Thesis Defence of Mr. Rupam Pal @ 11am

Degree Registered; PhD

Guide: Prof. Udaya Kumar

Thesis Title: Influence of soil’s electrical parameters on lightning stroke-current evolution and fields in the close range

Date: 3^rd August 2022;  Time: 11.00 AM

Mode: It will be in hybrid mode. To join online: Click here to join the meeting

Venue:  MMCR Room, department of electrical engineering.

Abstract: The lightning return stroke forms one of the severest natural sources of electromagnetic interference for systems, both in the air and soil. Several physical fields govern this complex physical phenomenon, and most of the engineering applications resort to much simplifications. Several pertinent aspects are somewhat unclear, and it is not practical to conduct the field measurements to answer them. One such important aspect, which is of practical relevance, is the influence of soil’s electrical properties on the stroke current evolution and the fields in the close range. It is investigated in the present work.

Among different models for the lightning return stroke, only the ‘Self-consistent return stroke’ model is found to be suitable for the intended work. This model employs a macroscopic electrical representation of the underlying physical phenomenon to emulate the stroke current evolution.  However, this model has considered only a perfectly conducting earth and relied on the time-domain thin-wire formulation to solve for the associated dynamic electromagnetic fields.  On the other hand, a more realistic representation of the soil, including its dispersive nature and non-linearity, is required for the present work.  This necessitated suitable adoption of the ‘Finite difference time domain’ (FDTD) method for modeling the channel and its corona sheath, soil-ionization, and soil-dispersion.

The developed FDTD formulation is used to investigate and ascertain the role of soil’s electrical properties on the stroke current evolution and the field in the soil. For the first time, it is shown that the soil’s electrical conductivity has some noticeable influence on the stroke current magnitude, and the ionization phenomenon in soil tends to reduce this influence. The dispersive nature of the soil’s conductivity, and permittivity to a lesser extent, significantly reduces the field in the soil. The current concentration near the surface, which is expected for the skin-effect phenomenon, is altered at later periods by the field produced by the channel current. Also, the normal field in the soil changes its polarity. The vertical stratification of the soil, which is expected near the water body-soil interface, influences the field in the soil quite significantly. A strike to a model mountain leads to an entirely different field structure beyond its base. Similarly, a strike to a tall tower produces a field in the soil, which is bipolar near the tower base.  These are quite novel findings, and many of them are somewhat unexpected.

In summary, significant contributions have been made towards the FDTD formulations for modeling lightning phenomena and finding the role of soil’s electrical parameters on lightning stroke current evolution and the resulting field.