Technical Articles

Monitoring Technology of Dissolved Hydrogen in Transformer Oil

 Monitoring Technology of Dissolved Hydrogen in Transformer Oil

DGA HYDROGEN MONITORING


Introduction
The Asia Pacific dissolved gas analyzers (DGA) market is expected to reach USD 1.11 billion by 2024, expanding at a CAGR (Compound Annual Growth Rate) exceeding 12.0% over the forecast period, according to Grand View Research [1]. This growth is based on mitigating faults in high-voltage transformers combined with the high cost of transformer replacement. Incorporating real time DGA analytics aids companies in detecting faults in power transformers at the onset instead of weeks or months later. Early diagnosis allows clients to develop proactive maintenance programs to avert faults and extend the life of power transformers. This is expected to propel global demand for online DGA systems significantly over the next few years. Figure 1 illustrates this trend specific to Asia Pacific.

Background
China's electric power industry has rapidly developed with the accelerated development of China's economy and associated science & technology. This economic development has improved the quality of life by propelling forward increased requirements for the operation, reliability, and life of their power system equipment. To this end, analyzing dissolved gases in transformer oil is the most effective method of evaluating the operation of oil-filled transformers. Online monitoring devices that measure dissolved gas in transformer oil are vital tools for the power industry's operation and maintenance management of critical equipment.




Figure1 500

Figure 1. Asia Pacific Dissolved Gas Analyzer Market by extraction type, 2013 - 2024 (USD Million) (Source: Grand View Research [1])

Hydrogen is one of the key gases reflecting the internal insulation defects of fluid-filled equipment. Monitoring hydrogen in transformer fluid has several advantages including small size, convenient installation, and rapid response to sudden failures. In recent years China’s DGA programs have been standardized and applied in monitoring both in-service and newly installed large power transformers to mitigate the risk associated with loss of these important assets.
Hydrogen Sensor Application
A Hydrogen sensor is a device that detects hydrogen and generates an electrical signal proportional to the Hydrogen concentration. Compared with traditional gas chromatograph or mass spectrometer detection, solid state Hydrogen sensors provide the advantages of low cost, small size, fast response, no maintenance, no cross-sensitivity, long life and online real-time monitoring.
Technical Principles of Transformer Oil Decomposition:
Transformer oil is a mixture of various hydrocarbon molecules of different molecular weights. Electrical or thermal failure can break certain C- H bonds and C- C bonds, accompanied by the generation of a small number of active Hydrogen atoms and unstable hydrocarbon radicals (China State Grid Research Center). These Hydrogen atoms or radicals rapidly recombine through complex chemical reactions to form hydrogen.
Technical Core Performance Indicators Include:
  1. Detection range and measurement accuracy
  2. Minimum detection concentration
  3. Minimum sampling interval time
  4. Measurement repeatability
  5. Response Time (T90)
  6. Cross sensitivity

DGA hydrogen monitoring in transformer oil has the advantages of small size, convenient installation, and rapid response to sudden failures.

Table1 950
Table 1. Technical Standards and the Application of Hydrogen Diagnosis in Oil (PPM Level) (Source: China State Grid Research Center [2])


Per China State Grid Corporation Standard Q/GDW 10536-2021, the measurement range for monitors should meet the requirements outlined in Tables 2, 3 and 4.

Measurement accuracy performance is rated in Classes A, B, C: Table 2 for 750 kV and above sub-station device requirements; Table 3 for 500 kV Substation device requirements; Table 4 for Lower voltage device requirements.

Table2 950
Table 2. Measurement requirements for multi gas monitors in substations of 750 KV and above. Standard Q/GDW 10536-2021 (Source: China State Grid Research Center [3])

Table3 950

Table 3. Measurement requirements for multi gas monitors in substations of 500 KV and below. Standard Q/GDW 10536-2021 (Source: China State Grid Research Center [3])

Table4 950

Table 4. Measurement Requirements for few gas monitors Table 3. Standard Q/GDW 10536-2021 (Source: China State Grid Research Center [3])

Commonly Used Devices
Monitoring devices for dissolved hydrogen in transformer oil include a dissolved hydrogen sensor, control and data acquisition equipment, communication and auxiliary modules, and an installation interface.
Installation Simulation Tests and Setup Examples include:
  1. Gas relay gas collection alarm testing
  2. 100°C oil temperature continuous power-on assessment
  3. Simulation test for retrofitting a single hydrogen monitoring device
  4. Joint pipe installation monitoring device vibration; vibration stress test
In-plant Installation and Verification
Chinese Academy of Electrical Sciences has installed a hydrogen monitoring device on a large power transformer and ran feasibility analysis. Physical testing takes place once the performance verification and simulation operation tests have been carried out.

Compared with traditional hydrogen gas chromatograph or mass spectrometer detection, hydrogen gas sensor provides advantages of low cost, small size, fast response, no maintenance, no cross-sensitivity, and online real-time monitoring.

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Conclusion
In summary, the application of online monitoring ensures the stability of the transformer, saves high labor costs, reduces the frequency of sampling and improves efficiency. Ongoing improvement in the industry requires suppliers, operators and technicians to conduct in-depth research and continuous improvement based on problems arising in the industry. The sector strives to provide the most reliable data for transformer monitoring to allow for the power grid's optimized function for everyone's benefit.

References
  1. “Dissolved Gas Analyzer Market Size, Share & Trends Analysis Report By Extraction Type (Vacuum Extraction, Headspace Extraction, Striper Column Method), By Power Rating (100-500 MVA, 501-800 MVA, 801-1200 MVA), By Analysis Type and Segment Forecasts To 2024,” Grand View Research, accessed at https://www.grandviewresearch.com/industry-analysis/dissolved-gas-analyzer-dga-market
  2. “Monitoring Technology for Dissolved Hydrogen in Transformer Oil,” China State Grid Research Center, accessed at https://edirc.repec.org/
  3. “Standard Q/GDW 10536-2021,” China State Grid Corporation


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Julie Feng obtained her degree in mechanical engineering from China Shanxi Technology University in 2008. Over the past ten years Julie has been engaged in industrial sales, working with the largest DGA OEMs in China, supporting the State Grid and other private entities. Julie is currently Business Development Director at H2Scan, China.
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