Station post insulators are indispensable for HV substations and related apparatus. At the 2019 INMR WORLD CONGRESS, internationally-known expert, Dr. Jens Seifert, Chairman of IEC TC 36 INSULATORS, will review the state-of-the-art of station posts, discuss technological and application challenges as well as offer his views on future developments of station posts.
Porcelain station post insulators have been applied at substations for more than 100 years and cover the voltage range from 1 to 765 (800) kV. Maximum cantilever strength classes are in the range of 20 to 30 kN. Single units can be manufactured up to a length of 3000 mm. For voltage levels exceeding 245 kV, assemblies (multi-unit stacks) are used consisting of 2 or more individual units connected by metal flanges. Standard IEC 60273 is applicable for IEC types for selection according to characteristic values. The relevant test standard is IEC 60168. Post insulators according to the ANSI standard C29.9 are defined as a ‘catalogue’ (TR types) according to characteristic values and covering types up to 765 kV. ANSI C29.9 also defines applicable tests. Porcelain station posts in accordance with IEC 60273 and ANSI C29.9 are well specified and can be ordered according to a C- or TR-Code respectively. But both standards are relatively old and need revision in order to accommodate latest technological changes and updated definitions of pollution classes as per IEC 60815-2. Modern production technologies offer high-strength designs optimized in shape, weight and shed profile. For applications under severe pollution, RTV silicone coatings can be used to improve electrical performance.
Glass station posts are also specified in IEC 60273 and consist of individual units made of glass typically assembled using cement. Complex housing profiles can be realized with this technology. Application of multi-unit glass stacked post insulators is rare at modern substations but many applications installed in the 1950s and 1960s are still in service. Under severe pollution, RTV silicone coatings can be used to improve electrical performance.
With development of composite insulators, the first composite station posts (CSPs) were introduced in the early 1980s, consisting of solid core fiber reinforced polymeric (FRP) core material and an elastomeric housing. Typical core diameters are in the range 45-100 mm with maximum diameters rarely exceeding 130 mm. Application at substations derived from early use as composite line post (CLPs) insulators, mainly in the United States. CSPs with solid core are typically applied up to 245 (420) kV. For higher voltage classes, relatively high mechanical deflections limit a wider range of application. The test standard for this product is IEC 62231 while the mechanical and electrical characteristics are defined in IEC 62231-1, which also includes the types for North American practice (ANSI). ANSI C29.19 is the relevant standard for ANSI types.
For voltage classes greater than 245 kV, height of insulators and bending moment increases. Much effort therefore must be taken to realize the requirements with solid core CSP designs (i.e. core diameters >170 mm). That leads to less cost-effective designs compared to porcelain types. Composite hollow core station posts (CHSPs) and/or hybrid station post (HSPs) insulators have begun filling this segment of application. CHSPs have already been realized for 800 kV HVDC and 1100 kV UHV applications with connection length of more than 10 m and tube diameters of 500 to 1000 mm. Bending moments of more than 1000 kNm are feasible. The hollow volume inside the posts has to be filled with an electrically inert medium e.g. foam of insulating gas. The applicable test standard is IEC 62772.
Hybrid station posts according to IEC TR 62896 are combinations of porcelain (ceramic) and composite (polymer) technology. The core of HSPs is typically made of solid core porcelain of high-strength ceramic body (C130) while the housing is made of an elastomeric material (typically LSR or HTV silicone) and by applying injection molding or extrusion process. The advantages of HSPs are low deflections of the rigid porcelain core with a high E modulus under cantilever loading. The hydrophobic silicone housing improves electrical properties under polluted conditions. Applications include large HVDC post installations and posts for disconnector switches (i.e. having low deflection requirements).
Dr. Seifert’s presentation will review the state-of-the-art of these alternative technologies, upcoming changes in standards and the ideal applications for each. An outlook is also made to future applications where use of composite station post insulators will be preferred.
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