Research Information System
5. ULUSLARARASI MARDİN ARTUKLU BİLİMSEL ARAŞTIRMALAR KONGRESİ, Mardin, Turkey, 15 - 16 January 2021, pp.62-63
The
dielectric strength, or breakdown voltage, of transformer oil measures its
ability to support non-defective electrical voltage. Since these oils must
insulate under high electrical potential, a significant reduction in dielectric
strength means that the oil will no longer perform. A decrease in dielectric
strength may be due to the presence of contaminants such as water, conductive
particles, oil degradation by-products, residues, and cellulose paper
breakdown. Dielectric strength can be determined relatively simply by applying
an increasing proportion of AC voltage between two electrodes immersed in
transformer oil. It is important to detect failure in transformer oil early, as
it helps to further assess the health of the transformer and prevent further
deterioration of the transformer. Determining the refractive index changes is
an important method to monitor the deterioration of transformer oil. Oil
deterioration is directly related to the refractive index of transformer oil.
The density of the luminous flux used in the refractive index measurement
changes with the change in the refractive index of the oil. It shows that an
old oil has a higher refractive index than a new oil. As the refractive index
of the oil increases, the breaking stress decreases. Therefore, the refractive
index change will increase or decrease with the level of oil contamination,
which indicates that the oil is new or old.
In this study, the
relationship between refractive index values and diffraction voltage values
of oil samples taken from different high power transformers at different
times was investigated. Previously, the refractive index values of the
samples were measured with an IR280 refractometer. The refractive indices of
the oils varied between 1.4699-1.4820. Then, voltage diffraction tests were
performed on the samples taken with the OTS 60 AF device. The tests started
with the process of heating the oil and reducing the moisture in it and then
the voltage values were increased starting from 0 V up to 60 KV. While the
breakdown voltage of 1.4699 oil was obtained as 60 KV, breakdown voltage of
1.4820 was determined as 26.5 KV. It was seen from the results obtained that
oils with a low refractive index break at higher voltages and become conductive.
The refractive indices of the samples whose refractive indices were measured
before the voltage diffraction test were also measured after the test. Since
the high temperature created by each voltage diffraction test in the oil causes
deterioration in the chemical structure of the oil, a slight increase was
observed in the refractive index values after the test. This clearly reveals
the deterioration of the oil and the change in its chemical structure. The
higher the value of the refractive index of the transformer oil, the lower the
light power losses in the oil sample.