Application of the cut-off resonator for microwave monitoring of transformer oil

This paper describes a cut-off resonator designed for testing transformer oil is proposed.The two kinds of transformer oil have been comparedâ" fresh" (unused) and "old" (used) for a long period in real-world conditions. The experimental setup has been designed and assembled on the basis of the cut-off resonator with plastic tube containing the tested oil. There was observed the shift of resonance curves of the measured insertion losses between the "old" and the "fresh" samples. Also, the "old" oil has higher insertion loss that is caused by increasing its loss tangent compared with the "fresh" oil. These parameters can be used for estimating quality of the transformer oils.