Online dissolved gas monitoring: combining reliability with affordability
Monitoring the formation of gases in power transformers to detect fault conditions is not new. The Buchholz relay, which responds to the pressure increase produced by fault gases, has been around since 1921, and devices of this type are still in widespread use today. The first objective of online monitoring was to determine the amount of moisture dissolved in oil, but research was underway in the 1970s to develop online dissolved gas analysis (DGA) technologies, initially with a focus on monitoring hydrogen. More recent developments have included ‘fuel-cell’ technology, which allows the detection and measurement of combustible gases in oil.
Limitations of existing fault detectors
Decades ago, the first fault detectors were at the forefront of dissolved gas monitoring and used what were, for the time, innovative technologies. However, over the years some of these technologies have shown weaknesses and shortcomings, either in terms of long-term reliability or in the quality and usefulness of information provided to transformer operators. Alarms in benign situations and missing alarms due to interference from other gasses have driven many users to take the monitors offline or to stop paying close attention to them. On the other hand, multi-gas monitors that detect seven or more gasses are too expensive for widespread deployment, especially on low and medium power transformers. Attempts to fill the middle ground between simple detectors with limited capabilities and sophisticated but costly devices have often met with little success.
Monitoring acetylene and hydrogen to safeguard transformers
The introduction of Megger’s new InsuLogix® G2 online dissolved gas monitor has completely changed this situation. InsuLogix® G2 measures hydrogen and acetylene in addition to moisture in transformer oil. The importance of hydrogen and acetylene as a combination of gasses can be seen in the following chart from IEEE C57.104-2019.
As the chart shows, hydrogen is the predominant gas produced by partial discharge faults in oil, but it is also present as a stray gas. Hydrogen and acetylene are the two predominant gasses formed during high energy electrical faults. At the very beginning of the D1 (low energy discharge) and D2 (high energy discharge) faults, only traces of hydrogen are present, accompanied by low levels of acetylene. As the faults become more aggressive, larger amounts of hydrogen and acetylene are formed due to oil breakdown under high thermal and electrical stress. Monitoring hydrogen and acetylene as key gasses in a two-gas fault detector helps the transformer operator to better understand if the presence of hydrogen in oil is due to possible partial discharge, or as a stray gas, or as a result of high energy electrical discharges. Moreover, the ability to detect acetylene at very low levels allows the transformer operator to identify the high energy faults very early in their evolution.
InsuLogix® G2 for online dissolved gas monitoring
To measure low levels of acetylene gas concentration, the Megger InsuLogix® G2 uses a tuneable laser diode spectroscope (TLDS) sensor, which passes a laser beam through the gas and determines the amount of light absorbed using infrared technology. Since different gases absorb light at different wavelengths, accurate measurements can be made for one specific gas while ignoring other (interfering) gases that may be present. In the InsuLogix® G2, the sensor is tuned for the detection of acetylene, with a sensitivity (LDL) of 0.5 ppm. The InsuLogix® G2 also accurately measures hydrogen and water vapour to help provide comprehensive fault detection.
The Megger InsuLogix® G2 has been designed for ease of installation and use. It has been engineered to operate in all atmospheric conditions (IP66) as well as in the electromagnetic environment found in an electrical substation.
An integral display provides local access to acetylene, moisture, hydrogen, and temperature measurements, while the web-based user interface provides secure remote access to current data as well as historical measurements and trends. Measurements can be presented as an intuitive dashboard-type display. The unit also has 12 customisable solid-state relay outputs that can be configured to provide warnings and alarms.
Megger’s InsuLogix® G2 is an advanced fault detector positioned between hydrogen, hydrogen plus carbon monoxide, composite gas monitors, and the diagnostic/Duval 3+ gas monitors. By accurately detecting low levels of acetylene using state-of-the-art laser spectroscopy technology, the InsuLogix® G2 increases situational awareness, allowing transformer operators to make informed decisions.
The design of the InsuLogix® G2, the combination of gases it detects, its ease of installation and cost-effectiveness make it an ideal solution for widespread deployment across medium power transformers in all types of applications. As the power industry continues to evolve and the demand for reliable, affordable monitoring technologies grows, the InsuLogix® G2 helps safeguard the longevity and performance of transformers.
If you require additional technical materials, product guidance, or support please contact Megger.
