Megger InsuLogix® G2 Application Note
1 / 5Pages

Application Note Online Dissolved Gas Analysis with Megger InsuLogix® G2 Accurately measuring low levels of acetylene dissolved in insulating fluid (oil) in the presence of ‘interfering gases’ is vital for promptly identifying critical arcing faults in power transformers. Online dissolved gas analysis (DGA) monitors with this ability have historically been too costly to allow largescale, fleet-wide deployment. This application note describes a new solution – the Megger InsuLogix® G2 – which provides accurate measurement of acetylene in oil, in addition to measuring hydrogen as an early fault indicator, at a price point that justifies its deployment on medium and large power transformers. Background Monitoring fault gases in transformers has a long history, dating back to the introduction of the Buchholz relay in 1921, which essentially responds to an increase in pressure as the fault gases are produced. A significant step forward was the introduction of online DGA in the 1970s, initially for assessing the level of moisture in the oil. While moisture is not a fault gas, its increased presence is likely to negatively impact the life of the transformer. Soon after, DGA technology was extended to allow the level of hydrogen (H2) in the oil to be monitored. This was a major step forward as active fault conditions could now be detected in near-real-time at their incipient stage by measuring the concentration of a specific combustible gas. Megger limited Archcliffe Rd, Dover Kent, CT17 9EN United Kingdom Registered No. 190137 Registered to ISO:9001:2008 Certificate No.

Application Note In the late 1970s, online measurement of gases in oil using ‘fuel cell’ technology was introduced. With four combustible gasses detected in various percentages of their true concentrations, the technology remains popular today. It provides coarse detection of incipient faults, but it cannot discriminate between critical arcing faults and low energy faults. Also popular for the past two decades has been hydrogen with moisture sensors. These can be used to implement a relatively simple, low-cost warning/alarm solution that provides a first level response to incipient faults,...

Application Note Figure 2: Relative dissolved gas concentrations in mineral oil versus fault types As this diagram shows, hydrogen and acetylene (C2H2) are the two key gases that need to be monitored to provide a high level of protection for a transformer. As the fault begins to develop, hydrogen is typically the most prevalent gas generated. However, acetylene gas development levels of greater than 2 ppm and increasing, indicate a critical arcing fault that would be easily missed if only hydrogen were monitored. By combining two strategies – incipient fault detection based on hydrogen...

Application Note Interfering gases and compounds in transformer oil include, but are not limited to, hydrogen, water, ethane, methane, ethylene, carbon monoxide, carbon dioxide and heavy compounds such as alcohols, ketones and aldehydes. When it is necessary to measure small concentrations of a target gas such as acetylene, the interfering gases and compounds contribute significantly to measurement errors when conventional technologies are used. With its inherent selectivity, the TDLS system used in the InsuLogix® G2 provides an effective solution to this problem at an economical price. The...

Application Note Figure 3: Example of a dashboard display for InsuLogix® G2 Megger limited Archcliffe Rd, Dover Kent, CT17 9EN United Kingdom Registered No. 190137 Registered to ISO:9001:2008 Certificate No. Q 09250