A Quick Guide to Transformer Oil Testing: Understanding Your Results

At SDMyers, our customers know that oil testing is essential. It keeps a transformer functional and extends its life. Testing does produce a lot of data, however, and it can be a challenge to understand what all that information means.

Here is a handy reference to help you grasp the fundamentals of oil testing and how your results can impact the reliability of your transformer.

 

DISSOLVED GAS ANALYSIS

UNDERSTANDING DISSOLVED GASES

New transformer oil contains small amounts of dissolved combustible gases. Additional dissolved combustible gases form when an abnormal condition exists, which is often attributed to a fault. By measuring the concentration of a gas in transformer oil, it is possible to narrow down what event caused it to form, how severe or recurrent that event was, and whether the transformer is still reliable. Here are a few examples:

HYDROGEN

Hydrogen accompanies most known transformer faults. An excellent indicator that further analysis is needed.

ACETYLENE

Presence of acetylene is an indicator of arcing/sparking and severe overheating. Fault temperatures can be determined by comparing concentrations of dissolved acetylene, ethylene, and methane.

METHANE

The presence of methane indicates low energy electrical or thermal faults. Fault temperatures can be determined by comparing concentrations of dissolved acetylene, ethylene, ethane, and methane.  

ETHANE

The presence of ethane indicates electrical or thermal faults, with production of ethane starting at around 250 degrees Celsius. Fault temperatures can be determined by comparing concentrations of dissolved acetylene, ethylene, ethane, and methane. 

ETHYLENE

Like acetylene, ethane, and methane, Ethylene indicates a thermal fault. Fault temperatures can be determined by comparing concentrations of dissolved acetylene, ethylene, ethane, and methane. The higher the temperature of the fault, the greater the concentration of Ethylene.

OXYGEN

The presence of oxygen suggests ingress of outside air into the transformer tank and greatly increases the conditions that lead to accelerated degradation of the cellulose insulation.

CARBON MONOXIDE

Elevated levels of carbon monoxide and carbon dioxide are indicators of possible cellulose insulation degradation.

CARBON DIOXIDE

Elevated levels of carbon monoxide and carbon dioxide are indicators of possible cellulose insulation degradation.

NITROGEN

Nitrogen, as well as oxygen, can be an indicator of air ingress to the tank.

Dissolved gas analysis (DGA) is the industry standard for detecting faults in a transformer. Often, detection of these gases alone does not point to any specific fault. Rather, you need the specific combination, concentration, change over time, and movement from the baseline test results for a true understanding of what is happening inside a transformer.

In interpreting DGA results with our own proprietary method, SDMyers uses internal guidelines. In addition to the gas levels, our DGA interpretations are based on a large number of variables, such as equipment type, liquid type, past history/trending, manufacturer, equipment age, kVA, voltage, gallons, breather type, temperature, and service history, among others.

We also utilize statistical analysis and other industry standard diagnostic tools such as Rogers Ratios, Duval Triangles, and Duval Pentagons, when appropriate. The results either indicate healthy electrical power equipment that maximizes reliable life or diagnoses of fault conditions that closely match what is found in maintenance activities and post-failure forensic investigations.

Find out more about testing and analysis by downloading the SDMyers guide, Understanding Transformer Testing: A Guide to Diagnostic Tests for Oil-Filled Transformers (free download, no signup required). Fill in the form below to request your download.

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MOISTURE CONTENT

UNDERSTANDING MOISTURE

Moisture contributes to conditions that rapidly degrade the solid cellulose insulation inside a transformer. When a Karl Fischer moisture analysis shows unacceptable levels of moisture, that should be removed to prolong the life of the transformer.

A word of warning: many maintenance companies focus on oil cleaning to bring the concentration down and protect the insulation. But cleaning the oil may not dry the paper; there is usually much more moisture in the paper than in the oil. Processing the oil to remove the moisture is a temporary fix. Within days moisture will leach out of the paper and into the oil, and the Karl Fisher reading will be high again.

Find out more about the Karl Fischer test by downloading the free guide, Understanding Transformer Testing:

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CRITICAL TRANSFORMERS

UNDERSTANDING TESTS FOR CRITICAL TRANSFORMERS

For transformers that require close monitoring due to their current condition, their cost, their scarcity or uniqueness, or the critical nature of the equipment they power, SDMyers offers a comprehensive range of tests that pinpoint faults and diagnose potential problems. These tests will help you maximize the life of your transformer.

POWER FACTOR

Liquid Power Factor is a measure of the dielectric losses in an insulating liquid when used in an alternating current electric field. 

INHIBITOR CONTENT

A decrease in the percent weight of the inhibitor is strong evidence that something is happening inside the transformer.

DISSOLVED METALS

Inductively Coupled Plasma (ICP) spectroscopy is the technology used to detect metal dissolved in transformer oil. ICP data is used to corroborate DGA data and identify the location of fault conditions inside the transformer.

FURANS

Furan testing tells us about the condition of the solid insulation inside the transformer in a much less invasive way than taking a physical sample.


Download the free Understanding Transformer Testing guide

For a deeper dive into the testing methods we use to maximize the life of our customers’ transformers, fill in your email address below and receive a free copy of Understanding Transformer Testing: A Guide to Diagnostic Tests for Oil-Filled Transformers. Learn more about test methods, analytical approaches, and the tools SDMyers uses to diagnose faults before they become insipient issues.

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