SITGES-BARCELONA, SPAIN INSULATOR …...2017 INMR WORLD CONGRESS SITGES-BARCELONA, SPAIN INSULATOR...

2017 INMR WORLD CONGRESS SITGES-BARCELONA, SPAIN

INSULATOR REQUERIMENTS: DESIGN CRITERIA, OPERATION PARAMETERS AND

STANDARDS REVIEW

JAVIER GARCÍA TECHNICAL AND PRODUCTION

MANAGER

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CONTENTS

2017 INMR World Congress November 5-8, Barcelona-Sitges,

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q  INTRODUCTION q  MECHANICAL CONSIDERATIONS q  ELECTRICAL CONSIDERATIONS q  SELECTION IN POLLUTED AREAS q  POLLUTION TESTS STANDARDS q  INSULATORS TESTING STATIONS q  INSULATORS CORROSION q  OPERATION PARAMETERS q  ESTIMATED END OF LIFE q  CONCLUSIONS

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INTRODUCTION

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•  In the market, it could be found many different types of insulators for OHTL: -  Glass or porcelain string insulators, -  Long-rog insulators, -  Composite insulators.

•  Inside of each insulator type there is a wide range of: -  Designs, -  Qualities, -  Materials, -  Prices.

•  Besides the market offers different alternatives to improve the performance of the insulator on polluted areas:

-  Different profiles: Antipollution, Open-profile, Outerib… -  Silicone coated insulators. -  …,

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INTRODUCTION

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•  What is the best material? •  What is the best design for a particular environment? •  What criteria could be taken into account in the

selection of the material?, •  What parameter could be taken into account for

service evaluation? •  How to estimate the end of life of the insulator?

THERE IS NO SIMPLE ANSWER TO THESE QUESTIONS.

But it is possible, at least, to establish the different steps to be considered for evaluation and comparison of the different solutions.

•  I N S U L AT O R SELECTION

•  OPERATIONS PARAMETERS

•  END OF LIFE STUDIES

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MECHANICAL CONSIDERATIONS

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Consequences of a mechanical failure

•  Specified Mechanical Load (SML) > 2 x maximum working load •  IEC 60383-1 & IEC 61109 Mechanical test, such as Type & sample test. •  IEC 60797 stablishes the mechanical residual test methods and acceptance criteria for

glass or porcelain string insulators with the dielectric broken part.

FUTURE WORK: IEC 60383-1 ongoing revision: •  Include mechanical residual test, like a type test.

Loss of leakage distance

Conductor fall

This depends on the design of the insulator.

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impulse withstand/flashover and

dry power frequency characteristics

Arcing distance

ELECTRICAL CONSIDERATIONS

Creepage distance

Insulator diameter

Shed inclination / Shed diameter / Shed spacing

•  IEC 60071-1 recommends the associated withstand voltages with the highest voltage for the equipment

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SELECTION IN POLLUTED AREAS

Last edition of series IEC TS 60815 has developed new techniques for the selection and dimensioning of high voltage insulators in polluted areas.

Three approaches recommend to select suitable insulators based on system requirements and environmental conditions: • Approach 1: Use past experience • Approach 2: Measure and test • Approach 3: Measure and design The applicability of each approach depends on available data, time and economics involved in the project.

Determinate the most efficient insulation AIM

1st step. Determination of SPS (Site Pollution Severity) •  From ESDD & NSDD for type A pollution •  From SES (Site Equivalent Salinity) for type B pollution 2nd step. Determination of the Unified Specific Creepage Distance (USCD) reference.

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SELECTION IN POLLUTED AREAS Choice of profile – glass and porcelain insulators

•  Different types of insulators and even different positions of the same insulator type may accumulate pollution at different rates in the same environment. In addition, variations in the nature of the pollutant may make some shapes of insulators more effective than others.

•  IEC TS 60815-2 - Table 1 shows a brief summary of the principal advantages and disadvantages of the main profile types with respect to pollution performance.

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SELECTION IN POLLUTED AREAS Profile suitability – glass and porcelain insulators

•  IEC

IEC TS 60815-2 - Tables 2 & 3 give

simple merit values for porcelain and glass insulator

profiles.

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SELECTION IN POLLUTED AREAS Choice of profile – glass and porcelain insulators

IEC TS 60815-2 & IEC TS 60815-3 give profiles parameters to take into account for glass and porcelain, and polymer insulators respectively: •  Alternating sheds and shed overhang; •  Creepage distance versus clearances; •  Minimum distance between sheds; •  Spacing versus shed overhang; •  Shed angle; •  Creepage factor.

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POLLUTION TESTS STANDARDS IEC 60507 – IEC 61245

Pollution tests on glass and porcelain insulators on a laboratory could be carried out for two main objectives:

•  To obtain information about the pollution performance of insulators (comparison of different insulator types/profiles)

•  To check the performance in a configuration as close as possible to the in-service one.

Two categories of pollution test methods are recommended:

•  Salt fog method, in which the insulators are subjected to a defined pollution degree.

•  Solid layer method, in which a fairly uniform layer of a defined solid pollution is deposited on the insulators surface.

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POLLUTION TESTS STANDARDS IEC 60507 – IEC61245

IMPORTANT: These IEC laboratory standardized pol lut ion test methods are not applicable for: •  composite (polymeric) or •  RTV-coated insulators.

A proposal for a test method for art i f ic ia l ly pol luted p o l y m e r i n s u l a t o r s i s covered by the recent CIGRE TB 555.

In the case of naturally polluted insulators removed from the service, a recent CIGRE TB 691 (WG D1.44) “Pollution Test of Naturally and Artificially contaminated insulators” summarizes the recent experience with so-called rapid flashover test methods: • Rapid Flashover Test (RFO, based on IEC 60507 solid layer test). • Quick Flashover (QF, based on IEC 60507 salt fog test).

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INSULATORS TESTING STATIONS

•  Many variable environmental parameters which influence an insulator’s behavior over its lifetime are difficult to simulate artificially and, moreover, to accelerate.

•  Thus, the validity of laboratory tests is often questioned as the procedures adopted may not take into account significant factors which would be encountered in service or others may be over-emphazised.

•  Involving a longer test duration. • Requiring care in the correct

interpretation of the test data.

The evaluation of insulator performance in naturally polluted outdoor test stations is becoming more important and popular

• The results tend to be accepted with more confidence. •  It is also a good tool for new insulation technologies, in which there

is yet no technical or normative specifications for its testing or characterization.

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INSULATORS TESTING STATIONS - Goals

•  To compare the performance of insulators of different design. •  To compare the performance of insulators from different manufacturers. •  To dimension insulators for a particular environment or application. •  To examine the behavior of insulators of different dielectric materials. •  To compare the performance of insulators in different orientations. •  To explore the effects of specific parameters, such as profile geometries or insulators

diameters. •  To identify possible weaknesses or failure mechanisms of an insulator design. •  To estimate the life expectancy of various insulators. •  To serve as a qualification test for potential suppliers. •  To establish the effectiveness and life of insulator treatments, such as washing,

greasing, silicone rubber coating, shed extenders, etc. •  To assess the performance of other outdoor equipment insulation, such as transformer

bushings, surge arresters, cable terminations, etc. La Granja Insulators tests - Permanent insulator research

station at Martigues

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INSULATORS TESTING STATIONS – 4 types

R e s e a r c h station

In-service test structure

Simplified, on-line station

Mobile test stations

Monitored: •  Leakage current activity •  Climatic effects and •  Pollution severity are usually Inspection: •  Visual examination •  Hydrophobicity

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INSULATORS CORROSION

•  Chapter 26 IEC-60383-1 standardizes the minimum average coating mass for the metal fitting of the insulators: 600g/m2 (85µm).

•  This value could increase until 140µm for insulators to be installed on very high corrosion areas. This permits to increase the estimated end of life.

Zinc thickness vs. service live

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INSULATORS PIN CORROSION •  The zinc sleeve is galvanically positive and has a large

potential difference from iron. •  It works like a sacrificial electrode at the cement boundary

where the current flows.

FUTURE WORK: IEC 60383-1 ongoing revision : Include Zinc sleeve test similar to current mentioned

on IEC 61325 (DC suspension insulators).

Zinc sleeve posi1on

Pin without zinc sleeve on high

corrosion area a8er several years in

service

IEC 61325 requirements

Improved requirements

B o n d e d area 80% 95%

Z i n c purity 99,8% 99.95%

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OPERATION PARAMETERS

DATABASE •  Type / Sub-type of string; •  Type of insulation: Glass, porcelain, composite, coated

glass, etc. •  Sub-type of insulator: Standard profile, pollution profile… •  Number of insulators per string; •  Insulation manufacturer; •  Insulator traceability data (Production order, production

date…) •  Standard; •  Installation year; •  Silicone manufacture / applicator; •  Estimated end of life •  Degradation environment: Normal, hard and very hard.

MAINTENANCE INDICATORS •  Number of faults •  Insulator breakage rate •  Washing frequency

- MAINTENANCE DECISIONS - REPLACEMENT OF THE INSULATION

- COMPARISON OF THE DIFFERENT TYPES OF MATERIALS, PROFILES AND MANUFACTURERS QUALITY.

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required to ensure high long term

reliability Balanced design

parameter Choice of material Control / Mastering of quality & manufacturing processes

This document stablishes a testing sequence with a number of non-destructive tests as:

•  Visual tests (e.g. degree of corrosion), •  Dimensional test, •  Thermal test, •  Thermal-mechanical tests.

These first series of tests are followed by destructive mechanical tests.

ESTIMATED END OF LIFE – GLASS AND PORCELAIN INSULATORS (1)

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ESTIMATED END OF LIFE – GLASS AND PORCELAIN INSULATORS (2) A probability diagram based on normal distribution is used to analyze the failing load test results and compare with several “reference scenarios”

Example: reference scenario F1 The reductions in strength are not representative of good quality products. Age and TMP-test have only negligible influence on good products.

The failing load characteristics are represented by: • A dashed ►insulators sample tested when new. • A solid line ►insulators as-received from the line. • A dashed/dotted line ►insulators submitted to the

Thermal-Mechanical Test (TMP-test) The SFL (Specified Failing Load) ► solid vertical line.

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ESTIMATED END OF LIFE – COMPOSITE INSULATORS

•  Different methods, philosophies and tools are describe. They enable a conclusion regarding the residual lifetime of composite insulators of the same age and design family.

•  The document also gives guidelines in case of a failure investigation, a unit recognized as high risk, and the evaluation of units for research.

Recommended sequence of tes1ng

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CONCLUSIONS •  The selection of the insulator type is not a simple job, especially if the insulator will

be installed in a high polluted area. •  Numerous documentations (IEC Standards, CIGRE Technical Brochures, papers…)

are available to help on the selection of the most appropriate insulator, on the monitoring of the behavior in operation and on the determination of the estimated end of life.

•  Different solutions are available to improve the insulator performance on high corrosion areas.

•  Several factors must be taken into account on the insulator type selection: • More effective design/material; • Maintenance costs: Inspection cost, cleaning cost, replacement costs, … • Expected service breakage rate to be guaranteed/certified by the supplier; • Severity of consequences in case of failure (mechanical breakage, electrical failure,…); • Expected end of life.

2017 INMR WORLD CONGRESS SITGES-BARCELONA, SPAIN

THANK YOU FOR YOUR ATTENTION!

JAVIER GARCÍA TECHNICAL AND PRODUCTION MANAGER

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