There is a significant opportunity to better understand, and eventual improve, the performance of transmission (TX) and distribution (DX) systems in response to direct and indirect lightning strikes using equipment and data currently available to the industry. To date, the operational analysis of lightning’s impact on power systems (lines) has been limited to information about basic lightning correlation and statistics, generally limited to the occurrence of faults.
Commercially available instrumentation and data are now poised to improve on this limitation. Broadband conducted current transients can now be measured with good fidelity and precise timing within substations and along any long cable on the system using modern digital relays, PMUs, or traveling-wave (TWS) fault locators. Waveforms associated with these transients can be stored and recovered for later use. Additionally, the precise paths of the lines are accurately known and are available in geographical analysis systems. Finally, we now have high-quality lightning “information” from ground-based lightning-locating systems (LLS) with both real-time and historical access. The occurrence of cloud-to-ground (CG) return strokes can be reported with a temporal accuracy of ~250 ns RMS and a spatial accuracy of 100-200m, at least in southern Canada and the United States. Additionally, these LLS systems can now record and forward waveform information about the radiated electric and/or magnetic fields produced by each stroke.
These observations can be used in concert to (1) improve the geolocation of faults on TX or DX lines, and (2) provide detailed information about both fault-events and non-fault transients. The geolocation of faults can be accomplished with as little as one conducted transient measurement in a substation or along the line, knowledge of the line path, and knowledge of the time and location of occurrence of the CG stroke, even if the stroke did not attach to the line (induced effects). This can be accomplished on lines with simple or complex interconnections. This analysis concept goes beyond the traditional assessment of “did lightning cause the fault.”
The concept introduced above should provide a number of benefits to the industry. When used as part of permanent infrastructure or as a temporary installation to understand a problematic line, the basic anticipated benefits are:
- Ability to identify the number of lightning strikes to the components of a line, and the associated peak current, irrespective of the occurrence of a fault. This should provide 10-20x more cases for understanding the ”lightning reliability” of a line, as compared to just analyzing faults.
- Ability to determine if a lightning-caused transient on a phase conductor (with or without a fault) was produced by lightning attachment to that conductor, the shield wire (or tower), or lightning striking the ground nearby.
- Possibility to determine if a lightning caused transient was in proper proportion to the lightning current (and possibly wave shape), reflecting local grounding impedance.
- For cases including faults, one should be able to tell if it occurred at the lightning strike location or if the transient voltage traveled a long distance before finding a location where breakdown occurred.
The objective of this “first phase” is to carry out further validation and demonstration of the concepts. This will be accomplished by a modest number of case studies through collaboration among the PI, participating utilities, and CEATI.