AC interference effect of high voltage overhead transmission lines to nearby high voltage underground cables

• Main Author: Zoolnasri Bin Abu Harun, Mr.
• Format: text::Thesis
• Language: English
• Published: 2023
• Subjects: AC Interference Effect

Issues and interests of AC interference from Overhead Transmission Lines (OTL) to nearby objects or facilities has been studied by many researchers. It was found that the operation of OTL either during state or fault conditions has imposed a threat to nearby objects in its vicinity, especially those running in OTL Right of Way (ROW). This threat translates typically into an induced voltage or circulating current experienced by nearby objects due to electromagnetic interference from OTL energization. The common facilities usually within the OTL's ROW are gas pipelines, water pipelines, communication towers, and railways system, especially in populated congested areas. These interferences not only concern those mentioned facilities but also to another type of transmission system such as High Voltage (HV) underground cables that might share ROW with OTL. Due to limited land space and expensiveness of land acquisition to build new transmission networks, OTL ROW is utilized by having underground cables laid within the ROW. Nevertheless, the underground cable will also experience AC interferences from the OTL and study shall be conducted to assess the level of interferences before putting both systems in place. In this study, the objectives are to model, assess and analyze the effect of OTL to HV underground cables buried within OTL ROW by using Current Distribution, Electromagnetic Fields, Grounding and Soil Structure Analysis (CDEGS) software program. To evaluate the induced voltage, both systems are placed in vicinities where it comprises case studies of 132 kV, 275 kV and 500 kV OTL and 132 kV and 275 kV AC three-phase underground cables. The case studies cover different arrangements of both systems, such as length of parallelism, different energization values, crossing angle and varying soil resistivity. Modeling, simulation and analysis of interferences are presented to assess the induced voltage on the sheath of underground cables together with a proposed mitigation technique. This study investigates when OTL operates in steady state and fault conditions while the HV underground cable operates in normal conditions. The results show that the induced voltage on certain case studies increases above sheath standing voltage of 65 V. However, the induced voltage on cable sheath is reduced to tolerable sheath standing voltage by implementing mitigation techniques using underslung earth wires (underbuilt below phase conductors of OTL) and Ground Continuity Conductor (GCC) placed within underground cables. It is found that AC interference from OTL affect the induced voltage on cable sheath which can influence the performance of the underground cables. It is essential for engineers to simulate, assess and propose mitigation techniques to limit the sheath standing voltage of underground cable sharing ROW with OTL.