Nuova Via di Piano Comprensorio Vulcano
Sesto San Giovanni, MI 20099 Italy
Tel. 02-24105.001
IS 2653 GB
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3.3
Storage conditions
The bushings when are not in service have to be store indoor (above -5° degree C); especially in extreme
weather condition (+40° to -40/50°) it is forbidden to store them outside even for a short period (mandatory to
fulfil warranty conditions).
It is necessary that all the crate is placed inside a suitable warehouse and that a periodical check of the
bushing, the gas pressure and of relevant accessories is activated (see Chapter 5.1). The recommended
timing is six months.
4
Technical characteristics
PWS and PWHS bushings are based on gas technology (pure SF6 or SF6-N2 mixture). The electric field is
controlled by suitable electrodes that are placed inside and outside the bushing. The internal electrical strength
capability is ensured by the gas density, while the external withstand capability is ensured by composite
insulators of adequate length and creepage distance.
The bushing is made by two sections, the indoor and the outdoor side, that are designed to withstand the
different environmental conditions present inside and outside the valve building.
The bushing is designed and tested in accordance with the IEC 62199 and IEC 60137 standard.
Each section is based on:
•
A composite insulator with silicone sheds.
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The internal shielding arrangement.
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An internal aluminium tube conductor.
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The top flange with the line terminal.
•
The top toroidal electrical shield.
The two sections joined by the central flange make the complete bushing.
The sealing joints between the parts are designed to minimize the risk of gas leaking by using the double
gasket concept. This means that the sealing is ensured by two concentric ‘O ring’ gaskets placed in separate
grooves.
The bushing is designed in accordance to the customer requests with different environmental conditions and it
can operate at low temperatures down to -50° C when filled with pure SF6 gas.
The solution based on gas technology offers the following advantages:
•
Simple design.
•
Lower mass compared with equivalent solution based on solid insulation. This means less risks in case
of earthquake.
•
Less different materials that reduces the risks due to DC and PR stresses.
•
No aging of the main (gas SF6 or SF6 N2 mixture) internal insulation.
•
Fast production and delivery time.
•
Full dry explosion-proof solution.
•
Limited maintenance and possibility for on line monitoring of the main insulation through gas pressure
control (i.e. density control).
The bushing can be installed on the wall with different angles from the horizontal, as previously agreed.
