Tips & News - January 2012


PROTECTA*LITE ARRESTERS A Radical Improvement in MAIFI with


When it was formed, Georgia Transmission Corporation (Tucker, GA) had a company-wide Momentary Average Interruption Frequency Index (MAIFI) of two. And, there was one transmission line with a MAIFI of ten. Today, the company-wide index is .92 and momentary outages on that particular line have dropped to less than one per year. Here is how GTC made those improvements.

Primarily due to Lightning

1997 2009

Company wide:



Worst Line



together, they account for about half of the US electric grid. For sustained outages, GTC is on par with the national average: Unfortunately, due to lightning, it ranks near the bottom of the list for momentary outage performance. To keep track of the lightning problem, in 2001, GTC started subscribing to the Viasala (Tuscon, AZ) lightning data service. Viasala sends information to GTC on all the lightning strikes in the state of Georgia. This includes the GPS location and magnitude of the strike, polarity, the date, the time (down to the millisecond). If a momentary outage occurs, the company takes the time stamp from the digital fault recorder (also in milliseconds) at the fault’s inception, and compares it to the lightning data. “If the fault inception was within 10 milliseconds of the lightning flash and if the GPS coordinates of the lightning strike are within a one kilometer buffer around the transmission line, then we are 95% sure that momentary outage was due to lightning. In a given year, anywhere

“Since its incorporation in 1997, one of GTC’s corporate goals has been to improve the traditional IEEE metrics, including MAIFI. Engineers began by determining what was causing the momentary outages and lightning was a major problem,” says Doug Maddox, Manager- System Reliability. Lightning Central This is not surprising, since after Florida, Georgia has some of the highest lightning densities in the United States. Parts of GTC’s area are close to the Gulf Coast and other areas are close to the Atlantic Ocean. Weather fronts come through year round with lightning occurring in every month of the year. The most vicious storms happen in the summer time--afternoon thunderstorms with the high magnitude lightning and heavy downpours. These storms have consequences. GTC sends its outage data to a consultant for benchmarking. About 30 other utilities are also part of the benchmarking program and,


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