Importance of Transient Study in Transmission Lines
A coal-fired thermal power plant was connected to a national ring network through transmission lines. One of the transmission lines faced an insulation flashover during lightning. The flashover was rampant in this geographical location.
The insulation flashover resulted in an earth fault where the arc shorted the charged line to the transmission tower resulting in line shutdown. The outage of the 300MVA line can result in a revenue loss of approximately 134000 USD (1 Crore) per day for a generating station.
Perform transient study to find the insulation coordination of lightning arrester & efficacy of grounding systems installed at the substation of the generating station.
Lightning transient response analysis determines the reason for insulation flashover. Substation earth grid and tower footing details are necessary to simulate assigned electrical fault level to determine:
- Transient response
- Step & Touch Voltage
- Transfer Potentials
The response of electrical networks to lightning was studied using the Electro-Magnetic Transients Program (EMTP-RV). A lightning with a waveform 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 analyzed at transmission towers and susceptible locations in the substation.
Transient analysis performed helped to determine the following.
- Stress across the tower insulators which vulnerable at the time of lightning
- Surge impedance substation earth grid and tower footing.
- Backflash over of the insulator
- Efficacy of lightning arrestor
This analysis allows surgical correction of insulation & grounding systems by increasing the utilization efficiency of O&M assets.