Colloquium 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:                     9.30 AM, 12^th April 2024

Venue:                                   High Voltage Laboratory Seminar Hall of EE Department

Research Supervisor:           Professor 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, conductor snapping, etc. In many cases, through lightning, they cause several flashovers on the EHV/UHV grid. However, there is no serious effort to estimate the possible number of flashovers caused by the lightning produced by such cyclones. The present work aims to fill this serious gap.

The estimation of such lightning-induced flashovers requires several aspects, both electrical and cyclone-related. The lightning stroke 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 for assessing 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 relation between the peak stroke current and the rise time is made based on the literature. Then, by modelling the lines in EMTP with a multi-story model for the tower, simulations are carried out to deduce the corresponding voltage rise. Using this information and the BIL of the line, the possibility of flashovers is assessed.

The trajectory of the cyclone and the speed, along with the number of lightning flashes produced by them are assimilated from different sources. Modelling the cyclone as a disc above ground, 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 these information, the possible number of lighting-induced flashovers in the EHV/UHV grid along the east coast is estimated.  Within three to four days the number of such flashover incidents can range from a few to few tens of flashovers within a time span of two to four days.