3.5 Static contact angle measurement
In order to estimate the hydrophobic properties of the housed
insulating materials, the static contact angle was measured on
samples 3 and 4: ethylene-propylene diene monomer (EPDM)
and SiR surge arresters, respectively. The measurements were
performed immediately after finishing a salt-fog cycle on a
surface cleaned by using ethylic alcohol. The evaluation
was done on the top surface of the sheds located on the top
and in the middle of each surge arrester: sheds no. 1 (top)
and no. 12 (middle) for sample 3 and sheds no. 1 (top) and
no. 11 (middle) for sample 4.
Fig. 7 shows the trend of the static contact angle as a
function of ageing test time for EPDM and SiR surge
arresters. The hydrophobicity is similar at the different
shed positions for the same apparatus, but the behaviour
is different for EDPM and SiR material. On the EDPM
surge arrester, the hydrophobicity decreases drastically
after 3000 h of testing. This hydrophobicity reduction is
attributed to polymer degradation caused by the salt fog
conditions and electrical stresses. On the other hand, the
SiR arrester did not lose hydrophobicity during the test.
According to visual observations performed around 2500 h
of testing, the SiR surge arrester showed higher deterioration
than the EPDM surge arrester. After this testing time, its
deterioration almost did not grow, while on the EPDM
surge arrester, it grew significantly. However, the contact
angle on SiR did not change very much during the whole
test as it does on EPDM insulating material. It can be said
that the static contact angle does not give enough
information about the ageing process in SiR as it does in
EPDM surge arrester.
3.5 Static contact angle measurementIn order to estimate the hydrophobic properties of the housedinsulating materials, the static contact angle was measured onsamples 3 and 4: ethylene-propylene diene monomer (EPDM)and SiR surge arresters, respectively. The measurements wereperformed immediately after finishing a salt-fog cycle on asurface cleaned by using ethylic alcohol. The evaluationwas done on the top surface of the sheds located on the topand in the middle of each surge arrester: sheds no. 1 (top)and no. 12 (middle) for sample 3 and sheds no. 1 (top) andno. 11 (middle) for sample 4.Fig. 7 shows the trend of the static contact angle as afunction of ageing test time for EPDM and SiR surgearresters. The hydrophobicity is similar at the differentshed positions for the same apparatus, but the behaviouris different for EDPM and SiR material. On the EDPMsurge arrester, the hydrophobicity decreases drasticallyafter 3000 h of testing. This hydrophobicity reduction isattributed to polymer degradation caused by the salt fogconditions and electrical stresses. On the other hand, theSiR arrester did not lose hydrophobicity during the test.According to visual observations performed around 2500 hof testing, the SiR surge arrester showed higher deteriorationthan the EPDM surge arrester. After this testing time, itsdeterioration almost did not grow, while on the EPDMsurge arrester, it grew significantly. However, the contactangle on SiR did not change very much during the wholetest as it does on EPDM insulating material. It can be saidthat the static contact angle does not give enoughinformation about the ageing process in SiR as it does inEPDM surge arrester.
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