HV AC Switchgear

Two important factor in high voltage switchgear insulator according to IEC

  1. Minimum distance between sheds:
    In left figure factor “c” is the minimum distance between adjacent sheds of the same diameter, measured by drawing a perpendicular from the lowest point of rim of the upper shed to the next shed below of the same diameter. Minimum distance between sheds is one of the more important characteristics for insulator profile evaluation. Shed-to-shed arcing for small shed spacing can negate any effort to improve performance by adding creepage distance.
  2. In right figure factor “d” is the straight air distance between two points on the insulating part or between a point on the insulating part and another on a metal part. l is the part of the creepage distance measured between the above two points. l/d is the highest ratio found on any section, for example on the underside of a cap and pin insulator. Creepage distance versus clearance is a more localized check of the risk of bridging by arcs when dry bands or uneven hydrophobicity occur. It is also important in avoiding localized pollution buildup in deep and narrow sections of the profile.
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