Mineral insulating oils are an important insulating materials in oil-filled transformer, However, the mineral oil is the cause of the environmental problem, The vegetable oils are substitutes for mineral oil because of its biodegradability characteristic, As large size and high rating of the transformer increases, the losses increase at a faster rate, So insulating oil is forced circulation in the oil-filled transformer by using oil pumps. The flow electrification occurs when insulating oil was forced to be circulated. To check the flow electrification, had conducted experiments varying factors. As a result, the streaming electrification could see the changes according to flow velocity, oil temperature and insulation materials.