Experience in the Evaluation of Polymeric Insulators for Distribution Systems in Medium Voltage...

Experience in the Evaluation of Experience in the Evaluation of Polymeric Insulators for Distribution Systems in

Medium Voltage through a ed u o age oug aNatural Laboratory

Author: Augusto AbreuVenezuelaVenezuela

São Paulo, November 2010

Content

Introduction. E l ti M th d lEvaluation Methodology.Results.Conclusions and Recommendations.

IntroductionIntroduction

Therefore, this research develops aNatural Lab.

“Caño Sagua”

Therefore, this research develops amethodology to evaluate different designsof polymeric insulators (silicone rubber)suspension type with galvanized steelsuspension type with galvanized steelhardware, aluminum and polymer coatedin a natural environment.

For this, a specific area was availablewhere environmental conditions are themost severe on the west coast of Zuliamost severe on the west coast of ZuliaState, located north of the VenezuelaGuajira, and establishing it as a NaturalLaboratoryLaboratory.

Salt Contamination Corrosion Sand

Blasting+ +Contamination Blasting

Evaluation MethodologyEvaluation Methodology“Natural Lab”

Evaluation Methodology (Cont )Evaluation Methodology (Cont…)

“Polymer and Hardware Visual Inspection”

Evaluation Methodology (Cont )Evaluation Methodology (Cont…)

ResultsModel “A”

The insulators used weremodel DS-28 established inmodel DS-28 established instandard ANSI C29.13, withleak distances from 550 mm to660 mm and with galvanized660 mm and with galvanizedsteel hardware with a minimumof 95 microns thick.

In the case of insulators withexposures of 4 years, hardwarewere found in an advancedstate of deterioration.

With regard to polymeric material, it did not present any typef d d ti d b i i l diti I l tof degradation and being in regular condition. In general terms,

with the results obtained with this model of insulator, it can beconcluded that in the northern zone of Zulia this insulator wouldhave a useful life of approximately 5 years of hardwarehave a useful life of approximately 5 years of hardwaredegradation due to corrosion.

Results (Cont…)( )Model “B” After 18 months installed, a visual

inspection found a number of deep cracks,breakage and wear of polymeric materialbreakage and wear of polymeric material.

Of the cuts made it was detected that theleakage current circulates between thefiberglass bar and the polymer coat (B-2, B-3 and B-5).

Based on the gathered evidences theBased on the gathered evidences, thebest hypothesis raised for this crack is thatbecause of the mechanical strains thepresent seal brakes between the galvanizedsteel buttonhole and the polymeric cover,causing the entry of moisture and causingpartial discharges between the polymericlayer and the fiberglass barlayer and the fiberglass bar.

Additionally, when the insulator wassectioned is was found an asymmetry in theinjection of the polymeric cover (B-4).

Resultados (Cont…)( )Model “B” (Cont…)

B-1 Galvanized Hardware.B-2 Stainless Steel Hardware.

Resultados (Cont…)( )Model “C”

The exposure time of thisinsulator was 4 years. It wasutilized an insulator model witha leak distance of 950 mm. Theintention of testing this designintention of testing this designwas to subject the aluminumalloy hardware to the actualconditions of the area.

With respect to thepolymeric material present apoor condition as wasobserved erosion andobserved erosion andpolymer separation betweenthe cover and hardware. Forthis reason it is not convenientto use insulators with hardwarepartially covered.

Conclusions and Recommendations (Cont…)

For the case evaluated and depending on the resultsobtained, it was decided to reduce the leak distance of 863.60mm used with two ceramic bells to 550 mm with a polymericinsulator without the need to do preventive maintenance (wash).

The use of insulators with galvanized steel hardware with 95microns thick for the entire northwestern region of Venezuela,except for the region of La Guajira, where it is recommended theexcept for the region of La Guajira, where it is recommended theuse of polymeric insulators with aluminum alloy hardwarebecause of the high levels of corrosion.

Conclusions and Recommendations (Cont…)Conclusions and Recommendations (Cont…)Model “A” Model “B” Model “C”

It is recommend the application of the methodology developed in

this work in regions of the world where environmental conditionssuch as environmental pollution, corrosion and sand blasting arepresent in an extreme way, and it is required to implement newdesigns for polymeric insulators, in order to detect faults andg p yimprovement points before mass implementation.

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