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Unmodified steel poles can be lethal...

Excerpt from "Case Studies" section...

Case Study 3. The following is a summary of a paper presented at the 1998 IEEE Rural Electric Power Conference (IEEE Catalog No. 98CH36188) by Richard E. Harness, M.S. of Engineering Data Management, Inc. Keywords: Steel poles, Distribution, raptors.

Summary - Steel Distribution Poles - Environmental Implications. Because of certain advantages over wood poles, steel poles are becoming increasingly popular in distribution line construction. However, construction in the traditional manner typically results in reduced phase to ground clearances. These reduced clearances are particularly lethal to raptors. Since raptors are protected by state and federal laws, the burden for preventing electrocutions is placed upon the utility.

Details - Steel poles have certain environmental advantages over traditional wood poles. These advantages include a high strength to weight ratio, resistance to insect, animal, and bird damage, and the fact that steel poles do not require treatment with chemical preservatives. Lastly, steel poles are recyclable. Despite these advantages, steel poles can be extremely lethal to raptors (Birds of prey).

Raptors are often at risk when perched on grounded pole tops, particularly under wet conditions. A golden eagle's tail can extend 10 inches below its perch and wet feathers will sustain an arc at 5 kV. A large raptor with wet feathers can be electrocuted while perching on a center phase pin if its tail feathers contact a steel pole.

Wood has been used as insulation between primary current and ground, with a wood impulse flashover value of approximately 80 kV per foot. The use of wood typically results in a rating in excess of 350 kV BIL between primary conductors mounted on wood pole tops and crossarms, excluding equipment. The Rural Utilities Service (RUS) advocates a minimum of 300 kV BIL on steel tangent poles and deadend steel structures to minimize flashover. To reach the required BIL, insulators must be added to deadends and pole top brackets must be installed to provide additional insulation and air gap. One solution currently employed to increase the center phase separation from the top of the steel pole is the use of a pole top pin mounted on a pultruded solid fiberglass rod. Although the increased distance eliminates the possibility of electrocutions to birds perching on the pin insulator, the modification makes it possible for a raptor to perch directly below the phase wire on the grounded pole top. This new condition can be lethal to birds sufficiently large to bridge the gap between the steel pole top and center phase wire. Therefore, steel structures using extended pole top pins need additional modification to keep large birds off the pole top or away from the center phase.

A typical RUS three-phase C1 pole constructed with 10-foot crossarms provides the 60 inches of clearance recommended by the Raptor Research Foundation. However, when a steel pole is substituted, the phase to ground separation is reduced to 53 inches or less. If all the conductors are supported on a single crossarm, the horizontal clearances can be further reduced to 15 inches, clearly placing small and large birds at risk. The reduced phase to ground clearances on steel poles can be mitigated by wrapping the pole with a band of 40-mil thermoplastic polymer membrane with a pressure sensitive adhesive back. The required clearances can also be obtained by snapping insulating Kaddas Bird Guards over problem phase wires and insulators. Perch guards can be mounted on nonconducting wood or fiberglass crossarms to keep birds away from the pole. Steel crossarms on steel poles should never be used in areas where birds of prey exist.

An alternative to constructing lines in a traditional manner is to frame them in a form that allows safe perching. This can be accomplished by suspending two of the energized conductors under the crossarm instead of supporting them on the crossarm. Suspending the conductors allows birds to perch safely on the crossarm although poletop caps must still be employed to discourage perching on the top of the pole.

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