Importance of Transient Study in Transmission Lines

T . E . C . T Tackling Electrical Concerns of Today

Written By : Mr. Sonjib Banerjee

Edited By : Dr. Diksha Rohra

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Problem Statement

A power transmission company having 171,950 circuit km (CKM) transmission lines and 262 sub-stations was facing insulation flashover during lightning. The flashover was rampant only in few geographical locations.

Consequences

The insulation flashover resulted in earth fault where the arc shorted the charged line to the transmission tower resulting in line shutdown. Outage of 300MVA line can result in a revenue loss of approximately 134000 USD (1 Crore) per day for transmission as well as consequential losses of loads fed by this transmission line.

Solution

Perform transient study to find the efficacy of insulation & grounding systems deployed.

Case Analysis

Lightning transient response analysis determines the reason of insulation flashover. Substation earth grid and tower footing details are necessary to simulate assigned electrical fault level to determine:

  1. Transient response
  2. Step & Touch Voltage
  3. Transfer Potentials

The response of electrical network to lightning was studied using Electro-Magnetic Transients Program (EMTP-RV). A lightning with a wave form and amplitude as per IEEE recommendations, was applied to observe the transient response of insulators and change in tower footing resistance. These transient responses were analysed at transmission towers and at susceptible location in the substation.

Benefits

Transient analysis performed helped to determine the following.

  1. Stress across the tower insulators which vulnerable at the time of lightning
  2. Surge impedance substation earth grid and tower footing.

This analysis allows surgical correction of insulation & grounding systems by increasing the utilization efficiency of O&M assets.

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