· Material (Housing, FRP, Metal)
· Shed design
· Sealing between end fittings and insulating body

· Smooth sheds
· Under rib sheds
· Different shed diameters of both kinds (130 – 202 mm, 5.1 – 7.95”)
· Different shed thickness

a) FRP Rod:
· Hydrolysis resistance
· Brittle fracture resistance - For more informaition, please visit our Download Center and read our Technical Paper entitled: “FRP Rods for Brittle Fracture Resistant Composite Insulators”
· Intrinsic mechanical and electrical strength
· Void free - For more information, please visit our Download Center and read our Technical paper entitled: “Quality Requirements of Fibre Reinforced Polymer Materials for HV Composite Longrod Insulators”
b) Housing material:
· Hydrophobic - For more information, please visit our Download Center and read our Technical Paper entitled: “Hydrophobicity effect of silicone housed composite insulators and its transfer to pollution layers“.
· Ability to maintain permanent hydrophobicity transfer effect
· High UV resistance
· High corona resistance
· High T&E resistance (HC=2)
· High power arc resistance (HL=2)
· High voltage water diffusion resistance (HD=2)
· (In)flammability Class FV0 in accordance with IEC60707
c) Steel parts:
· High strength steel of controlled quality
· Suitable for compression technology
· Hot dip galvanized zinc coating in accordance with ASTM153A

No. The IEC60815 is only for ceramic and glass insulators. Currently, a revision of IEC60815 is under preparation in IEC WG with an additional part for non-ceramic insulators that also contains information and guidance for composite insulators with silicone rubber housing. This additional part of IEC60815 will also be applicable for the choice of the creepage distance for NCIs dependent on the pollution severity. Until the revised publication of IEC60815, we recommend to choose the same specific creepage distance for silicone composite insulators as for ceramic insulators. This design detail is based on our past experience and is also confirmed by several publications (STRI).

Under rib sheds have a longer creepage distance per shed (compared with smooth sheds), which allows insulator designs with long creepage distances and short connecting lengths. Further, radial positioned under ribs effect as reinforcing parts that gives additional stiffness to the sheds (avoiding distortion). Due to the hydrophobicity transfer effect, under rib sheds behave excellent even under dusty pollution conditions. This is confirmed by the service experience obtained from insulators installed under various pollution conditions (desert, marine desert, tropical etc.) worldwide.

In most cases, the pollution behavior is similar to that of smooth sheds with the advantage of longer creepage distances per shed. The “creepage distance quality” is nearly the same because of the hydrophobicity transfer effect. In general, polymeric insulator pollute stronger than ceramic or glass insulators because of the electrostatic potential of polymers, but the pollution layers will become hydrophobic soon by encapsulation of LMWs (hydrophobicity transfer effect). The under ribs are not very deep so that massive accumulation of pollution media is not possible. The accumulated layers will become hydrophobic soon so that the provided larger creepage distances will not be reduced by pollution.

The sealing is important to avoid water/moisture penetration into the end fitting area. Water can lead to corrosion of the inner end fitting parts and in combination with acids to brittle fracture (if E-glass fibres are used for the reinforcement of the FRP rod). In general, moisture penetration into the end fitting areas means a weakening of the connection between core and metal end fitting.

The sealing must be permanent elastic and permanent sticking to metal, HTV silicone and FRP material. This cannot be reached with RTV silicone materials. For RODURFLEXâ Insulators a special silicone agent is used successfully since 20 years that fulfills these requirements.

Corona on housing materials should be avoided by using suitable grading and corona protection devices. On the other hand, HTV silicone rubber used for RODURFLEXâ Insulators has a very high corona resistance that can be tested with simple corona test devices. The electrical design field stresses on silicone surfaces should not exceed a value of 1kV/mm permanently.

The electrical design field stresses on silicone surfaces should not exceed a value of 1kV/mm permanently. To fulfill this requirement, corona and grading rings should be used.

a) Recommended Corona rings/Grading rings:
· Rings recommended for system voltages greater 72.5kV (in most cases, for voltage up to 145kV, the corona rim at the RODURFLEX end fittings provides a good protection)
· = 170kV: small 160mm corona ring at high voltage (hot) end fitting
· >170kV: 350mm corona ring at high voltage (hot) end fitting
· > 275kV: 450mm corona ring at high voltage and 350mm at earth end
b) Arcing devices:
· the kind of arcing devices depends on the short circuit currents/times required for the insulator sets. Arcing devices should be used for short circuit currents greater than 16kA/0.5sec to avoid inadmissible heating and deterioration of the end fittings.

RODURFLEX® Insulators are very “silent” concerning RIV. The insulators have very low RIV values. The RIV performance only depends on the kind of insulator set hardware and corona/grading rings. If the recommended rings are used, maximum RIV values in accordance with ANSI C29.12, are fulfilled.

Material:
· HTV silicone must have high corona performance/resistance
Recommended Corona rings/Grading rings:
· Rings generally recommended for system voltages greater 72.5kV
· = 170kV: small 160mm corona ring at high voltage (hot) end fitting
· > 170kV: 350mm corona ring at high voltage (hot) end fitting
· > 275kV: 450mm corona ring at high voltage and 350mm at earth end