Dissolved Gas Analysis Bryan Harbuck May 2017

DGA: WHAT and WHY DGA is the study of the dissolved gases in transformer oil generated by normal operation and fault conditions. As the equipment operates it will create gases within the oil that can be analyzed to determine the “Health” of the equipment. Involves the use of a syringe and bottle. It is used as a predictive maintenance tool and as a monitoring point. DGA gives us a picture of what is going on inside the equipment without having to actually go inside or de-energize it. Careful analysis combined with trending of data can predict at what stage of life your equipment is at.

Gases We Are looking For: Not all gases that are created are used in the analysis. What we are concerned with are the seven “Heating” Gases. These are the gases created by an overheating or fault condition. Each gas has its own signature temperature and tells a story. Gases we are concerned with: Hydrogen, Carbon Monoxide, Carbon Dioxide, Methane, Ethane, Ethylene, and Acetylene. Let have a look at these and see what they are caused by.

Heating Gas Characteristics Temp Formed At: Solubility in Oil (How fast it dissipates) Primary Causes Hydrogen (H2) > 110 C 7.0 % Quickly Partial Discharge (Corona) Carbon Monoxide (CO) > 300 C 9.0 % Quickly Overheated Cellulose Methane (CH4) 30.0 % Moderate Overheated Oil Carbon Dioxide (CO2) > 400 C 120.0 % Slowly Ethane (C2H6) > 150 C 280.0 % Very Slowly Ethylene (C2H4) Overheated Oil (Hotspot) (Sparking) Acetylene (C2H2) > 700 C 400.0 % Extremely Slowly Arcing/Burning Contacts

Oil Quality Tests Dielectric Test: Determines the breakdown point of the oil. Commonly used are ASTM D 1816 and D 877 Test.

Color, Acidity, and Moisture Color: Indication of the oxidation of the oil. As oil ages and oxides it will get darker in color. New oil should be a 0.5 and will get darker with age. Acidity : Another indication of the oxidation of the oil. Will start with a very low number (.01 for new oil and rise as oil degrades) Moisture: Karl Fischer Test is used. Moisture can come from 2 sources: Leaking gaskets/Atmosphere and overheated Cellulose. Moisture in oil can be Shown as Free Water and Dissolved Water. Interfacial Tension: Determines the cohesive strength of the oil. As oil breaks down, its ability to resist moisture absorption reduces. Think oil and water don’t mix. Restaurant with old oil will have greasy food because the oil is old and full of moisture.

Data Collection, Analysis and Trending Very Important to keep good records. Location, temperature, equipment size and type, serial numbers, and other pertinent info. With DGA, the first year (sample cycle) is the most difficult to diagnose because you do not have any previous data. You will still be able to see some problems, due to spikes in gas levels and ratios being off. As you start to trend data over the years (sample cycles), you will be able to notice when the oil is beginning to degrade due to an issue or when you may need to maintenance the equipment. Sometimes you may get data back that is much different from what you have seen in years past or is much different from other similar pieces of equipment. Usually the best option is to take another sample before making any decisions about the equipment. We have over 300 regulators on our system, so records are very important. Sometimes you just get a bad sample.

What We Have Found With DGA Burnt/Damaged Contacts These were regulators that were in service. They were removed due to gas build-up. We removed these before a small problem could turn into a big problem.

Leaking/Damaged Gaskets Allowing Moisture In

Making a DGA Kit You will need fittings to use on the main drain valve. Do not use the sample valve. Try to use only Tygon tubing, vinyl tubing can be used if Tygon is not available Complete your kit with Teflon pipe compound, waste containers, and a thermometer. Explain why not to use the sample valve. Need to change tubing often or if different types of equipment are being tested. Temperature of the oil is very important (for moisture)

Taking a Sample SUBHEAD HERE SUBHEAD HERE SUBHEAD HERE After draining about 1 pint (on a 1” valve) fill your bottle about halfway, swirl around, dump, and refill. Leave about 1” in neck for expansion. Fill syringe using down pressure from oil. Fill once, then push out into waste, then fill again. Fill to the 50mm level. Mark bottle with the same number as on the syringe. Pack syringe in supplied box and make sure to include all paperwork. Explain why I’m rinsing bottles and syringes. Push out as many bubbles from syringe as you can.

Any Questions? Bryan Harbuck Bryan.Harbuck@peci.com 830-868-4795 04/19/2017