Effect of magnetic properties of liquid dielectric on the leakage flux of power transformer

The magnetic flux in the transformer establishes the magnetic link between the low voltage and high voltage windings. The magnetic flux chooses the path of lowest reluctance. In general, the transformers are designed such that most of the flux flows through the core. The magnetic flux will experience low reluctance if the medium through which it is flowing is ferromagnetic. The core in transformer is made up of cold rolled grain oriented (CRGO), a ferro-magnetic material to reduce the reluctance to the magnetic flux linkage, to maintain high flux density, to maximize magnetic induction, to minimize specific core loss at no load, and low magnetostriction. Leakage flux is responsible for the voltage dip on the secondary side, hence its reduction is important to maintain good voltage regulation and efficiency. The leakage flux also flows through the liquid dielectric used for insulation and cooling purposes in transformer. The magnetic nature of liquid dielectric is very much important to analyze its impact on leakage flux. For this purpose, two variants of liquid dielectrics, mineral oil (MO), and vegetable oil (VO) are studied for their magnetic nature using vibrating sample magnetometer. The liquid insulation magnetization is plotted with respect to magnetic field strength. The diamagnetic materials repel the magnetic field lines. The VO is found to be more diamagnetic in nature than the MO from the analysis. The influence of the diamagnetic nature of liquid dielectric on the leakage flux, and the advantage of VO over MO in terms of magnetic nature is discussed in this paper and corroborated.