Electro-mechanical testing of a liquid nitrogen filled power transformer

To remove the environmental and safety hazards associated with power transformers, the authors have investigated the use of liquid nitrogen as a replacement for transformer oil. This paper details tests performed to determine new design rules and efficiency expectations of liquid nitrogen filled power transformers (Enviro-Transformers). The tests include dielectric strength testing of liquid nitrogen and mechanical strength testing of standard transformer insulating materials submerged in liquid nitrogen. Efficiency and dissipation factor tests were performed on two industry standard 10 kVA, 50 Hz, 11/0.24 kV single-phase transformers. One transformer was filled with oil and operated at room temperature, the other was filled with liquid nitrogen and operated at 77 oK