Yasunori Hatta

Analyses of electro-chemical characteristics of Palm Fatty Acid Esters as insulating oil

We have developed a new vegetable based insulating oil for transformers called PFAE (palm fatty acid ester). PFAE has 0.6 times less viscosity and a 1.3 times higher dielectric constant compared to mineral oil. This means that a PFAE-immersed transformer has better cooling efficiency and better insulation characteristics in paper-and-oil composite insulation systems, resulting in size reduction in comparison to conventional transformers immersed in mineral oil. Additionally, the flash point of PFAE is higher than that of mineral oil. PFAE also shows higher biodegradability when compared to mineral oil. PFAE would be much safer for the environment than mineral oil in the event of soil or water contamination. Moreover, electrical insulating oil in transformers used over several decades requires excellent durability. The oxidative stability of PFAE has also been determined to be superior to mineral oil.

Space charge behavior in palm oil fatty acid ester (PFAE) by electro-optic field measurement

For power transformer insulating oil, we focused on palm oil fatty acid ester (PFAE). It has satisfactory insulating performance, excellent cooling ability and superior biodegradability. Recently, investigations for application of PFAE to environment-friendly power transformers installations have been started. In this paper, the space charge behavior in PFAE was investigated from the measurement results of the electric field by using Kerr electro-optic method under dc voltages applications. For the field measurement, the Kerr constant of PFAE was identified first. Then, the electric field strength and its temporal change were measured in several PFAE / pressboard (PB) insulation systems. The electric field in PFAE was determined by the capacitive distribution at the moment of the voltage application, and decreased rapidly with time and reached the steady state determined by the resistive distribution. The transition time of the capacitive distribution to the resistive one and the strength of electric field in PFAE were much different from those in mineral oil. The influence of oil flow on the time transition of the electric field was also measured. Their differences were discussed with the charge behavior in liquids, based on electro-chemical properties of the oil. We discussed the difference of the flow electrification characteristics between PFAE and mineral oil, and its mechanism was discussed based on the charge behavior in oils.

Fundamental property of electric field in rapeseed ester oil based on Kerr electro-optic measurement

In the future, environmentally friendly insulating oil such as rapeseed ester oil is expected to be utilized as a substitute for mineral oil for power transformers. In addition, electrical insulation design for transformers becomes more important regarding size reduction and enhancement of electric field stress. The fundamental property of the electric field distribution in the rapeseed ester oil and in the oil/solid dielectrics composite insulation system should be clarified. In this paper, we have directly measured the electric field in the rapeseed ester oil with parallel-plane electrode and the rapeseed ester oil/pressboard (PB) composite insulation systems under DC voltage application using the Kerr electro-optic technique. From the results, we compared measurements of electric field and charge behavior for the rapeseed ester oil and the mineral oil and confirmed the applicability of the rapeseed ester oil for use in transformers

Kerr electro-optic field measurement in palm oil fatty acid ester transformer insulation system

A palm oil fatty acid ester (PFAE) has good insulation performance, excellent cooling ability and superior biodegradability. Recently, investigations for application of PFAE to power transformers have been started. In this paper, the electric field in PFAE was measured in situ by using Kerr electro-optic method under dc voltages application. At first, Ken-constant of PFAE was identified. Then, electric field strength E and its temporal change were measured in several PFAE / pressboard (PB) insulation systems. Electric field E in PFAE showed the capacitive distribution at the moment of dc voltage application, and decreased rapidly with time and finally the resistive field distribution was obtained. The transition time of the capacitive distribution to the resistive one and the value of E in PFAE were different from those in mineral oil. Their differences were discussed with the charge behavior in liquids, based on electro-chemical properties of the oil.

Charge behavior in Palm Fatty Acid Ester oil (PFAE) / pressboard insulation system under flow condition in power transformers

From viewpoints of low environment impact, palm fatty acid ester oil (PFAE) is potent insulating liquid for power transformers because of its high biodegradation performance. Moreover, PFAE has high permittivity, low viscosity, high thermal and chemical stability and high productivity. These characteristics well satisfy the requirement of electric insulation performance in power transformers. In this paper, electric field distribution in a PFAE / pressboard insulation system was measured with a Kerr electro-optic technique at various oil flow conditions under dc voltages and the charge behavior was investigated systematically. We discussed the difference of the flow electrification characteristics between PFAE and mineral oil, and its mechanism was discussed based on the charge behavior in oils.

Impulse creeping discharge characteristics in insulating oils with EHD function reinforced by added HFC gas components

This paper describes the results obtained from the study on EHD pumping and dielectric strength in two oils, rape-seed ester oil and silicone oil, denatured by slightly added HFC134a gas components. It is shown that the insulation ability of denatured oils drops compared to that of standard oils, but the EHD pumping is reinforced significantly by the creation of bonding such as C-F and C-H in HFC gas. This EHD function may be utilized as a new cooling method in oil-filled power apparatuses in view of the dielectric strength.