![]() ![]() ![]() 6: (left) Coating after successful 1A4.5 test (right) Same coating but with different sample preparation procedure failed same stress.Ī more pragmatic approach is evaluating erosion resistance of a coating when applied over an insulator. 5: Set-up of inclined plan test as per IEC 60587. Referencing this test in any coating specification, therefore, requires a clear description of the protocol by which samples are to be prepared. Fluctuations show withstand results at 1A4.5, but with questionable consistency. 6 shows results for the same coating material being tested with different preparation procedures. Another approach is therefore to apply the coating over a ceramic tile. However, it is more challenging to perform in the case of coatings where less consistency is obtained due to the difficulty of pouring the coating into an appropriate mold. This test is easy to perform on LSR and HTV silicone rubber compounds that are easily molded into large sections. Silicone coatings usually meet the requirement of 1☃, 5 when using Method 1 with 6h voltage steps. 5 illustrates the test arrangement and typical results. 4.įor example, a relatively well-known test described in IEC 60587 is the inclined plan test. Several tests should be considered in this regard, including the arc resistance testing shown in Fig. The most relevant parameter here is its ability to sustain arcing without excess damage from erosion. Once the applicable physico-chemical parameters of a coating have been established, there is the need to evaluate its electrical performance. 4: (from left to right) Testing resistivity, permittivity and dissipation factor, dielectric strength and arc resistance. 3: Physical properties describing intrinsic electrical properties of coatings Fig. 3) should also be considered with the goal of establishing reference properties of the silicone used in a coating intended for electrical applications. 2: FTIR spectrum identifies constituents of silicone polymer.Īdditional physico-chemical parameters (outlined in Fig. Specific gravity is another useful indicator in this regard. FTIR and TGA procedures therefore help validate approved materials through type tests as well as ensure consistency of supply of these materials by means of sample tests. 1: Typical TGA test showing ATH content of silicone coating.įTIR analysis, by contrast, provides a spectrum where various key components are identified by their specific absorption bands (see Fig. While some coatings have neither ATH nor a substitute, multi-stress ageing tests confirm that such fillers inherently reduce risk and rate of erosion in harsh service environments. TGA is intended to demonstrate the presence and proportion of alumina trihydrate (ATH) contained in the silicone. This fingerprint must include the following: thermal gravimetric analysis (TGA) Fourier transformed infra-red (FTIR) analysis and density. In addition, CIGRE Technical Brochure 595 explains how to establish the fingerprint of a silicone coating using similar requirements to those used for polymeric housing materials. For example, one obvious test is verifying hydrophobicity, with an expectation of HC1 based on IEC TS 62073 as reference. Curing of RTV1 materials, by contrast, relies only on exposure to ambient moisture.īased on 40 years of laboratory and field experience at Sediver – a supplier of toughened glass insulators – it has been determined that selecting a coating should be based on physico-chemical parameters that influence its performance during ageing tests, whether these are type tests or type and sample tests. Most of the diverse formulations of silicone coatings now available on the market are classified as RTV2, meaning that a chemical agent is added to promote curing. Listen to Online Lecture on Specifying RTV Silicone Coatings For Overhead Transmission Lines by Jean-Marie George Selecting Coating Material Second is the coating process itself which must be carefully considered and controlled to avoid accelerated degradation in performance. First, selecting the most appropriate coating material is key to achieving lasting hydrophobicity as well as a resistance to erosion – even under severe pollution and related corona activity. This edited contribution to INMR by Jean-Marie George, Scientific Director at Sediver in France, discusses two requirements that ensure satisfactory long-term performance of a coating. As this process evolved, coating line insulators moved progressively from something performed mostly in the field to industrial scale application in specialized factories to allow for greater consistency, reliability and economy. Silicone coatings have traditionally been applied mainly to mitigate insulator contamination problems at substations but the past 25 years have seen their application to overhead lines grow significantly. ![]()
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