Analysis of Induced Sheath Voltages and Currents of 230 kV Oil-Filled and XLPE Underground Power Cables in The Tunnel: Case Study of Metropolitan Electricity Authority of Thailand

摘要

The sheath voltage and current in cover sheath of underground power cable are undesirable. The voltage can harm a worker who maintains the power cables by electric shock. Its value must not exceed standard and regulation for induced sheath voltage. Although the current is not directly affected to the worker safety, it affects to the system operation and efficiency. It generates heat losses and reduces the cable ampacity. So, it is very important to predict the sheath voltage and the current also. Elaborate analysis is required because it depends on various parameters. For instants, sheath bonding technique, cable geometry, insulation thickness, etc. In this paper, the voltages and currents induced in sheath for different installation of underground power cables (trefoil and flat formation) are studied and presented. Case studies are made on 230 kV oil-filled and Cross-Linked Polyethylene (XLPE) underground cables, which were installed in the tunnel of Lardprao-Vibhavadi project. Five types of bonding technique according to the utility's practices including case 1: single point bonding, case 2: mid-point bonding, case 3: double point (both ends) bonding, case 4: cross bonding non-transposed cables and case 5: cross bonding with transposed cables. For each case study of installation, the results of sheath voltages and currents have been compared. The results could be served as a guideline in transmission line design and improvement in the utility's power system.