By D. Thompson
Everyday we are faced with alternative products made of new and innovative materials. Materials, once considered "space age" fill our lives in the form of nylons, teflon, alloys and plastics. Often new products radically out-perform their predecessors and often for similar reasons. New materials tend to be more consistent, lighter, cheaper, last longer, and they can be more interchangeable, versatile, and easier to use.
Steel, as a construction material, surrounds us. It is found in structures that have stood for many decades and will be around for years to come. Yet when presented with the option of steel distribution poles, many utilities react with disbelief, skepticism.
The time is coming for utilities to consider steel for use as distribution poles, and to catch up with world wide perceptions about the use of the product.
Steel poles have a recognizable edge over wood poles in the area of environmental issues, manufacturing quality controls, strength to weight ratios, resistance to elements, handling and storage and one day may be the everyday pole of choice.
York Hydro is a medium-sized municipal utility in Metro Toronto. We have a staff of 97 and a customer base of 36,000. Our peak load of 168+ MW was set in January 1994.
At York Hydro we have undertaken a trial project to review steel poles as a possible new standard material. We rebuilt a street over the winter of 1995/1996 and used about 20 steel poles of various sizes. We have an on-going project to install about 70 more steel poles in a "live" situation and where steel poles are the only practical solution.
Our size makes us well suited to try products such as steel poles since we have the resources to investigate new ideas, yet our compact structure meant it only took 3 or 4 people to agree to the pilot.
Steel Poles
At York Hydro, the existing standard pole is wood and therefore most of the comparisons in this paper relate to wood, however, some obvious comparisons to concrete exist.
A strong case is made for steel poles using basic analysis. Steel poles compare favorably in the areas of cost, quality, and impact on timing.
Cost
The up front capital cost of steel poles is comparable to wood poles. There are many less tangible costs that will be discussed below, but the basic costs are already acceptable.
In our case there was some savings as a result of fortunate timing and for us the costs were less than our stock value for a similar wood pole.
Strength
Steel poles are manufactured in a Class 2, 3, or Class 5 equivalence. The key requirement of which is strength. Fortunately this is easily measured, and the basic construction of steel poles has been confirmed to be quite appropriate. Steel, as a construction medium, has a lower weight to strength ratio than either wood or concrete.
Steel is a manufactured product and therefore has many benefits over wood. Better quality assurance processes mean lower design overload factors are required. Both CSA and NESC recognize this in calling for reduced loading factors as both standards allow for 1.6 time less overload factor when manufacturing steel poles as compared to wood.
Steel poles are uniform and consistent and are not subject to warping. They are also not subject to rot or insects and woodpeckers. They do not lose strength over time.
Timing
Steel poles are manufactured using a very quick process, but are subjected to plant operations. In our case the poles were on the trucks within days of our confirming the final details. The poles were delivered from Calgary and arrived quite reasonably on time.
Another component of timing is the impact on the construction schedule. We experienced slight delays as we got used to the new poles, but the basic features of lightness and the pre-drilled holes started to provide timing reductions early in the project.
Other Benefits
Lighter Material
A steel pole weighs about half of a similarly rated wood pole, and maybe a fifth of the same concrete pole. This lightness results in a long list of benefits including reduced handling costs, and reduced risk of injury, since they are easier to control, thus reducing risk of electrical contact, and are cheaper to ship and store. For larger poles, a steel pole is easier to manage. We would need a heavier crane for wood or concrete.
The overall dimensions are somewhat smaller with the butt diameter of a class 3 - 50 ft. pole being less than 16" which is similar to wood and the pole top having a diameter of 5" or 6" versus 7" or 8" for wood.
The manufacturers of steel poles project an 80 year life span for their products, compared with 20 - 40 year projections for wood poles. Either of these numbers may be skewed in either direction and, depending on conditions, we may encounter results outside these windows. It is safe to say, however, that the performance of steel will meet or exceed that of wood and should substantially outperform it.
As environmental awareness increases, the pressure to reduce the impacts of treated wood poles will continue to rise. The future cost of cleanup and the environmental costs of continued use may very well make todayÕs wood poles unacceptable in the future.
Even concrete poles which are much "cleaner" while in-service, present a long term issue once their useful lives have expired.
On the other hand, steel poles are recyclable and will continue to retain "salvage" value even when they are totally unusable as a pole.
Steel poles are consistently clean and straight. They do not develop cracks or insect holes. They are lighter in colour and less visually intrusive. In the era of City beautification, a clean straight pole line might help to stave off an expensive underground conversion.
Other benefits include the elimination of pole fires, and the automatic provision of ground paths down the pole. Simple Riv-nut connections ensure the pole is easily attached to the neutral and to ground rods where required.
Steel poles do not shrink over time and therefore hardware does not need re-tightening and in situations where climbing is desired, standard climbing steps can be bolted to the pre-drilled holes.
The direct buried poles are placed using the same techniques as the concrete and wood poles and thus eliminate the need for concrete pole bases.
There are issues to be considered when considering steel poles. These can generally be classified into Specification, Construction and Handling, and Maintenance.
Steel poles, as manufactured by IUSI, come with several options to address users concerns about corrosion. The manufacturer is deliberately neutral on which options provide the best performance and users must determine their own preferences. Earlier pricing structures tended to suggest a "Premium" and "Economy" models but recent, revised prices have balanced the options.
The poles can come with one of two corrosion protecting coatings. The options are the traditional dipped galvanizing approach that results in a thick 30 to 50 year coating; or, the "newer" Inorganic Zinc Silicate that has been a standard for years in the protection of salt water vessels. The Zinc Silicate is a protective coating that chemically bonds to the steel, is quite flexible and durable, and is applied with sensitivity to thickness.
The Zinc Silicate is applied in house by the manufacturer while the galvanizing is handled by a variety of providers. This can have minor impacts on deliveries.
Steel poles can also be ordered with an optional heat shrink wrap-around sleeve. This option is provided for those that are concerned about ground level wear or corrosion. Again, no claims are made by the manufacturer as to the impact of this sleeve.
Since poles come pre-drilled, some effort is warranted to specify hole spacing. Each height of pole requires individual spacing drawings.
Poles must be handled carefully during transit to reduce the risk of damaging the pole coating. Measures include padded delivery trailers and using appropriate padding materials to prevent surface scratches. Also poles cannot be roughly piled or dumped on their sides along the roadways.
There is some need for field drilling to match the standard pole drawings with the real life field conditions. Some unpredictable uses include partial corners, angled guy attachments, uneven terrain and non-standard equipment. When poles are drilled, bare edges are created in the protective layers. These should be touched up with the field kits that are available for both the galvanized and the coated systems.
Because the poles are smooth and much thinner, proper tools are needed to grip the pole when placing and aligning. Rubber cover-up needs to fit well or it slides down the pole. It is not likely that a pole can be removed and reused often as the procedure to jack the pole out of the ground is likely to crush the pole and as such it is not practical for use in a temporary line.
Some degree of pole maintenance will improve life expectancies. Poles can be visually checked for rust and corrosion. If concerns arise, the base can be dug out to inspect below
grade areas. Poles will not weaken internally so visual inspection can be undertaken with confidence. Any weak areas in the coatings can be repaired with the field touch-up kits.
It would be best to inspect the poles carefully a short time after placement and to touch up any areas where the coating looks to have been damaged. Once the pole is standing and framed, there is little opportunity for further damage to occur, so inspection can be on a less frequent schedule.
At York Hydro we decided that the balance in costs and the potential long term upsides made steel poles worth further investigation. Although we felt reservations, it was clear that the only solution would be to try it out. We also had the benefit of following an Ontario Hydro trial in the Heartland Region and some small trials by other Local Utilities.
We selected Westmount Avenue in the City of York as a short street that was already slated for rebuilding, and which had the added benefit of opposite side construction. We did not have to cross the "Live" construction test yet. This design required 4 - 35 ft. poles that we ordered galvanized, and 14 - 40 ft. poles that we had coated. All poles were ordered with the drilling pattern to match that used already by Ontario Hydro. The galvanized poles were ordered with the heat shrink wrap installed.
During installation the line workers expressed mixed feelings ranging from skepticism to intrigue. The benefits of the reduced weight were obvious but we had to sort out some procedures and tools. There was also some predictable resistance to the change.
Several of our problems came from the hole spacing. Our requirements call for the transformer and secondary connections to be consistent, relative to the ground and to be almost 3 feet higher than that specified by Ontario Hydro on a forty foot pole. We also has some concerns about non-perpendicular attachments, such as at corners or for guying. These were drilled and re-touched.
During installation, we had some problems with spinning the poles once they were vertical. These were addressed through the use of the proper tools from Hastings and revised work techniques. We also had some problems with the pole butt plates falling off, and this was addressed by the manufacturer with a revised design.
We subsequently committed to install approximately 70 poles on Weston Road in a "live" construction situation. Steel poles were required in this situation due to the congestion of existing underground services (i.e. gas mains). The smaller pole butt fit into an area that was too tight for wood poles.
We arranged to rent the pole delivery trailer for a very reasonable fee and arranged local storage near the site to ensure that the poles would not be overhandled. This realized further savings in handling costs.
At first the live 16kV primary created some concern, but proper work techniques and some new rubber cover-up made the operation safe. Ultimately the smaller pole tops actually increased the clearances. This installation is on-going at this time.
Our pilot project at York Hydro has concluded that the basic pole is functional. There are still some work procedures to be ironed out and the pole specification can be expected to grow on an on-going basis.
We also have yet to determine which situations lend themselves to steel poles and which are only practical for wood.
We tend to lean toward the Zinc Silicate coating for rust protection. We base this on its historical usage in marine environments but we have no experience to justify this position.
We have not taken a position on the heat shrink wrap. It would appear to provide some ground level wear protection but we are unclear on its impact on corrosion. There is some chance it could trap moisture against the pole and thus be a negative. We will probably continue to apply it where the pole is susceptible to abrasion at ground level.
We have established our pole drilling patterns based on 10" spacing on each side, plus the following key points: 8" at top for vertical bracket, standard height of secondary at 25 feet above grade and minimum 9 feet from primary, transformer mounting points and ground Riv-nuts at standard locations above secondary, streetlight brackets 27 feet above grade.
At this time it appears that steel poles will become standard material at York Hydro for at least special applications; however, over time they could become the basic construction standard.
The potential benefits of steel poles are too great to be ignored, but the level of local Hydro Utility experience wit them has been quite low. In fact, steel has been a standard material in traffic signals, highway lighting, park fixtures, fences, barns, water towers, ships, docks and on and on, and yet first reactions to use as a utility pole is often quite negative and sometimes very emphatic.
Steel poles present no greater hazard to line men than other poles in use today, and are installed using the same basic techniques that we are using in our day to day work. In some areas of the world, steel distribution poles are already the product of choice.
The need for a more reliable and consistent pole and one that does not impact on the environment is ever increasing. Cost concerns will force a look at longer life products.
Once the designer begins to contemplate steel poles, of vital importance will be managing the reactions of others. One will have to be prepared to defend safety concerns, discuss corrosion control options, review and revise work practices, order new tools and rubber cover-ups, and carefully determine hole spacing to minimize field problems.
However, if carefully managed and once field concerns are resolved, some of the immediate advantages of the material will be apparent and the long term benefits will be achieved.
D.Thompson is a Distribution Engineer with the Hydro-Electric Commission of the City of York, Ontario. ET