Pole inspection and maintenance procedures vary greatly among utilities. Inspection proce- dures also differ for transmission and distribu- tion lines. There is no uniform standard or consistency in frequency or nature of inspec- tions or maintenance. Some utilities use third- party contractors, while others have no set process in place.
The types of inspections reported include ae- rial infrared, foot patrols, climbing and ground line inspections. Visual inspections are used to identify excessive lean, external damage, unauthorized foreign attachments, lack of foundation integrity and excessive corrosion. Frequency of inspections varies substantially. For example:
• Jackson Energy inspects on a two-year cycle.
• Kenergy is on a 10-year cycle.
• Big Sandy RECC inspects approxi- mately 10 percent of its poles annually.
• Taylor County RECC inspects all cir- cuits served by one substation each year.
• Fleming-Mason Energy uses an eight- year inspection cycle.
• EKPC inspects its transmission system poles initially at the 16-year point and at 12-year intervals thereafter.
• Duke Kentucky has three different types of inspection: 1) transmission lines are inspected every two years by a line pa- trol, helicopter survey and aerial inspec- tions; 2) distribution lines are visually inspected every two years; and 3) distri- bution lines are ground-line inspected every 12 years.
As with the type and frequency of inspec- tions, utilities also take varying approaches to the preservation of poles after installation:
• Outside contractors are used by some of the utilities ( i.e., Blue Grass Energy, Inter-County Energy, and Jackson Pur- chase Energy) to determine if pole treatment is necessary.
• South Kentucky RECC, Taylor County RECC, Salt River Electric, Jackson En- ergy, Cumberland Valley Electric, Farm- ers RECC, Grayson RECC, and Licking Valley RECC do not have pole treat- ment programs.
• Kentucky Power inspects and maintains its poles in accordance with AEP
(parent company) Specification 125
Company Broken Poles
Kentucky Power No Damage Reported BREC 24 Duke Kentucky No Damage Reported EKPC 3 KU 183 LG&E 5
Total 215
Table 4: Broken transmission system poles, by utility—2009 ice storm
“Specification for Inspection & Ground line Treatment of Standing Wood Poles,” which includes treatment with pesticide and preservatives with a ban- dage arrangement around the base of the pole.
Kenergy and EKPC use treatments that in- clude the application of supplemental paste preservative directly to the ground line area which is most susceptible of decay. Big Sandy RECC does boring, visual inspection, fumigation and ground line treatment. The main components of a pole installation include the pole foundation, the pole itself, conductors, guys and anchors. Some utilities stated that the weakest component of a pole installation varies by the predominant type of load (wind, ice, combined wind and ice, etc.) and resistance to unanticipated loads such as trees falling on lines and structures which ex- ceed design loads. Other utilities stated that the weakest component of any particular pole installation will be the component for which the applied loads most nearly reach its allow- able loads, which will vary depending on the application and the arrangement of the vari- ous components.
A number of utilities provided very similar as- sessments, with several noting that C.H. Guernsey & Company, an engineering con- sulting firm, had assisted in the preparation of the following response:
Each pole installation’s group of compo- nents are arranged and sized to work to- gether to support the applied loads. Often the strength capacity of one component will rely greatly on the use of other com- ponents for support. It is very situation specific, but failure of an individual com- ponent within a group can ultimately lead to complete failure of the structure and, furthermore, failure of complete sections of line. The measure of integrity that re- mains in a structure following the failure of one of its components will vary depending on the application and the arrangement of its components.
However, EKPC and Duke Kentucky both stated that the weakest component is the “pole itself.” Duke stated:
A typical distribution structure consists of pole, cross arm, cross arm braces, insula- tors and hardware to assemble the struc- ture. Loads applied to the structure in- clude transverse, vertical and longitudinal forces. During the design process, three- dimensional modeling software is used to evaluate the loads a structure would be subject to based on NESC requirements. This software will also display the per- centage that a structure is loaded by com- ponent. For a typical tangent structure, the greatest structure load is usually gen- erated by the transverse wind load when applied with ice loading. For transverse wind loading the limiting factor is usually the pole not the cross arm, cross arm braces or the insulators.
EKPC responded:
Failures that occur with transmission lines are normally the result of weather condi- tions- high wind events, ice storms, etc. LG&E pole snapped by the 2008 wind storm
These failures happen as a result of over- loads which have been concentrated at the points of support. The wires serve to transfer the loads to these support points. As an example, during heavy ice loading conditions the weight of the ice on the wire is transferred to the supporting struc- tures resulting in increased loads on those structures.
The wires rarely ever experience loadings that would cause them to fail (break) since they are normally designed for ten- sion of approximately 50% or less of the rated breaking strength. Also, wires have a certain amount of elasticity (stretch) be- fore failure. The insulators and hardware support only one wire and, thus are sub- jected to only the loads transferred by that one wire. However, the supporting struc- ture is subjected to the loads transferred from all the wires that are attached. Insulators and hardware are specified and designed such that they rarely ever fail
before the supporting structure. Some supporting structures may include crossarms or davit arms. In some cases these arms will fail prior to the poles fail- ing. Thus, poles and arms (if present) are normally the most critical components of a structure.
LG&E, KU, Big Sandy, BREC, Taylor County RECC, Fleming-Mason Energy, Shelby En- ergy and Nolin RECC all stated that their pole installations are not designed with planned failure points that minimize overall damage. These utilities pointed out that a multitude of different weather and environmental condi- tions can affect various components of a structure in different ways. Designing certain components to fail first could result in creating more outages due to the possibility of prema- ture release at times other than storm events and cause wires to break and/or sag low to the ground. This could present a serious haz- ard to the public that might not have other- wise existed.
Kenergy pole with multiple failure points during 2009 ice storm
The utilities were asked to identify other is- sues related to pole failures that may not typi- cally be considered during the design and inspection process. Most did not identify other such issues. Clark Energy, however, de- scribed several factors that may contribute to pole failures:
• Location of poles: some soils may not have the ability to hold poles in place properly when the pole is subjected to wind or other similar forces in a storm.
• Some of the routes used for pole place- ment are not ideal.
• Creeks, rivers, and other streams can cut into banks over time and during a severe weather event the poles can be “washed out.”
• Deterioration of pole tops may also be overlooked, but can break and cause outages.