop has on electric and gas system, as well as to analyse the interrelatedness of the two systems in extreme weather conditions taking Zagreb, Croatia as an example area. In winter the consumption of electrical energy and gas rises considerably. Any shortage leads to reactions. A threat to one system indirectly endangers the other. The paper tries to clearly present the systems' very important interrelatedness and interdependence in terms of higher demand for energygenerating products using the example of temperature drop. An immediate and considerable temperature drop provokes very similar responses from both systems. This phenomenon has not been recognized clearly enough by the professional community, and its consequences have not been fully considered.
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