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03ESM00007
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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.
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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.
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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.
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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.
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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.