Dissolved Gas Analyzer

The dissolved gas analyzer is one of the most widely recognized and essential methods for diagnosing and monitoring the operational condition of power transformers. This diagnostic tool is primarily used to analyze dissolved gases and moisture content of transformer oil, providing valuable insight into the proper functionality and long-term performance of transformer equipment. It is commonly applied to industrial power transformers rated at 110 kV and above, as well as to unit transformers and high-voltage sealed bushings up to 110 kV that are filled with transformer oil.

Role of Dissolved Gases in Transformer Oil

New transformer oil is initially free of dissolved gases. However, as the transformer operates, various gases begin to develop within the oil over time. Each gas is associated with specific types of internal faults. By measuring gas concentrations and tracking their rate of increase, it is possible to identify emerging transformer defects and predict their progression with a high degree of certainty — in some cases up to 95%.

The main gases present in transformer oil include:

• Hydrogen (H₂): indicates electrical faults, such as low-energy partial discharges, sparkovers, or hot spots.
• Acetylene (C₂H₂): develops during high-energy discharges (sparking, arcing), typically at temperatures exceeding 1,292 °F.
• Methane (CH₄): results from oil and insulation overheating (482°F to 752°F) due to transformer overloads, cooling system defects, or low-energy partial discharges.
• Ethane (C₂H₆): indicates thermal heating of oil and paper-oil insulation at temperatures above 572 °F.
• Ethylene (C₂H₄): develops due to high-temperature heating of oil and paper-oil insulation, reaching the temperatures over 1,112 °F.
• Carbon Monoxide (CO): associated with aging and moisture contamination of oil or solid insulation and overheating of insulation throughout the system.
• Carbon Dioxide (CO₂): indicates aging and overheating of solid insulation, such as paper and pressboard.

Importance of Gas Chromatography

Gas chromatography (GC) is the primary method used for dissolved gas analysis of transformer oil, which is typically performed every six months. This technique helps you detect the faults mentioned above, track their development, and anticipate potential issues that may not be identifiable with the use of conventional non-destructive testing methods.

However, one limitation of GC is its inability to detect rapidly developing defects, such as arc bridging, turn-to-turn short circuits, creeping discharges, and sudden insulation breakdowns. In addition, the GC process requires specialized laboratory equipment and skilled industrial chemists, which makes it impractical for field use in many cases.

Dissolved gas analyzer: a field solution

In order to address this limitation, Fluidex recommends the use of a portable dissolved gas analyzer. This device enables rapid and efficient testing of transformer oil directly in the field, allowing users to assess oil condition and suitability for continued operation within minutes. As a result, this portable solution provides a practical alternative to laboratory-based analysis and is well suited for on-site diagnostic evaluation.

Types of dissolved gas analyzers

Dissolved gas analyzers are classified into several types based on their portability and intended application. These include:

1. Portable Gas Analyzers: these compact and easily transportable devices are designed for use in a wide range of environments. Most portable analyzers are equipped with digital displays to present measured parameters and with alarm systems to alert users when gas concentrations exceed preset thresholds. They are primarily used for air quality monitoring in confined spaces, such as underground facilities.
2. Semi-Portable Gas Analyzers: these devices are slightly larger than portable analyzers, but offer improved functionality and enhanced reliability. Semi-portable analyzers are commonly used by industrial companies to detect concentrations of toxic and combustible gases in the air.
3. Fixed-Type Gas Analyzers: permanently installed systems that require high reliability, accuracy, and fast response times. These analyzers are typically equipped with both visual and audible alarms and support data transmission via modern communication channels, such as the Internet, enabling remote monitoring and analysis on a personal computer.

While gas chromatography offers accurate and reliable results, portable gas analyzers provide a practical solution for on-site testing. Whether used in mobile, semi-portable, or fixed configurations, gas analyzers help you ensure the safe and efficient operation of critical transformer equipment, contributing to enhanced reliability and improved overall performance.