Thesis defense on Estimation of flashovers in the EHV/UHV lines on the east coast due to lightning produced by the Bay of Bengal cyclones

Name of the Candidate:  Anirban Chatterjee

Title of the Thesis:         Estimation of flashovers in the EHV/UHV lines on the east coast due to lightning produced by the Bay of Bengal cyclones

Degree Registered:         MTech (Res) in Electrical Engineering

Time and date:              11.00 AM, 10^th June 2024

Venue         :               MMCR Seminar Hall of EE Department

                                    Meeting Link

Research Supervisor:      Udaya Kumar

Abstract

The Bay of Bengal produces a considerable number of cyclones. Many of them invade the east coast of India. They can cause structural damage to towers, substation flooding, and conductor snapping. In many cases, lightning causes several flashovers on the EHV/UHV grid and they are much more in numbers than the former. However, no serious effort was made to estimate the possible number of flashovers caused by the lightning produced by such cyclones. The present work aims to fill this serious gap.

Estimating such lightning-induced flashovers requires several aspects, both electrical and cyclone-related. The lightning strike could be intercepted by the tower/ground wire, or it can strike the phase conductor. The electro-geometric model (EGM), suggested in IEEE standards, is employed to assess the normalized number of strokes striking the phase conductor and intercepted by the tower/ground wire. The associated probabilities are also estimated for typical EHV and UHV lines.

The simulations are carried out by modeling the lines in EMTP with a multi-story model for the tower and the voltage rise in the system is evaluated. Using this information and the BIL of the line, the possibility of flashovers is assessed.

The cyclone’s trajectory, the speed, and the number of lightning flashes produced by them are assimilated from different sources. Modeling the cyclone as a disc like structure,, the line length shadowed as a function of time is calculated. In addition, equivalent ground flash density per square km per hour is also calculated. Combining all this information, the possible number of lighting-induced flashovers in the EHV/UHV grid along the East Coast is estimated.  It amounts to 100s of flashover in 400 kV lines and 1000s of flashover in 220kV line.

For engineering purposes, the maximum number of possible flashovers are required. Based on the maximum number of ground flashes per hour across the cyclones for five years, it was estimated. It amounts to a few to a few tens of flashovers in 765kV grid, a few tens to a few hundred in 400kV grid and that for 220kV grid, it amounted to a few hundred to a few thousands.