03ESM00007

To produce I too

GLOBAL ESMO 2003 March 17-21,2003 -Orlando, Florida

INSPECTION AND MAINTENANCE O F WOODEN POLES STRUCTURES

Frederico Maciel Gravito - CEMIG Nilton dos Santos Filho - CEMIG

BRAZIL

E-mail: nsfilhoiii)ccmiv.com.br

Exhausts (Kg EC)

WORDS KEY Wooden Structures, Wooden Poles, Inspection and Maintenance of Overhead Transmission and Distribution Lines.

1. INTRODUCTION Wooden poles are used in the whole world supporting a significant parcel of transmission lines and distribution networks. Besides their lesser cost and weight, easiness of transport and handling, wooden poles have a long life expectation. provide great personnel safety during lme construction and maintenance. and a high Basic Insulator Level. In Brazil wooden poles bring an additional price regulation power over other types of poles. Although Eucalyptus is the predominant genre of trees used in Brazil, Australia and South Africa for the manufacture of wooden poles, the Brazilian legislation also allows the use of pinus trees (which are widely used in the USA). Eucalyptus poles are produced io Brazil from forests cultivated with this purpose, and constitute a very useh1 short-cycle renewable natural resource.

Cemig has approximately 20,500 wooden poles in 3.500 km of transmission lines (34.5. 69 and 138 kV), and around 391,000 wooden poles in rural and urban distribution networks, totaling approximately US$22.142,860 in wooden poles asset. In the past, due to the short life and low performance of its wooden poles. Cemig stopped buying them for a short period and quickly there was a raise of the prices of concrete poles. It was then verified that wooden poles can help regulate concrete poles prices. Since then, with the collaboration of Instituto de Pesquisas Tecnologicas de SHo Paulo - lPT-SP (research and technology institute of the State of Sao Paulo), ABPM (Brazilian Association of Wood Preservation), and Montana Quimica S.A. (manufacturer of wood preservatives), Cemig has carried out several research programs. lookmg forward the best techniques and the most suitable equipment to improve its wooden structures inspechon and maintenance.

The Environmental Subject

To cany out a policy of re-utilization and recycling of out-of-service poles and crosspieces, companies must be prepared to use structures as long as they still keep a minimum of mechanical conditions and to give the due destination to the non-serviceable residues, that still can

Plastic

he used by the industries of wooden accumulations, MDF. among others.

According to the Brazilian Association of Wood Preservation - ABPM, a growing tree consnmes between 18 kg and 35 kg of COz per year. The production of 1 ton of dry wood sequesters 1.8 ton of CO2 and releases 1.2 ton of Oz. In 12 years of growth a IO-meter eucalyptus pole consumes between 216 kg and 420 kg of CO2: its weight reaches 250 kg and it contributes with the sequestering of 450 kg of CO2 and with the releasing of 300 kg of 02.

TABLE I - COMPARATIVE CONSUMPI'ION OF ENERGY TO PRODUCE 1 TON OF SEVERAL INPUTS

1.800

Cement ~~

260- Block of Concrete Simple Concrete I 26

Wood 0.8 Kg EC: Equivalent kilos of coal Source: Lenec

Source Lenec - National Laboratory of Cwll Englneenng (Portugal)

2.OJ3JECTIVE This article has the objective to subsidize the activities of line and network electrical maintenance teams, and also to update them in what concems the techniques and current resources for commissioning, inspection and corrective and preventive maintenance of wooden poles. Other objective is to highlight the importance of the wooden pole use in electrical systems, its real cost. useful life and efficiency. Besides it shows a practical guide and tables. aiming at standardizing and divulging the current criteria of evaluation and maintenance of preserved wood.

3. WOODEN POLES The useful life of wooden poles can exceed 25 years of service if appropriate chemical preservatives are used and if a preventive periodic maintenance is performed on the poles in service.

26

0-7803-7917-9/03/$17.00 02003 IEEE 151

Photo I - Overhead h-ammission Lioc in Mhas Gersis, Brad

Disadvantages of Wooden Poles Some species of trees have a high natural resistance to deterioration: however they usually present a slow growth pace that is highly demanding as for the soil ccoditions and climate. In general, exposure to bad weather and contact with the soil can cause a biological deterioration. mainly by fungi and termites. In the underground area the degradation is usually more intense than the verified in the exposed p m (aerial). Woodpeckers, ants, bees, and other insects may also cause damages to the poles. Oxygen, temperature, humidity and pH are the basic factors for the development of destructive organisms in the wood. Fungi action: the wood is softened and without mechanical resistance. It can be noticed a sour smell and high humidity. The wood loosens in small pieces. It happens mainly in the pole ground line (from the ground surface up to approximately 60 cm under).

1 -. ". . . . . =.ii_ L.2.1- .-XI. -_ -..--"--

Photo ll - Ronenness rnusrd by hog& in the pole ground Line

Termites action: they usually attack the core of the wood, also destroying its mechanical resistance. They enter in the pole from the ground or through some rifts. They form their colonies in the ground close to the poles.

Photo Ill - Damages caused by termits, in the soil line

Preservative Chemical products used to preserve and to protect wooden poles and crosspieces from the attacks of fungi and termites. mainly. The preservatives can be soluble in water and soluble in oil.

PCF (pentachlorophenol) and creosote are soluble in oil. CCA (copper, chrome, arsenic) and CCB (copper, chrome. boron) are common water-soluble preservatives.

Wood Preservation There are several methods for wood preservation. such as painting (with a brush). aspersion. immersion. diffusion. etc. To preserve poles for electrification purposes. the Brazilian legislation allows only the autoclave preservation process, which guarantees a better penetration of the preservative into the wood.

An industrial wood preservation plant usually comprises autoclave. vacuum pump, pressure pump. storage tank, mixmg tank, piping, valves, apparatuses for liquid flow control. temperature control instruments, crane for moving logs, drying, preparation and storage yards, etc.

4. INSPECTION ANI) EVALUATION OF WOODEN POLES

External and internal inspection Initially evaluate the general state of the pole. from the ground to the top, checking the physical aspect of the structure, observing scratches, woodpecker holes, rifts on the bore area. fixation of screws. mechanical damages (from collisions. fire. streaks. etc). signs of deterioration and attack of insects. Register all information in a formulary or electronic collector (handheld). During the inspection, remove the least necessary healthy wood. avoiding new damages to the poles. Inspectors should not use axe, large knife. shovel, or other cutting tools.

152

External Inspection @ole base) Deterioration happens mainly in the pole ground line. The inspector should dig a ditch about 60 cm deep around the whole pole circumference in the ground line, to check the pole base. With the aid of steel brushes, clean the area to be examined removing dirt and debris.

Photo IV - Dig B ditch about 6 k m deep

With a probe. the pole is perforated and tested by removing small chips of wood. Observe if fibers in the pole ground line come unfastened, in the form of plates and test their hardness. Compare these fibers with the fibers in the healthy parts of the pole. The presence of holes and galleries may indicate attack by insects. Openings and rifts should be checked, evaluating if there is accumulated dirt inside, evidences of termites, ants and internal rottenness (hollow). After the cleaning of the area and the retreat of the deteriorated wood, measure the pole perimeter, approximately 10 an above the ground level and the remaining perimeter in the point where the circumference loss is the largest.

To control the performance of the several pole types used by CEMIG, we have developed a Table, where the percentile of loss (area loss) indicates a warning for the pole maintenance or substitution. When that percentile is reached, it is assumed that a real deterioration level and a probable mechanical compromising have been attained. The inspector must then consider the status of the pole. to decide for its substitution or maintenance. The pole status is related to its conditions and to the whole situation of the line or network. There are several factors. such as the span length, if the pole is in a urban area. if it is a highway crossing span, if there is a line angle on the pole, etc. If the decision goes for the maintenance of the pole in service. the applicable corrective and preventive procedures must be carried out.

Internal Inspection (Percussion Exam) It is a technique used for checking if there is or there is not a hollow in poles. Using the inspector's hearing

sensibility and experience it is possible to diagnose. with a little margin of error, the pole internal status. With a light hammer, beat fm blows around the whole circumference of the pole, in an area from the ground line up to an approximate height of 2 m. A clear "sound" in the beat of the hammer indicates good state and a deaf "sound" may indicate rottenness and an internal hollow. There are some sonic detectors in what sound waves are reflected by the wood in a way that is proportional to the pole sanity, showing in a specific scale the probable wood sanity condition. Those devices complement, hut they don't substitute for the inspector's experience in the percussion test with the hammer. The use of the sonic detector is a valuable help and it enriches the pole evaluation. If the evaluation with the hammer or the sonic detector signal indicates possible damages. the digging previously accomplished for the ground h e inspection will allow the use of a manual or electrical drill for the hollow or internal rottenness diagnosis. Special careful should be taken for poles with rifts. excessive humidity (mostly during the rain season), or displacement in the wood. The sound can be "deaf' in spite of there not being deterioration. what fakes the true pole situation.

Photo V - Evaluating the dimension of the hollow in the pole

Using a perforation drill or a graduated probe (stem), one can evaluate the size of the internal cavity (hollow) and the wall width of the remaining healthy wood. Knowing the hollow extension, another table can he used to suggest carrying out the pole maintenance or its substitution, depending on the verified percentile of internal loss. Sometimes, it is necessary to perforate the pole in more than a point, for best diagnosing the situation. The minimum possible number of holes should he made and the holes should be reused for the application of preservative products, if there is a hollow. All holes should be closed with bungs of treated wood (or hardwood), in order to prevent humidity and insects from entering and the core exhibition. what would favor deterioration.

153

Internal and External Deterioration The two types of losses of healthy wood (hollow and circumference loss in the ground line) can happen simultaneously in the same pole. With the dimensions of the two existent losses. it is possible to evaluate the pole condition using appropriate tables and to decide between the pole maintenance or substitution. If it is decided to maintain the installed pole, it should be executed the necessary maintenances for each deterioration occurrence.

Poles Substitution When the found defect impairs the mechanical resistance and brings rupture risks in case of overloads provoked by wind. breaking of cables, accidents, etc. it is necessary to put a new pole in service. The same defect detected in two similar poles installed in different conditions can require the substitution c d one of them and not of the other one. An initial attack: doesn't require substitution and the pole should always he indicated for treatment. A medium-level attack. can or cannot require substitution. according to the amilysis of the pole status. When the attack is intense or advanced, it will probably be necessary the substitution, although sometimes the pole can still be maintained, according to his importance and to the criterion used by the maintenance team. Besides the reduction of the circumference in the line of ground andor presence of intemal hollow, it is i:ssential, for the decision of substituting or no a pole. to evaluate his status, that basically is related to the size of the adjacent spaces. weigh of the cables: number of poles in the structure (1, 2 or 3), structures with reinforcement (same anchorages), type of the pole (light. medium. heavy, etc.), crossings (inhabited areas, highways, rivers, cable cars, railways. etc.), etc. Therefore. after of the mechanical state, the installation conditions are the main factor to defme for the freatment or substitution of the pole.

5. CORRECTIVE MAINTENANCE Defmed for the maintenance of the poles in service, for all of the deterioration levels, should be executed the corrective and preventive treatments, with the objective to paralyze the evolution of the deterioration and to maintain the satisfactory mechanical condition of the structure. The treatments, when correctly executed, should guarantee the current mechanical resistance of the pole. at least for the period recommended hy the preservative manufacturer. When the mishap limits just to the base of the pole (close to the ground lime) a practical solution is a new healthy piece of pole, in the place of the deteriorated hase of the old pole. This installation has smaller cost, allowing to reuse poles removed yet in good conditions, besides representing a smaller risk of accidents and agility in the execution of the repair, although visually unsatisfactory.

Snperficial treatment Accomplished in ground line (foot-of-pole), through brushing of preservative liquid or pasty, associated a dressing for contention and concentration of the product. The efficiency of the superficial healing treatment also varies with the conditions of the soil, species of the wood, used amount. preservative type and application form.

Internal treatment Liquid preservative used for possess larger penetration power. larger diffusion interns and stability. The product is injected through the holes accomplished in the inspection and same some add, if necessary. All of the holes need to close with bungs. Always follow the instructions and periods recommended by the manufacturers.

Photo VI - Applyinp the insecticide and fungicide internally in the pole.

Soil Treatment We accomplished with syrups liquid insecticide. It is watered the walls and the bottom of the digging and it goes if closing the gutter, heating the earth and watering from a uniform way to the level of the soil.

Photo VI1 - Applying the insecticide syrup in the soil, in the outline of the digging of the pole.

154

6. PREVENTIVE MAINTENANCE

Basically it is the same procedures accomplished in the corrective interventions. Even the poles that are not deteriorated may undergo, beginning at a certain deterioration status, as a prevention procedure. a preservative treatment in the ground lime. mainly if the pole is installed in areas of great incidence of termites andlor fungus. New lines can he treated during the installation. by prevention when the area has a record of presence of termites, fungus or both. For the combat of termites we make a chemical barrier, using the treatment of the soil. For killing fungus, fungicide is applied with a cover (dressing). The fvst next treatment should he made according to the manufacturer's recommendations or experience in the area in relation to the wood destructive of organisms. New poles, poles stored by long periods and poles already used must receive a superficial treatment with dressing and soil treatment as a prevention, in the installation. mainly if the area has a relevant record of termites and

In areas of high aggressiveness, the intervals can be reduced, if this need is verified.

7. OBSERVATIONS AND CONCLUSIONS

fungus.

Insecticide and fungicide treatments require the use of additional individual safety equipment. necessary to the personnel and environmental protection. It is always necessary to strictly obey the manufacturers' instructions for the application of the products. All suitable treatments should he redone periodically. as recommended by the manufacturers and as for the level of aggressiveness of each area. During the inspection and maintenance procedures, the termites houses close to the structures should be destroyed. Even when it doesn't eliminate them completely, this action will debilitate the colony. easing the attack by ants (natural enemy) and other termites predators. Poles recently installed have reduced useful life. if there is any contamination in their site. The whole remaining material of the substituted poles should not be left around and the digging area should he clean with chemical product for the soil. avoiding the contamination of the new pole. Rifts, displacements, and even small intemal hollows should be treated as way of prevention with insecticides and fungicides. Only the employees really involved with the application of the preservation products should he at the work site during the preserving operations. No drinking, eating or smoking is allowed during the handling of the preservation products. It is always necessary to wash hands and face before drinking, smoking or eating after the operation. It is also necessary to maintain clean the tools and individual safety equipment.

The efficiency of an inspection and maintenance program depends on the inspector's ability in interpreting the conditions found. during the inspection. Only with the correct execution of the preventive and corrective maintenance routines, as long as with a centralized control of the several actions and of the plant characteristics, one can control facilities status and avoid assets decreasing. Before beginning any program of maintenance of wood poles. there should be a rigorous practical training, to qualify technicians and minimize the diagnosis divergences among inspectors ahout the same pole. The continuous recording of the poles sanity state observed in each inspection in the inspection notes, should gather the largest possible number of information on the inspected poles. Such records should he centralized. constituting a report (database) that it will he useful in the attendance and in the evaluation of the poles in service. If the project data are available. they can be useful in the analysis of the deterioration level, because sometimes the installed poles possess mechanical characteristics very superior to the requested for the project. In that situation, the over dimension of a pole can alter the diagnosis. Finally, after the treatment andor another treatment operation, each pole should receive an identification tag or plate containing the treatment type and the date to feed that control database.

8. REFERENCES

[ l ] - "lnspepio e Manutenqio de Postes de Madeira" - 30.000 - EG/MN - 042b - CEMIG - Junho de 2001. [2] - "Envelhecimento Acelerado de Postes de Madeira" - 02.1 11 - STINT2 - 005 - CEMIG - Fevereiro de 1993. [3] - "Experidncia de Tratamento Cupinicida de Solo na LT Dores do Indaid - Leandro Ferreira - 69 kV" - 30.000 - STDN3 - 010 - CEMIG - Agosto de 1995. [4] - "SeminLio Intemo de Postes de Madeira - Informes Tecnicos" - 30.000-STDN3-009 - CEMG - Agosto de 1995.