The invention concerns an electrostatic coalescing device that includes a vessel or a pipe through which a mixture of fluids flows. At least one metal electrode plate and transformer are arranged inside the pipe/vessel. The electrode plate and transformer are fully enclosed by insulation, and the transformer is energized from an external alternating low voltage source/power supply located outside the vessel/pipe. The transformer includes a first end of a high voltage winding connected electrically to the metal plate within the insulation.