SWITCHING TRANSIENTS ANALYSIS IN THE PLANNING STAGE OF THE JAVA-BALI CONNECTION (JBC) HYBRID OHL-SUBMARINE CABLE 500 KV TRANSMISSION SYSTEM

• Main Author: P Nababan, Binhot
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/82190
• Institution: Institut Teknologi Bandung

The Java-Bali Connection (JBC) project, which employs the hybrid technology of an extra-high voltage (EHV) 500 kV overhead line (OHL) and cable with XLPE insulation, is a solution for meeting the growing electricity consumption in Bali by utilizing low-cost electricity from Java. This project is expected to be the first in Indonesia to use a 500 kV XLPE submarine cable. In power systems, switching operations are very common. Switching is needed for reasons such as isolation of grid components, transferring electrical energy from one circuit to another, isolating fault sections, etc. The switching process generates transients. In EHV systems, transient overvoltages due to switching are more critical than those caused by lightning. Transients are described in terms of electromagnetic fields and traveling waves. Due to structural differences, hybrid OHL-submarine cable systems will experience complex transmission and reflection of electromagnetic waves, particularly at discontinuities, leading to overvoltages that reach maximum values at the receiving end. This study focuses on analyzing switching transients in the upcoming JBC project, a hybrid of OHL and submarine cable, using DIgSILENT PowerFactory software based on a realistic power system model. Distributed-parameter models with constant parameters of the Bergeron model are utilized. Analysis of the traveling wave effect at line discontinuities is conducted, and the integration time step based on the time of the traveling wave is carefully selected. The contribution of this study is primarily directed towards the phenomena associated with transient operations during no-load energization and de-energization of mixed OHLsubmarine cable systems. It is observed that energization can induce overvoltages of very high values, which are identified as significant stresses on the insulation of system components. It has been strongly recommended by IEC standards that an insulation coordination study be conducted based on statistical simulations. The statistical distributions of energization, which assess the mechanical performance of the circuit breaker (CB) closure according to actual PLN specifications, are produced by varying the circuit configuration and the system's short-circuit level. The analysis incorporates 400 simulations. The switching withstand voltage (SWV) remains below the specified 1175 kV during the energization process, in accordance with the grid code. Moreover, it is concluded that transient energization overvoltages are likely to be ii higher when there is an increase in the network's short-circuit power. The probability distribution is fitted to a normal distribution, with the skewness and kurtosis shown to be skewed to the right and having a lower peak than that of the normal distribution, respectively. In lines equipped with two circuits and a shunt reactor (SR) connected to the line, parallel resonance problems can be encountered, particularly when one circuit is already energized and the other is to be energized. It has been determined in this study that parallel resonance will not occur in the JBC case when the SR is energized, because that the degree of SR compensation is only at 49%. When the SR stays connected to the line as a hybrid OHL-submarine cable circuit is turned off, the disconnected line exhibit decaying oscillatory AC voltages with superimposed frequencies. The increase in the probability of a CB restrike is caused by higher transient recovery voltages (TRV), which lead to the breakdown of the dielectric material in the CB. RRRV and TRV peak characterize the TRV. TRV due to a fault is more severe than that due to normal switching. Simulations show that when a three-phase short-circuit at the line breaker is induced, the RRRV exceeds the IEC standard envelope if only one circuit is operating. Adding capacitance will reduce the steepness of the RRRV but will result in an increased first peak voltage. The addition of capacitance decreases damping, which causes the amplitude of the voltage to rise and the voltage to become more oscillatory. Stochastic simulations and sensitivity analyses of various parameters related to the transient energizing and de-energizing of OHL-submarine cables have been identified in this thesis. This study is expected to become a reference that can be utilized in PLN system planning for evaluating the general feasibility of hybrid OHL-cable projects.