Power Flow Analysis in N-1 Contingency Conditions Due to the Entry of Renewable Power Plants in the Sulselrabar System

— Contingency analysis on a 150 kV network aims to see the network's reliability against interference. Contingency is a scheme for releasing one element of the generating unit or transmission line (N-1), which will affect the performance and reliability of the electric power system. Power flow analysis in an electric power system is an analysis that reveals the performance of an electric power system and the flow for certain conditions when the system is working. The analysis was carried out using the ETAP 16.00 software. The method used was the newton raphson to calculate the load flow in the N-1 contingency condition. From the results of the study, it can be seen that the power flow occurs in each channel of the 150 kV system in the South Sulawesi system. When conducting a contingency analysis of N-1 by removing the load on the middle lane of South Sulawesi, namely Maros and Sidrap, a voltage change occurs, increasing buses experiencing critical and marginal voltage conditions. This happens because of the sudden release of essential loads, so over or under voltage appears on the bus.


I. Introduction
The electric power system is vital in providing and delivering electrical energy to the load reliably and continuously. The need for electrical energy continues to increase in direct proportion to the increase in the transportation sector, industry, and other activities that require electrical energy. To provide reliable service, the electric power system must be able to overcome various kinds of disturbances that may occur [1].
Disruption of the discharge of the generating unit or transmission line in the electric power system is unavoidable, so if the disturbance occurs, it can cause the flow of power to be channeled to experience a significant change. This term is closely related to the ability of a system to serve the load in the event of a disturbance in one of its elements.
Contingency analysis is the study of the safety of the electric power system by analyzing the power flow from the impact of several N-1 contingency cases (release of one generating unit or transmission line). With the contingency analysis of an electric power system, it is possible to calculate the disturbances that occur in the transmission line so that it can predict changes in transmission capacity and the remaining bus voltage, whether it can still be loaded or has experienced an overload condition. So it is essential that the system be planned so that in the event of a contingency condition of one of the transmission lines, it does not result in blackouts in part or all of the system [1].
After the presence of the Wind Power Plant, it can increase the stock of available power capacity in the South, Southeast, and West Sulawesi (Sulseltrabar) regions, thus increasing the number of burdens that must be borne. For this reason, it is necessary to conduct a power flow analysis to determine the overall condition of the electric power system in the current Sulselrabar system. Power flow analysis in an electric power system is an analysis that reveals the performance of an electric power system and power flow (real and reactive) for certain conditions when the system is working [2]. The main result of the power flow is the magnitude and phase angle of the voltage on each line (bus), the real power, and the reactive power on each line [3].
In this study, two methods of analysis were carried out: when the system was in average condition and contingency N-1. Under normal conditions, it will be known how much active power and reactive power occur, while in the N-1 contingency, it will be known the changes in dynamic power and reactive power that arises. The Performance Index (IP) was obtained from the calculation. The calculation of the power flow for the electric power system in the Sulselrabar System section after the entry of renewable plants, if done manually, will be very complicated and requires a lot of time, therefore in this study, computer software was used to simplify and speed up the process of calculating the power flow. ETAP (Electrical Transient Analysis Program) Power Station is software that can calculate the flow of power in an electric power system. Using the ETAP Power Station 16.00 software, you can analyze a comprehensive electric power system and many conditions [4].
Previously, some studies discussed average power flow analysis and the N-1 contingency condition. For moderate conditions, as in research [4] which discusses the analysis of power flow in the South Sulawesi system, [5] discusses the analysis of the power flow of the electric power system in the texturizing section at PT Asia Pacific Fibers Tbk Kendal, [6] discusses the voltage analysis of each bus in the Gorontalo electric power system through power flow simulation, [7] discusses the study of power flow in the South Sulawesi electrical system, [8] discusses the contingency analysis of the Riau electric power system using the Newton Raphson power flow method, [9] discusses the load flow analysis on the East Kalimantan interconnection system. As for N-1 contingency conditions, such as [1] discusses contingency analysis in the Central Java system, [10] discusses contingency analysis by calculating two active performance indices (PIP) and reactive power performance index (PIV) for single transmission line blackouts, [11] iscusses the contingency analysis of the power system using voltage and active power performance index, discusses the study when there is a blackout in each component or equipment in the power system, contingency analysis shows an indication about what might be the position of the power system [12] discusses the contingency analysis of the unbalance transmission system. From these studies, it is necessary to develop a power flow analysis, such as an up-to-date analysis, by testing several case studies. The current Sulselrabar system continues to grow [13], especially after the entry of several renewable plants and in the N-1 contingency condition. The power flow characteristics need to be reviewed to see the system's features. This study proposes a power flow analysis approach to enter renewable power plants in the Sulselrabar system under N-1 contingency conditions.

II. Research Method
The research was conducted by simulating the electric power system of the Sulserabar system of PT. PLN AP2B Sulselrabar Region due to the entry of renewable power plants using the ETAP 16.00 application. The modeling of the system to be carried out adjusts the parameters needed and has been accepted by the researcher when collecting data. The simulated system is designed in such a way as to achieve similarity to the actual 150 kV Sulserabar network system.
The initial step of the research is to determine the parameters or technical data supporting the desired value. This data will be obtained when researchers carry out data collection at PT. PLN AP2B Sulselrabar Region, Makassar.
After the data and method analysis has been carried out, the next step is to design a single-line diagram of the 150 kV Sulselrabar network system on the ETAP 16 application, which helps facilitate the next stage.
Network modeling is the next step by entering data in each installed component with already available data. The modeling stage plays an essential role in this research because the network is made according to the actual conditions of the Sulserabar system.
After the design and modeling are complete, the next step is to run load flow on the ETAP 16 application to ensure the modeling runs well. After successfully simulating, the power flow results are obtained, then identify the parameters of active power and bus voltage under normal conditions before the N-1 contingency scheme is carried out.
In the next step, the researchers simulated contingency by removing one channel installed in the selected system and conducting a power flow analysis during contingency. Then analyze the power flow generated during contingency by identifying the parameters needed for calculating the Performance Index. The active power and bus voltage will be recorded during line disconnection.

III. Results and Discussions
The currently active Sulselrabar electricity system consists of 21 generating units, namely 6

a) N-1 Contingency Power Flow Simulation Results After Wind Turbine Entry
The contingency simulation analysis of the 150 kV Sulselrabar interconnection system after the entry of the Wind Turbine is made to determine the voltage and current conditions when a load is released. This simulation releases the load on the middle lane of the Sulselrabar system, namely Maros and Sidrap. Then the following results are obtained.

b) Active Power and Reactive Power Simulation Results
After disconnecting the load from Maros and Sidrap, the simulation is carried out again as in normal conditions, resulting in data for active and reactive power, which flows in each channel in table 2.

c) Active Power and Reactive Power Interconnection
System 150 kV Sulselrabar Contingency N-1 The results of the N-1 contingency power flow simulation analysis can produce the following data conclusions,

d) Active Power and Reactive Power on Bus Loading
The simulation results using ETAP with the Newton-Raphson method show that the differences in active, reactive, and PF (Power Factor) occurs in each channel. The Loading bus's total active power (P) is 1077.21 MW. The Bus Loading with the most significant active power is found in the Loading BD_10 bus, which is 231.50 MW with a reactive power (Q) of 45 Mvar and a Power Factor of 98.16%, while the complete results can be seen in table 3 below.

e) Voltage Simulation Results at Each Bus When Contingency N-1 Sulselrabar System 150 kV
The voltage at each bus is 150 kV in the Sulselrabar system when the Maros and Sidrap load. At the same time, the voltage changes in the sulselrabar system as a whole can be seen in table 4, which can also be seen in Figures 1 and 2 of the respective voltage profiles buses.  Critical Voltage Condition is a condition where the voltage on the bus cannot be tolerated because it exceeds the standard PLN limit, while the Marginal Voltage Condition is when the bus is in a state of over-voltage but is still within the allowable limits. It can be seen in the graph that many buses experience over-voltage due to voltage drop due to the loss of large loads on Maros and Sidrap. Buses sharing Marginal Over Voltage can be seen in

IV. Conclusion
The conclusions obtained from the results of the analysis are that the Newton-Raphson method used for power flow simulation in this study shows efficiency in terms of the speed of the computational process in ETAP 16 Software. There are 2 impacts generated when the Maros and Sidrap loads suddenly release, namely 6 buses experiencing Critical Voltage Condition and 34 buses experiencing Marginal Voltage Condition, which is 34 buses.