What is the breakdown voltage of vegetable oil?
There's actually an extensive research done on vegetable oil, especially on breakdown voltage. The commonly used term to refer vegetable oil in the field of transformer liquid insulation is "natural ester". Japan has used palm oil in some of their transformers since year 2000s. In a paper I read, the breakdown voltage of palm oil (olein) is between 44-60 kV (reference: "Suitability of Palm Based Oil as Dielectric Insulating Fluid in Transformers" by Azis, Norhafiz; Jasni, Jasronita; Ab Kadir, Mohd Zainal Abidin ;Mohtar, Mohd Nazim).