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Composite solid core support insulators,station post insulators

Station post insulators also called Composite solid core support insulators made from silicone rubber used for rated voltage range 10kv to 1000kv for substations.

Composite solid core support insulators,station post insulators

Standards for station post insulators
Hollow core insulators are covered by IEC 61462 Composite hollow insulators – “Pressurized and unpressurized insulators for use in electrical equipment with rated voltage greater than 1 000 V “–. This standard however does not cover support insulators. Composite solid core support insulators are covered by IEC 62231-1, Ed. 1.0: “Composite station post insulators for substations with ac voltages greater than 1 000 V up to 245 kV”. This means that a hollow core support insulator would be a new type which is not covered by any of the existing international standards.

Filler options
The biggest challenge of this project was to identify a filler material for hollow core support insulators. Several options were investigated. Both porcelain and composite hollow core insulators were installed many years ago using air as filling materials. However, catastrophic failures caused by moisture ingress and inner flashover raised questions about the reliability of this type. A solid insulating filler material would be a great way to deal with any issues regarding inner electrical strength, leakage currents etc. However high cost and weight would not allow solid materials for an economic solution. A liquid insulation material provides a similar situation but requires special attention to solve issues like thermal expansion and leakage. Pressurized gas filling is well known for equipment insulators and has been common practice for HV breakers and Gas Insulated Switchgear (GIS) since the mid sixties. A support insulator follows the ambient temperature unlike applications where the insulator is frequently heated from the inside because of the resistive losses in the conductor due to load. Considering the mechanics of water vapor transmission this phenomena must be taken into consideration when dehydrating fillers are applied.

Foam for Composite solid core support insulators
Foam looked attractive to solve the issues as explained above. However little experience was available in the world of high voltage power products to answer some of the questions associated with foams like electrical strength, water / vapor absorption , mechanical behaviour during temperature cycling , application, long term stability etc. Polyurethane based closed cell foams appeared to be a good potential candidate. Studies carried out at the University of Darmstadt , published in 1989 indicated the potential suitability of this material as a filler. The selected PU foam provides a good thermal stability at high and low temperatures. Samples of the foam selected were tested to prove that the AC breakdown voltage would consistently be above the maximum to be expected stress. Electric field calculations showed that the electric stresses in the foam would not exceed the stresses in air on the outside.

Composite solid core support insulators are also called solid core post insulators used for any voltage electrical systems, such as station post insulator can be used in insulator string including two or more piece insulator.

 

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