In determining the type of fault with a transformer, Gas Ratio Codes have been developed. The relative amounts of various gases change as the fault pattern changes. There are certain "key" gases that point to a particular type of fault within a transformer. For example: 

KEY GAS	FAULT
Ethylene (C2H4) / Ethane (C2H6) / Methane (CH4)	Severe oil overheating/hot spots
Hydrogen (H2)	Partial discharge, "Corona"
Acetylene (C2H2)	Arcing

The levels of concern for the following gases as determined by the IEEE, Bureau of Standards and Dornenburg are listed below: 

GAS (PPM)	IEEE	BUREAU OF STANDARDS	DORNENBURG
Acetylene	11	7	5
Carbon Dioxide	580	10000	6000
Ethane	115	75	35
Ethylene	190	175	80
Hydrogen	240	500	200
Methane	160	125	50

Currently, the most accurate way of determining the type and concentration of gas present in a transformer is to perform a Dissolved Gas Analysis (DGA). A DGA is performed by extracting a sample of the transformer oil and sending it to a testing laboratory. The dissolved gas is removed from the oil and analyzed in a gas chromatograph specific for transformer oil. The data provided by the gas chromatograph helps to determine the condition of the transformer and serves as a guide for continued transformer operation. 

Performing a DGA on transformers costs time and money. There is the time spent to extract the oil sample, time to send the sample to a testing laboratory and the cost of analysis. To reduce the cost and time required to determine the health of a transformer, the portable Innova-XT (Transformer Gas Tester) can be used to test for the presence of combustible gas in the headspace of many transformers. The Innova-XT is specifically designed to meet this unique application and provides real-time feedback. The information from the Tester is used to determine if transformer faults exist or if a dissolved gas analysis is required. 

SIMPLE TESTING PROCEDURE: 

Fill the three-liter Tedlar bag with a gas sample from the headspace of the transformer, and then connect the bag to the Innova-XT(Transformer Gas Tester). If combustible gas is present, the GT Transformer Gas Tester displays readings in either the ppm or percent LEL ranges. 

INTERPRETATION OF THE RESULTS: 

The gas readings will be in total combustibles. If the total combustibles exceed a level of 500 ppm for example, or if readings increase on an abnormal basis, then further investigation of the transformer is advised. 

As stated by L.E. Luke, "Gas Detection, a Key to Transformer Health," Westinghouse Corp., January 1980, "Levels of hydrocarbons from 0-500 ppm represent normal aging of the transformer. Analyze again in six months. Levels from 501-1200 ppm indicate that decomposition may be in excess of normal aging. Analyze again in three months. Levels from 1201 to 2500 ppm indicate more than normal decomposition. Analyze again in one month. Levels from 2501 and up, make weekly analysis to determine rate of generation. A rate of increase in combustible gas generation of 100 ppm or more for a 24 hour period, on a continuing basis, with a relatively constant load, indicates a deteriorating condition and requires that an assessment be made regarding operation." 

SUMMARY: 

Thermo Scientific's Innova-XT (Transformer Gas Tester) can be a valuable and time saving tool to monitor for the presence of combustible gas in transformer headspaces. This quick test can then be used to determine if extensive analysis is required. Depending on the frequency of performing dissolved gas analysis, the return on investment (ROI) on the Innova-XT may be in just a few months.