Dielectric properties of natural ester, synthetic ester midel 7131 and mineral oil diala D

Abstract

The insulating liquids used in industrial applications are typically mineral oils. In recent years however, significant attention has been paid to alternative insulating fluids, including synthetic and natural ester liquids. In order to expand their practical applications, it is important to have detailed information on their dielectric properties. In this present paper, the dielectric properties of synthetic ester, Midel 7131; mineral oil, Shell Diala D; and vegetable (rapeseed) oil have been investigated. It has been shown that Midel 7131 has a higher ac breakdown voltage (27.6 kV) as compared with Diala D oil (26.4 kV) and rapeseed oil (24.6 kV). However, the breakdown voltage of the Diala D oil has the smallest standard deviation (7%) amongst the tested liquids (13% for Midel 7131 and 11% for rapeseed oil). Statistical analysis of the breakdown voltages has been conducted and it has been shown that the ac breakdown voltages can be described by a normal distribution. dc I-V characteristics have been measured and the space charge saturation regime has been observed for all three liquids starting from ∼9 kV for positive energisation and ∼10 kV for negative energisation in the point-plane topology. Apparent mobilities of the charge carriers in the tested liquids have been obtained using I 1/2 -V curves; these mobilities can be used for calculation of the space charge influenced distribution of the electric field in liquid insulators stressed with dc voltage. Such analysis can be important for design and exploitation of HVDC power systems.

Study of the charge dynamics in mineral oil under a non-homogeneous field

“…As seen from Figures 5-7, the fresh oil has the lowest dielectric loss, the lightly aged oil has a medium dielectric loss and the heavily aged oil has the highest dielectric loss. The dielectric loss of the mineral oil increases with aging [1][2][3][4][5][6][7][8]. As the conductivity of mineral oil also increases with the temperature, the curves of the imaginary part of the complex permittivity shift towards high frequency when the temperature increases.…”

“…Various diagnostic methods have been applied to monitor dielectric changes in insulating liquid over time, no matter these changes are due to thermal, electrical or chemical effects [1][2][3][4]. Dielectric spectroscopy technique, which enables us to gain a bunch of information about the dynamics of bound and mobile charge carriers, has been widely employed in the evaluation of insulating properties of dielectric liquids [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18].…”

Breakdown Voltage Characteristic Of Mineral Oil In Power Transformer 16 Mva Updl Semarang

“…Therefore, if the power transformer oil fails to perform its function as an insulating medium or cooling medium, it can cause damage to the power transformer so that the distribution of electric power to consumers is disrupted [3]. Nowadays, there is a lot of research on liquid isolation to knowing the quality of isolation, isolation eligibility, and find the newest isolation materials [4][5] [6]. Some studies do the breakdown voltage test to knowing the liquid isolation eligibility that has been used for a while, the breakdown voltage test that doing continuously is not widely doing yet.…”

Analysis of High-Frequency Dispersion Characteristics of Capacitance and Loss Factor of Aramid Paper Impregnated with Various Dielectric Liquids

“…Another action, which should be taken mainly by the users of such equipment, is proper operation supplemented with monitoring of the key apparatus of the system. In the case of power transformers, solid and liquid insulation, which so far has been made of cellulose impregnated with mineral insulating oil will be more often substituted with synthetic insulation, mostly made of aramid papers ultimately impregnated with environment-friendly synthetic and natural esters [1][2][3][4][5][6]. Compared with cellulose, the application of aramids causes a significant increase in the resistance to high temperatures, which is presently the main factor having influence on premature aging of insulation [2,[6][7][8].…”

“…The process of departing from using only mineral oils in favor of more ecological synthetic and natural esters can already be observed, even in the case of classical cellulose insulation in new power transformers [13,14]. Such a situation is imposed on one hand by more and more restrictive provisions pertaining to natural environment protection and the reduction of the use of petroleum products and on the other hand better electrical and physicochemical parameters of new esters [3,4,15,16]. Unfortunately, their higher price and lack of wide expert knowledge that science has in the case of mineral oils resulting from years of being in use constitutes a barrier limiting the use of these insulating liquids.…”