Abstract
This study determines the voltage across insulators after a direct lightning strike to an overhead ground wire on a 24 kV pole structure for different grounding distances of overhead ground wire, to calculate the maximum ground resistance required to avoid disruption of the distribution line system using ATP-EMTP software. The results show that when a 40 kA lightning current, the average lightning current in Thailand, strikes a 24 kV pole structure, the maximum ground resistance should not exceed 4 Ω for a 40 m grounding distance of overhead ground wire, based on an existing critical insulator flashover of 205 kV. However, because the average ground resistance in Thailand is approximately 10 Ω, this study proposes increasing the insulation level from 205 kV to 300 kV to reduce the likelihood of power outage. The cost-effectiveness of such an investment is assessed in terms of net present value (NPV), internal rate of return (IRR), profitability index (PI), and discounted payback period (DPP) using existing economic tools. Results show that when the critical insulator flashover is increased from 205 kV to 300 kV for a 40 m grounding distance of overhead ground wire, the project is likely to have a DPP of 15.12 years, NPV of 143,321.87 USD, IRR of 12%, and PI of 1.15. On the other hand, grounding distances greater than 40 m for overhead ground wire result in negative NPV, although the back flashover rate can be reduced by 1.51–5.71% with grounding distances of 80–200 m compared to the situation in the absence of grounding.
Highlights
KV power distribution line networks in ailand are the most important infrastructures for sending electricity to customers. erefore, disruptions on these distribution lines will cause significant economic losses
Piantini [10] indicated that the flashovers of an insulator in a medium voltage system due to indirect lightning current are less frequent if the critical flashover (CFO) of the insulator is more than 300 kV and found that the lightning protection level will decrease when the grounding distance of overhead ground wires (OHGWs) is wider and the soil resistance is higher
On the other hand, when the grounding distance of OHGW is increased from 40 m to 200 m, the minimum critical impulse flashover is increased from 268 kV to 360 kV when the lightning current is 40 kA
Summary
KV power distribution line networks in ailand are the most important infrastructures for sending electricity to customers. erefore, disruptions on these distribution lines will cause significant economic losses. Piantini [10] indicated that the flashovers of an insulator in a medium voltage system due to indirect lightning current are less frequent if the critical flashover (CFO) of the insulator is more than 300 kV and found that the lightning protection level will decrease when the grounding distance of OHGW is wider and the soil resistance is higher. This study is based on the 40 kA average lightning current in ailand striking a 24 kV distribution system with an average ground resistance of 10 Ω For this setup, the insulation level should be increased from 205 kV to 300 kV for the system to be able to withstand a 40 kA lightning current.
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