IEC standard 60383-1 “Insulators for overhead lines with a nominal voltage above 1000 V, part 1: Ceramic of glass insulators for a.c. systems – definitions, test methods and acceptance criteria” has not been revised since 1993, when its fourth edition was released. This standard deals with pin insulators, line post insulators, string insulator units and insulators for overhead electric traction lines. Although the standard has proven stable and is referred to frequently, the past few years have seen an increase in requests for non-standardized tests based on specific requirements by transmission system operators. The main reason for this is that some TSOs believe that existing tests are not stringent enough, as evidenced by different types of failures being experienced in service. This suggests a need to develop tougher requirements in terms of increased test duration and number of samples in combination with new test methods.
At the TC36 plenary meeting in Frankfurt in 2016, it was therefore decided to start revision of the standard and this task was assigned to a new maintenance team (MT20). A CD is to be distributed to the national committees with the aim to publish the new revision by the end of 2020. This edited Oct 2019 contribution to INMR by Dan Windmar, Convenor of IEC TC36 MT20, summarized work done by summer 2019. The work has been on-going and final content and wording will be decided by MT20 as well as the National Committees of participating countries.
Layout of Standard
The current version of IEC 60383-1 is based on the original layout when first issued. While generally well written, with many electrical, mechanical and material tests and a sampling procedure based on standards such as ISO 2859-0, -1 and -2, the layout is no longer in accordance with the current format and rules of IEC. The complete document is therefore being revised. This represents major work and the MT has had much discussion on how best to improve both the standard and its layout.
For example, several chapters in the old version, such as quality assurance, standard atmospheric conditions, etc. have been removed or heavily reduced. At the time the standard was first written, not all such information was available and therefore was included. Modern day standards however are better developed and mature and it is no longer deemed necessary to include such information in the new version. Another major change in layout will be that the cross reference tables that specify which type of tests (i.e. type, sample, routine) are valid for a specific type of insulator and number of samples to be tested has been moved from the end to the beginning of the document. The MT believes that these tables are the most vital part of the document and should therefore appear early in the document.
Proposed Revisions to Existing Test Methods
In the verification of locking system, the acceptance criterion adopted for the operation test will handle split-pins and W-clips for loads up to 650 N. Moreover, there has been discussion regarding which dye penetrant to use in the porosity test, now proposed to be specified as Astrazon. Similar discussion on dye penetrant specification and how this affects results is taking place in other IEC groups. In regard to routine visual inspection, there is also discussion on adding information regarding surface defects, particularly for glass insulators.
New Test Methods Discussed
Impulse Puncture Test in Air (Steep Front)
As discussed, the revised IEC 60383-1 will contain reference to two alternative methods for evaluating puncture withstand, i.e. an impulse puncture withstand test or a power-frequency puncture withstand test. This test evaluates puncture strength of the insulator, which depends both on design and quality of manufacturing. The section on power frequency puncture withstand test will remain more or less unchanged but an additional section is being added specifying the impulse puncture withstand test, based on IEC 61211 and illustrated below in Fig. 1. Similar discussion is ongoing within ANSI in regard to standard C29.2B, now also being revised. Test set-up, test voltage generation, measuring equipment and test procedure shall be according to IEC 61211. Number of insulators to be tested shall be in accordance with tables in IEC 60383-1 but exact quantity is still under discussion. Insulators to be tested shall be dry and clean. The test shall be performed on each unit, whereby a series of five positive, five negative, five positive and five negative impulses shall be applied (in that order), with time interval of 1 to 2 minutes between consecutive impulses of the same polarity. No impulses with reduced amplitude shall be applied between changes in polarity.
Puncture Determination & Acceptance Criteria
An insulator passes if every steep-front impulse voltage application results in external flashover and the test record or peak voltage indicator does not show a marked reduction in voltage between impulse applications. For evaluation of results from each batch under test, it is recommended that acceptance criteria be applied in accordance with IEC 61211, cl 5.8, i.e. requiring that no punctures are accepted and that if only one unit is punctured a re-test procedure shall be applied. In addition, it is now being proposed that part of the insulators tested go through the mechanical failing load test in IEC 60383-1. Also, any punctured units shall be included.
Mechanical Failing Load Test After Impulse Test
As mentioned, it has been discussed and is proposed that a number of insulators that have been tested in the impulse puncture test, e.g. 5 samples, should also be evaluated in the mechanical failing load test. The test should be done to ensure that mechanical properties have not been lost due to the electrical test.
An RIV test has been added and shall be performed on single insulator units. The test circuit and equipment shall be according to IEC 60437 and CISPR, with acceptance criterion under discussion in regard to whether a specific level should be set based on line voltage or whether a statistical approach should be used.
Zinc Sleeve Test
A section has been added specifying the zinc sleeve test to be used whenever applicable and referring to IEC 61325. A re-test procedure is being adopted in case of failure to fulfil the acceptance criteria.
This is a test required these days by many TSOs and also included in some regional and national standards. However, test procedure, test equipment and acceptance criteria need to be evaluated and discussed. In principal, the test is performed by hitting the outer rim of the shell squarely in a direction parallel to the axis of the cap and pin insulator and with specific force. Acceptance criterion can be that the insulating body of the insulator cannot rupture below a certain level. Also, release of splinters during the impact test is considered as partial disruption of the insulating body. In such cases, the result is considered as not satisfactory.
At the TC36 meeting in Busan, Korea in 2018 it was decided to include an Annex on RTV silicone coatings and requirements that are specific for this type of product. The Annex will contain general information as well as additional tests relevant to polymeric insulators that will likely be specified, e.g. adhesion, tracking and erosion, etc.
In 2016, MT20 was assigned the task of revising IEC 60383-1. The first meeting was in September 2017 and the first CD will be circulated to national committees for comment by the end of this year. There will be substantial changes in layout, partly because the old version no longer follows current IEC layouts and partly to increase readability of the document. Current test methods have been reviewed and updated where deemed necessary. In addition, a number of new test methods are being proposed.
• IEC60383-1, 1993
• Proposals for additions to IEC requirements intended to verify quality of glass cap and pin insulators, K. Halsan, I. Gutman, J. Lundengård, L. Carlshem, J. Velek, T. Condon, P. Shiel, J. Lachman, R.W.S. Garcia, B2.311, CIGRÉ 2016, Paris, France
• Impact of quality of glass cap-and-pin insulators on life cycle costs and proposals for screening tests, K. Halsan, I. Gutman, J. Lundengård, L. Carlshem, J. Velek, K. Välimaa, J. Lachman, B2.209, CIGRÉ 2014, Paris, France