Recently, Guangzhou Power Supply Bureau of Guangdong Power Grid Co., Ltd. announced that the world’s first 500kV vegetable oil transformer has been successfully put into operation at one of the 500kV Substations in Guangzhou. As the vegetable oil transformer with the highest operating voltage level across the globe to date, this landmark equipment realizes China’s leap from following to leading in the field of high-voltage environment-friendly transformers, and fills the international gap in the practical application of 500kV natural ester insulating oil transformers.

The transformer is filled with approximately 65 tons of natural ester insulating oil, and fitted with intelligent devices including a fully automatic on-line oil chromatography monitoring system, enabling 24-hour real-time condition monitoring and intelligent control for energy-saving operation.

Compared with traditional mineral oil transformers, vegetable oil transformers have prominent environmental advantages of zero pollution and high reliability. Given their superior environmental and reliability performance, why is it still essential to equip such transformers with intelligent monitoring equipment including the transformer Dissolved Gas Analysis (DGA) on-line monitoring device?

1. DGA Remains the Core Means for Fault Diagnosis of Vegetable Oil Transformers

Despite the excellent environmental performance of vegetable oil (natural ester) insulating oil, transformers may still generate characteristic gases including hydrogen (H₂), methane (CH₄), acetylene (C₂H₂), carbon monoxide (CO) and carbon dioxide (CO₂) during operation due to faults such as overheating and discharge. By monitoring the concentration and gas generation rate of these gases, DGA technology can detect potential faults including partial discharge, electric arc and overheating at an early stage. Its critical importance will not be reduced by the change of insulating oil type. On the contrary, the higher the voltage level, the more necessary the transformer DGA monitoring is.

In addition, vegetable oil has poor compatibility with traditional materials used in transformers (such as seals and paints), and may corrode transformer accessory materials, resulting in the generation of gases such as CO and CO₂. Therefore, DGA monitoring of these gases is particularly vital for the safe operation of vegetable oil transformers.

2. Particularity of DGA Monitoring for Vegetable Oil

Different from mineral oil (hydrocarbons), the focus of monitoring shall be adjusted accordingly for vegetable oil. Vegetable oil (esters) has significant differences in gas generation characteristics under fault conditions: it is more prone to generate CO and CO₂, and the content of C₂H₂ is usually low, while its occurrence often indicates that the discharge fault has been relatively serious. By contrast, mineral oil mainly generates hydrocarbon gases such as methane (CH₄), ethane (C₂H₆) and ethylene (C₂H₄) in case of faults, which carry high flammable and explosive risks.

3. Key Gases for DGA Monitoring of Vegetable Oil Transformers

DGA monitoring for vegetable oil transformers requires close attention to key gases including H₂, CH₄, C₂H₄, C₂H₂, CO and CO₂. Among them, CO and CO₂ may be produced in large quantities during the oxidation or thermal degradation of vegetable oil, which need to be monitored closely. Meanwhile, oxygen (O₂) and micro-water (H₂O) shall also be focused on, as vegetable oil is susceptible to moisture absorption and oxidation. Comprehensive judgment shall be made in combination with oil quality indicators such as acid value and water content.

4. Application Recommendations for DGA Monitoring of Vegetable Oil Transformers

• Configure high-precision on-line DGA monitoring devices: For example, the high-precision and high-reliability photoacoustic spectroscopy on-line monitoring and early warning device for transformer oil and gas developed by Hubei Infotech System Technology Co., Ltd., which can realize real-time monitoring of full-component gases and micro-water, and enhance fault early warning capability.
• Establish exclusive DGA baseline data for vegetable oil: Due to the limited monitoring experience of vegetable oil transformers, it is necessary to accumulate long-term operation data to establish the gas reference value under normal operating conditions.
• Adopt special criterion standards for vegetable oil: Avoid misjudgment caused by applying mineral oil standards, and carry out comprehensive diagnosis combined with multi-dimensional data such as electrical tests and oil laboratory tests.

While vegetable oil transformers have inherent environmental advantages, their operating status still relies on on-line DGA monitoring to guarantee operational safety. Ignoring DGA monitoring may lead to insulation degradation and even equipment damage. Therefore, even the newly launched, more environment-friendly 500kV vegetable oil transformer needs to be equipped with advanced intelligent monitoring systems to ensure its long-term stable operation.