How to monitor gas in transformer oil

Date: January 22, 2026 15:28:50

The core of gas monitoring in transformer oil isDetection of characteristic fault gases dissolved in oil(such as hydrogen H₂, methane CH₄, ethane C₂H₆, ethylene C₂H₄, ethyne C₂H₂, etc.), through the gas components, content and change trend to determine the transformer's internal latent faults (eg, overheating, electrical discharge). Currently, the mainstream monitoring methods are divided intoOffline monitoringrespond in singingOnline monitoringThe two main categories, the specific principles and processes are as follows:

I. Off-line gas chromatography monitoring (traditional laboratory methods)

This is widely used in the power industryPrecision Testing Methods, applicable to periodic preventive testing, the core process is divided into three steps:
  1. oil sample collection

    In accordance with the specification of DL/T 450-2017 Guidelines for Analysis and Judgment of Dissolved Gases in Transformer Oil, oil samples are extracted from the oil drain valve or sampling valve of the transformer body, and air mixing is avoided throughout to ensure the sealing of the oil samples.

  2. oil vapor separation

    adoptionheadspace degassingmaybevacuum degassingSeparates dissolved gases from the oil:

    • Headspace degassing method: the oil sample is put into a closed container, after constant temperature oscillation, the gas in the oil is released to the top space of the container, and the top gas is extracted as the sample to be tested;
    • Vacuum degassing method: use vacuum environment to reduce gas solubility, so that the gas in the oil quickly precipitated, degassing efficiency is higher, suitable for low concentration gas detection.
  3. Gas Chromatography

    Inject the separated gas into theGas ChromatographThe separation of the different gas components is carried out by a chromatographic column, and then the concentration of each component is detected by a detector (e.g., hydrogen flame ionization detector FID, thermal conductivity detector TCD), and a report on the content of the gas components is ultimately generated.

  4. fault diagnosis

    Based on the test results, combined withtrinomial method (math.)The transformer is used to determine whether there are fault types such as overheating, partial discharge, arc discharge, etc. inside the transformer by using criteria such as the characteristic gas method.

vantage: High detection accuracy and comprehensive component identification;drawbacks: No real-time monitoring is possible, there is a lag, and there is a reliance on manual sampling and laboratory analysis.

II. On-line monitoring of dissolved gases in oil (DGA on-line monitoring system)

This is the realization of the transformerstate maintenanceThe core technology of the system can real-time, continuous monitoring of gas changes in the oil, timely warning of failure, the system composition and workflow are as follows:
  1. System Core Components
    • Oil pickup/return unit: Connected to the transformer body through the oil pipe, the oil sample can be continuously circulated or intermittently extracted to ensure the representativeness of the oil sample;
    • In-line degassing unit: Built-in membrane separation degassing module or vacuum degassing module automatically separates gas from oil without manual intervention;
    • sensor unit: The core components are miniature gas chromatographs, infrared spectroscopic sensors or semiconductor sensors with different characteristics for different detection technologies:
      Testing technology vantage drawbacks
      Micro gas chromatography Accurate component identification and wide range High equipment cost and slightly larger size
      infrared spectroscopy Fast response time and easy maintenance Low sensitivity to detect low concentrations of H₂.
      semiconductor sensor method Low cost and small size Susceptible to interference from other gases, average accuracy
    • Data processing and communication unit: Analyze and store the inspection data and upload it to the backend monitoring system via RS485, industrial Ethernet or wireless communication (NB-IoT/5G);
    • Auxiliary units: Contains a temperature control module, a calibration module, and a protective enclosure (adapted to the outdoor environment of a substation).
  2. workflow

    The oil sample flows into the monitoring system from the transformer body → degassing unit separates the gas → detection unit analyzes the gas components and concentration → data unit calculates the gas growth rate and generates the trend curve → automatically triggers an alarm when the standard is exceeded (sound and light, platform push, SMS notification).

vantage: Highly real-time, no human intervention required, captures fault trends;drawbacks: The initial investment is higher than for offline testing, and some of the sensors require periodic calibration.

III. Supplementary: key considerations for gas in oil monitoring

  1. Correspondence between characteristic gases and faults: for example, a large increase in acetylene (C₂H₂) usually corresponds to arc discharge faults, and an increase in ethylene (C₂H₄) is mostly a high temperature overheating fault;
  2. The online monitoring system needs to be regularlyOffline Calibration, ensuring that test data are consistent with laboratory results;
  3. Monitoring data need to be combined with transformer load changes, ambient temperature and other factors to analyze comprehensively to avoid misjudgment.