Modeling of lightning strikes at overhead lines: A method to determine insulated cable joints protection

The direct impact of a lightning strike at electrical systems and living beings can lead to destruction of system elements, equipment and eventually death. The resulting magnitude of voltage and current can be attenuated or amplified, due to the reflection process of their waves in points of the system where there is discontinuity of the surge impedance value. The objective of this study is to present an incipient method for investigation of electrical transients due to lightning strikes that reaches directly on overhead lines with an underground insulated cable section. The influence of varying number and positioning of MO arresters in the system, also the variation of the underground cable length, on the maximum voltage at the insulated cable joints are evaluated. This voltage cannot exceed the safety margin considered for the Basic Insulation Level Margin (BIL) of the insulated cable. The energy absorbed by the MO arresters is also analyzed. The results are representative regarding the use of MO arresters to protect transmission lines with insulated cable sections. From the obtained total energy and safety margin, it can be determined which configuration and protection arrangement is the most technically viable.