Imagine a Three-Phase Distribution Line, Radial Feed, Running West to East from town to town through cultivated fields. Also imagine the land being as flat as a pancake as far as the eye can see, with no wind breaks. Ameren (St. Louis, Missouri, U.S.) faced these exact circumstances.
In 2007, one of the Ameren Illinois divisions was looking for the solution to a problem it was having with high winds. The division had experienced wind-caused cascading wood-pole failures, at a rate of 8 to 10 poles at a time. The line in question is a radial feed into the town of Colfax, Illinois, U.S., an area known for high winds. It is probably just a coincidence that there is a wind-turbine facility just 5 miles (8 km) from the line.
The Ameren division had been evaluating this line and came up with an estimate of about US$180,000 to rebuild it. The division asked the Ameren Resource Management Group if there was a less-expensive alternative to strengthen or reinforce these poles to eliminate failures.
Ameren investigated several options including storm guying, higher-class wood poles, steel poles and pole reinforcement. The utility decided to try a new process know as the Pole Reclassification System (PRS) from Laminated Wood Systems Inc. (LWS; Seward, Nebraska, U.S.). The PRS enables utilities to reinforce wood poles with steel, providing the strength of a pole that is three or more classes heavier.
Ameren decided to use the PRS to reclassify poles in the line to eliminate the catastrophic span failures. The majority of the poles along the line were class 5 poles, 35 ft and 40 ft (11 m and 12 m), with spans from 250 ft to 300 ft (76 m to 91 m). Ameren contracted with Utilimap Corp. (Fenton, Missouri) to calculate the existing pole-loading condition of the poles and to install the PRS steel to the poles.
A pole-loading specialist walked the line to determine the type of construction, size of conductor and amount of equipment on the poles. The data was then given to Utilimap's engineering department, which calculated the mechanical loading of each pole. These results were then sent to LWS's engineering department, which ran further engineering analysis on the line and specified the steel units that would be installed to reclassify the poles.
The process to install the PRS involves the placement of two separate steel sections on the pole. The first unit of steel is driven into the ground next to the pole. Ameren used a Utilimap reinforcing crew to drive the steel. The second, or upper, unit is placed by an aerial crew. The upper unit is held in place temporarily with a ratchet strap while holes are drilled and cross-bolts are installed. The steel is cross-bolted to the pole, structurally connecting the units to the pole. For the Ameren project, once all the steel was installed, the reinforcing crew went back and put the high-strength stainless-steel banding on the poles to complete the installation procedure.
The project began on a Monday afternoon, and the last piece of steel was attached to the last pole on Thursday afternoon of that same week. Crews installed about 10 pieces a day.
Ameren gave the division two options and cost estimates to perform the reclassification. The first option was to reclassify all 48 poles that required reclassification, for around $80,000. The second option was to reclassify 27 poles, or every other pole, that required reclassification, for a cost of $40,000. The division chose the second option. By using the PRS process instead of replacing all the poles, the division saved approximately $120,000.
A week after the project was completed, a high-wind storm came through the area and tested the strength of the reclassification system. The division staff was concerned about how the line would hold up to the winds. The answer came via a phone call the following day. An individual who works in the division office and lives in Colfax called in to report that the line did not even have a blink, no outages or problems resulted from the high winds.
The second storm brought with it tornado-like winds that caused widespread damage within the division; but again, the PRS section of line held up. There was, however, another section of that line that was not marked for investigation and repair that had lost seven spans of line. The division will continue to monitor the success of the reclassification system on this line and plans to use this procedure as a new tool to repair other lines.
In addition to Ameren's reclassification project, the company is also using the pole-reinforcing process to save money. This program is used in both Illinois and Missouri. Poles that fail the company pole-inspections program are identified as reject poles during the routine line inspections.
The program identifies poles that are considered rejects in one of four categories. “P1 reject” is a pole that needs to be replaced quickly. “P2 reject” is a pole that needs to be replaced, but not as urgently as a P1 reject. “Restorable reject” is a pole that has decay in or on it, but the pole is still in good enough condition and the decay can be treated. Restorable reject poles are reinforced with one piece of PoleEnforcer steel. The last category, “Priority Restorable reject,” is a pole that usually has very little shell at the ground line but is solid aboveground. These poles are repaired using two pieces of PoleEnforcer steel, one on each side of the pole. Priority Restorable reject poles are often southern yellow pine poles.
Ameren's reinforcing program has achieved very large cost savings. Since 2005, the program has grown and continues to increase the number of poles being reinforced. A significant number of poles that would have been rejected in the past can now be reinforced using the double PoleEnforcer steel units. In 2007, the program did not reinforce as many poles as the previous two years, but anticipates reinforcing approximately 800 poles in 2008. Ameren estimates it has saved approximately $5 million in pole replacements by reinforcing these poles.
Jeffrey A. Gray, a construction supervisor for Ameren Corp., has been managing the pole-inspections program and the pole-reinforcing program for the state of Illinois since 2005. Prior to joining Ameren, Gray worked for Illinois Power as a field engineer rep in the engineering department, as an arm administrator in the Distribution Design Center responsible for the AMFM FRAMME system, as a distribution design specialist and finally as a compliance specialist. Gray received a bachelor's degree in industrial technology from Southern Illinois University - Carbondale in 1999 and is a member of the American Wood Protection Association.
|Year||Number of distribution poles||Number of subtransmission poles||Number of poles|
|Year||Cost to reinforce||Cost to replace*||Savings from reinforcing*|
|*Cost estimates based on the following assumptions: |
Estimated cost to replace subtransmission pole — $9100
Estimated cost to replace three-phase distribution pole — $5000
Estimated cost to replace pole in Missouri — $6000.
The estimated costs are based on an average between poles that have good access and poles that have difficult access to get to and change out.