Análise de estabilidade de tensão em casos de contingência simples de linhas de transmissão e compensação paralela

Abstract

The electrical system needs to be reliable and able to withstand contingencies to ensure power demand without overloading electrical equipment. In this research, the voltage stability of the STB-33 test system was analyzed in three situations: base case, after simulating simple transmission line contingency, and after applying shunt compensation in contingency cases with voltage violations. The ANAREDE software was used to simulate the contingencies and search for solutions using the Newton- Raphson method, discarding cases in which the removal of the line would cause isolation of grid elements, which resulted in 26 simulated contingency cases. Seven cases did not obtain an initial solution for the load flow, mainly in area A, which is not able to supply its demand alone, resulting in an energy exchange with area B. As a means of forcing the load flow solution, three methods were used: turning off the ANAREDE controls, representing the load at 75% active power and defining the bars interconnecting the contingent lines as reference. The last option resulted in the convergence of all cases and the lowest severity indices. The contingency cases with flow violations on the lines are mainly in area B, where area A imports power due to its demand being higher than supply. The cases with voltage violation in the busbars are mostly in area A, because the bars of this area are not able to support all its demand, resulting in voltage drops. For these cases, shunt compensation was applied, which is important to control reactive power in the grid and improve the performance of the transmission lines. Thus, FLUPOT was used to perform the optimal power flow calculations, determining the amount of reactive power to be allocated and the bars that should receive shunt compensation, proving effective in recovering the voltages of contingent and peripheral buses. Voltage stability studies identify vulnerable points in the system and a common method to determine these points is the PV curve, ascertained by the continuation method, using ANAREDE. Some bars did not remain voltage stable even after compensation, and were considered critical because they did not reach the point of maximum system loading. The base case had the highest loading and voltage safety margin, respecting the minimum limit pre-established by the National Electric System Operator (ONS), of 7% for complete systems. Cases 18 and 22, after the contingency, had the loading margin and voltage safety margin below the 4% limit, which is the minimum limit for incomplete systems. After compensation, these cases had an increase in the loading and voltage indices, respecting the criteria stipulated by ONS.