Non-ceramic polymer insulators advantages

Compared with porcelain insulators, Non-ceramic polymer insulators advantages have more than ceramic insulators, such as pollution resistance and arcing distance, creepage distance and others.

Non-ceramic polymer insulators advantages

Water vapor permeation
The Silicone housing does not provide a sufficient water vapor barrier. The glassfiber reinforced resin impregnated tube consists of 70vol % glass fiber. This high content of glass is the main reason for its potential low water vapor transmission rate. The PU foam itself will absorb water up to 3% of its volume. At the time of the development of the support insulator a governmental funded research

Short term – artificial gap test
As it is impossible to guarantee either the filling being completely uniform or the foam adhering to the inside of the tube along the entire interface of the insulator. The stability of the system in a worst case scenario was simulated:
• No adhesion of the foam to the inside of the tube
• A gap between the tube and foam of 1 -2mm throughout the insulator
• Water inside the tube to 100% relative humidity of the gap space at room temperature
The basic idea was to create a layer of condensed water along the inside of the tube to trigger an internal flashover. The amount of water used in this tests was above the calculated amount which might accumulate due to the water vapor transmission rate of the tube (using Fickians law). Samples were left in an oven for 24h to vaporize the water. The parts were then quickly cooled below dew point and immediately exposed to an AC withstand test. In none of the tests an internal flashover happened. All flashovers occurred on the outside of the insulator in air. It should be noted that complete filling of the insulator and firm adhesion of the foam to the inside of the tube is still needed to provide sufficient additional safety margin.

Medium term – no flange test
Foamed tube samples of different lengths without flanges at either end were used to simulate a defect of the sealing between the flange and tube were exposed to 40ºC @ 90%rH for a total of 4000h.
During the test the samples were taken periodically to the High Voltage lab for AC flashover test.
Weight increase due to the humidity was monitored. All flashovers occurred on the outside of the insulator in air during all electrical tests.

Long term- 50.000hrs humidity test
Special samples were produced with 4mm fiber glass reinforced tubes to increase the water vapor transmission rate of the glass fiber reinforced tube. It should be noted that none of the serial products features such a thin wall – the smallest wall thickness for serial products is 8mm. Samples were tested in accordance with IEC 61462 part 7.2 - “Interface and connection of end fittings “ - which consists of a combined mechanical, and temperature stress preconditioning . Pass criteria is outer flashover during impulse test after boiling in salt water of the sample for 42h. All three samples passed this test. One unit was then exposed to the salt fog test in accordance with IEC 61227 and afterwards stored at 100% relative humidity for a total of more than 50 000 h as of today. During this storage period the sample was impulse tested infrequently. No flashover occurred inside the insulator.

 

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