Line post insulator, suspension insulator, stand off insulator requirements ensure to the insulator quality, insulator dimensions, insulator performance and insulator material and so on.
All types of the insulators shall meet or exceed the requirements of international specification in all respects and shall consist of a single piece of porcelain together with its metal parts to form a rigid assembly. Any variations in these dimensions due to manufacturing tolerances shall be indicated.
Line post insulator, suspension insulator, stand off insulator Design Criteria
◆ Manufactured, designed and tested in accordance with corresponding specifications
◆ All types of insulators shall have good mechanical, electrical and insulation performance
◆ The design shall be such that stresses due to expansion and contraction in any part of the insulator shall not lead to any deterioration. Precautions shall be taken to avoid chemical reaction between cement and material fitting.
◆ Suspension insulators shall be Clevis type ANSI class 52-4.
◆ Spool insulators shall be ANSI class 53-3.
◆ The creepage distance shall be based on the following:
a. 25 mm/ 1 kV for Dry Areas (inland)
b. 40 mm/ 1 kV for Wet Areas (coastal)
◆ Three types of Line post insulators shall be as follows:
- With total creepage distance 552 mm for 13.8 kV (Diameter of
Shed 152 mm and creepage distance is 40 mm/kv).
- With total creepage distance 825 mm for 33 kV (Diameter of
Shed 178 mm and creepage distance is 25mm/kv).
- With total creepage distance 1320 mm for 33kV (Diameter of
Shed 185mm (Min) and creepage distance is 40mm/kV).
Line post insulator, suspension insulator, stand off insulator materials
◆ The insulators shall be made of good commercial grade wet process porcelain.
◆ The entire exposed porcelain surface of the insulators shall be standard glazed and shall be brown in color. The entire porcelain surface shall be smooth and free of imperfections.
◆ The glazing of the porcelain shall be of A-Type to minimize radio interference (RIV) and corona discharge voltage.
◆ Metal parts shall be made of a good commercial grade of malleable iron, ductile iron or steel, galvanized in accordance with specification BS 3288.
◆ Portland cement shall be used as the bonding agent and for filling the gap between the porcelain and the metal parts. It must have high compressive strength to maintain the cantilever strength ratings of the insulators specified in the technical data schedule. Sulfur based cements are not acceptable.
Line post insulator, suspension insulator, stand off insulator construction
◆ The hardware shall be cemented on the porcelain with load distribution evenly throughout the porcelain. Before cementing, the hardware surface in contact with the cement shall be coated with bituminous compound.
◆ The contours of the metal and porcelain parts shall be such as to eliminate areas of high electrical stress concentrations.
◆ The insulator shall be of puncture proof porcelain constructions.
◆ The insulator surface shall be shaped and spaced for effective natural cleaning and effective use of leakage distance for desert conditions.
◆ The insulator shall be radio interference free at operating voltage
◆ All ferrous components except those made of stainless steel shall be galvanized.
◆ Suspension insulator:
a. The axial, radial and angular displacements of the insulator and their verification shall be in accordance with IEC 60383.
b. To inhibit the accelerated corrosion of insulator pin due to leakage currents, a corrosion intercepting zinc sleeve fused to the pin shall be provided at the point where the steel pin emerges from the cement.
Line Post Insulator Mounting
a. The line post insulator bottom and the stud shall be serrated to lock the stud against loosening due to line vibration as shown in drawings.
b. The stud for the line post insulator shall be hot- dip galvanized in accordance with appropriate industry standard and complete with nuts and washers for steel crossarm mounting. The size and dimensions are given in drawing.
Stand off Insulator Mounting
a. The base of the stand off insulator shall have ISO metric thread bolt holes on standard bolt circles for interchangeability and ease of mounting. Holes in top and bottom fittings shall be in line, and they shall be so arranged as to permit the use of standard hexagonal bolt heads and nuts.
b. The stand off insulator may be mounted either upright, horizontally or inverted positions.
Line post insulator, suspension insulator, stand off insulator requirements have other factors used in distribution and transmission systems made from porcelain material.
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