Utilities to evaluate clearances following NERC directive

August 11, 2011

Electric power utilities and others who operate transmission lines will be paying close attention to locations where their lines pass over or near co-op distribution lines.

The North American Electric Reliability Corporation (NERC) recently issued a “NERC Alert” to Transmission Owners and Generator Owners stating that those who have not previously verified that facility design, installation, and field conditions are within design tolerances when the facilities are loaded at their rating, should describe plans to complete an assessment of their facilities to verify whether the actual field conditions conform to the entity’s design tolerances in accordance with their Facility Ratings Methodology. 

Basically, for Transmission Owners, this means that they must verify that their lines have clearances that meet current NERC Reliability Standards and National Electric Safety Code requirements.
 
“Duke Energy Indiana will be surveying the Joint Transmission System they own with Wabash Valley and IMPA,” said Brent Reyher, Manager, Delivery Services. “Because Duke is the operator of the transmission lines, they have the responsibility to pinpoint any potential clearance issues. For Duke, there’s a three-year timeline for compliance, and the highest impact facilities have to be done in 2011.  Duke has informed us that they’re initially focusing on the 345 and 230 kV lines this year and the 138 kV lines beginning next year.”
 
NERC’s action is an attempt to identify discrepancies between the clearances that were originally designed and today’s actual clearances. “NERC wants transmission operators to measure the space between conductors and any foliage, structures, as well as the space between their lines and those of other electric and telecom utilities,” Brent added. “They have to consider not only what the clearance is when they measure it, but also apply calculations to see if it would continue to comply at each line’s designed temperature.”
 
Because of the need for accuracy and the sheer scope of the job, many transmission operators are using LiDAR (light-detection and ranging) systems to measure clearances. Those systems use a helicopter or airplane in conjunction with GPS data to obtain very accurate information on those facilities being surveyed. An infrared laser in the helicopter or airplane sends thousands of pulses per second, and the speed of their return is measured by a sensor. When coupled to GPS data, the systems provide measurements that are accurate to less than a third of a foot.
 
So what happens if a clearance problem is detected? According to NERC and MISO, the affected transmission line may need to be removed from service until the clearance issue can be resolved. “A co-op might not be served by that line,” Brent stated, “but they may have a distribution line running under it, and that line may need to be shut down so the transmission line can be serviced. One concern is that shutting down a transmission line on a hot day could create problems for the overall system.” In addition to foliage and other lines, clearance issues could be caused by everything from structures to piles of junk cars.
 
“We believe that all of the transmission operators will be checking their lines soon, although it appears that Duke Energy is the only one that has started within our service territory,” Brent noted. “We’re asking our members to give Duke contact information for the co-op staffers who they can talk with if there is an issue. Since Wabash Valley is an owner of the Joint Transmission System, we hope everyone will cooperate in a timely, cost effective manner, because resolving any noncompliant lines is in everyone’s best interest.”
 
“NERC Alerts that are “Recommendations To Industry” are not mandatory,” explained Susan Sosbe, Compliance Manager. “However, in this case, NERC required transmission owners and generation owners to submit timelines of how they’re going to address the issue.  The NERC Alert is tied to Reliability Standard FAC-008.  NERC is telling transmission and generation owners that they need to perform the assessments using methods or technologies with adequate precision to show whether the actual field conditions support the entity’s facility ratings.”
 
Susan said that NERC is encouraging rapid responses. “They issued a Compliance Application Notice stating that remediation should be completed as quickly as practical, consistent with maintaining bulk power system reliability,” she added.