In the fall of 2004 AIR2 was approached by Georgia Power Co. to perform a specialized inspection on their 500-kV system to determine if there was a widespread problem with cracks that had been found in the bells of the insulators. The inspection quickly localized the problem to their 500-kV double dead end structures. The high power images from the inspection revealed hairline cracks that radiated out from the centers of the bells. Based on this inspection Georgia Power removed samples of these insulators and had them tested for structural and electrical strength.
The testing concluded that the cracked bells did not decrease structural strength. However, their insulating value was compromised. The insulators with cracked bells showed particular signs of electrical failure if there was a flashover incident. Georgia Power had already documented an insulator string exploding and attributed it to this problem. The inspection also concluded that the problem was localized to a particular insulator bell manufacturer, made in a single year. Georgia Power then decided to have all the structures that used those insulators changed as soon as possible.
The next problem was obtaining an outage on the critical 500-kV system. Because of the amount of work involved and the loading demand of the Georgia Power 500-kV system, it seemed impossible to get the work completed.
AIR2, LLC, a highly experienced helicopter transmission line construction and maintenance contractor, proposed performing the work under energized conditions. AIR2 had previously completed a hot insulator change on 230-kV I-string insulators for another utility. This work took place in early 2005 and was successful.
Georgia Power engineering and safety personnel and AIR2 personnel performed a thorough review of the procedures. AIR2’s hotstick/barehand trained line and flight crews then demonstrated their ability to safely perform this operation to Georgia Power personnel on the 500-kV system while deenergized. After these reviews and the demonstration, Georgia Power gave the project the green light. The photo shows the work in progress. The men have been transported to the structure and are on the structure using hot stick methods to install new insulators. The helicopter is departing with an old insulator on the end of a long line connected to the helicopter belly hook.
This work was performed in the 4th quarter of 2006 and 1st quarter of 2007 and was highly successful. This method offers a solution to many utilities faced with the same or similar problems with faulty insulators and difficulties obtaining outages.