37 / 2018-08-13 14:24:06

A Novel Three-Element Mixed Insulation Oil and Its Application in 10kV Distribution Transformer

mixed insulation oil,,distribution transformer, insulation property, thermal property

The main insulation system of a power transformer consists of a cellulosic material and insulation oil. Mineral oil has been used in power transformers for more than 100 years. Extensive research has been conducted on mineral oil substitutes in many countries due to the requirements of green energy and environmental protection. Natural esters are good substitutes for mineral oil. They present fire safety, environmental, and insulation ageing advantages over mineral oil. However, natural esters possess high viscosity, high dielectric loss, high acidity, and poor oxidation stability, and these properties require changing the structural design of transformers. Many studies have been conducted on mixed insulation oil in recent years. This kind of oil demonstrated advantages in delaying the aging rate of insulation paper. However, the parameters of these mixed insulation oils cannot meet the requirement of the IEC 60296:2012 standard.
Since 2017, our team has been planning to develop a new type of mixed insulation oil on the basis of previous research. The parameters of this oil would satisfy the IEC 60296:2012 requirement, and the proposed oil would exhibit better breakdown and permittivity performance than traditional mineral oil and better viscosity, dissipation factor, acidity, and oxidation stability than natural esters. This new type of mixed insulation oil could be used without changing the structural design of the original transformer.
In this paper, a novel three-element mixed insulation oil was introduced, and its application in 10kV distribution transformer was investigated. The main parameters of the novel three-element mixed insulation oil (76 v.% mineral oil + 19 v.% soybean oil + 5 v.% PFAE oil + 0.2 wt% T511 + 0.2 wt% L06) meet the IEC standard (60296:2012) for mineral oil. The mixed oil has higher oxidation stability than mineral oil and lower viscosity, dielectric loss, and acidity than natural esters. The novel three-element mixed insulation oil has a similar kinematic viscosity as mineral oil. The thermodynamic properties of the novel three-element mixed insulation oil are superior to those of mineral oil. Its specific heat capacity and thermal conductivity values are higher than those of mineral oil between 30 °C and 100 °C. The saturated water content of the novel three-element mixed insulation oil is approximately 3–4 times larger than that of mineral oil above 45 °C. The mixed insulation oil has a higher AC breakdown voltage than mineral oil under the same absolute water content.
In this research, without changing the insulation structure of the transformer, an old mineral oil distribution transformer (SBH15-M-400/10-0.4) serviced for 8 years was filled by the novel three element mixed insulation oil. In addition, a new distribution transformer (s11-M-400/10-0.4) was also filled by the novel three element mixed insulation oil. All the parameters of the both distribution transformer above meet the requirement of the standard. Compared with the same distribution transformer filled by mew mineral oil, the distribution transformer filled by the novel three-element mixed insulation oil has good insulation resistance, DC resistance, dielectric loss, no-load and load loss, etc. The good performance of the novel three-element mixed insulation oil ensures the safe operation of the old and new 10kV distribution transformer.