These are electrical machines that can step-up or reduce the power output in electrical power applications. The cost of capitalization for an electric power transformer that is in the 100MVA range could be more than $1M and, once it’s in operation, the cost is raised. It is estimated that the average lifespan of the installed big power transformers (LPTs) in the United States is approximately 45 years old, with 70% of LPTs aged older than 30 years. The lead time for LPTs may vary from 1 year to two years. A lot of transformers are nearing an end point in their technological lifespan, and a majority has come to the final stage of their financial lives. Although the lifespan of a power transformer is different under the design and the way they used it older power transformers face an increased chance of failure.
The major challenge for the power industry today, particularly during the COVID-19 timeframe, is to maximize the use from existing assets without compromising the level of customer service. The funds to replace assets might be subject to change, which could cause delays for new installations or renovation. The asset owners and the operations team and maintenance personnel to be aware of the state of the old and, often, heavily overloaded LPTs.
There are many analogies that are associated with the human body within the mechanical and electrical worlds. For instance, the human body acts like an engine which continuously produces large amounts of heat. Its radiator is the one that disperses heat most efficiently in warmer climates. It is possible that most of the people reading this article have had personal experiences with the basic body diagnostics for the human body and are acquainted with a few of the tests for health. I have used the analogy of a human test to explain or instruct the diagnostics of power transformers and it has proven to be a hit. This article attempts to summarize the analogy of a human for diagnosing for power transformers.
The aim in this piece is to aid those who are not engineers or engineers and other people working in the energy industry who do not know of power transformers are aware of the importance of tests and diagnostics used for power transformers’ condition evaluation. This article is not intended to go into the details of diagnostic tests, but it is a brief introduction.
Transformer DGA v.s. Blood Test
Dissolved Gas Analysis (DGA) is a diagnostic procedure similar to your blood test for medical which is used on power transformers. DGA is extremely efficient and robust method and has been in use for over 50 years to safeguard against electrical and thermal failures. The degeneration of transformer oil produces different gases. The most significant ones being H2 – hydrogen and CH4 methane, C2H4 Ethane, C2H6 – as well as C2H2 acetylene. CO, carbon monoxide and CO2 carbon dioxide. It performed annually DGA to ensure good health of big power transformers. A more frequent testing could be necessary when there is a defect found.
Similar to blood tests the syringe sample is removed from the transformer and taken to a laboratory for analysis. The larger sample of oil stored in the jar is also collected along with the syringe specimen to be further analyzed. The equivalent for the sample from the jar might be to the urine specimen which is utilized to provide other health-related details.
DGA is among the most frequently utilized diagnostic tools for the assessment of transformer condition because experience has shown that it is an efficient tool. The new IEEE C57.104-2019 offers the most current standard for the understanding DGA. Similar to blood tests, DGA has limitations that need to be taken care of in order to get a valid test results. Incorrectly collecting samples, incorrect identification or inaccuracy of the test equipment as well as multiple occurrences occurring simultaneously can alter the results.
Heat Run Test vs. Exercise Stress Test
Test for heat run Also known as temperatures rise tests, are a component of the factory acceptance test (FAT) carried out in a HV laboratory with powerful power sources to check the efficiency of the transformer under full load or to simulate short overload conditions. They also used the test for other electrical equipment like generators, motors cable, switchgear and so on.
It is easy to see the resemblance of the heat run test to the test of stress in the human body. A workout (cardiac) stress test will determine how your heart reacts to stress situations when it’s at its most active. Similar to heat run, where several sensors are connected to the tank of the transformer to observe the transformer during a cardiac test, the heart’s response to stress externally in a controlled environment is assessed.
Transformer Heat Run Test vs. Cardiac Stress Test
Furan Test vs. Urine Protein Test
Furan tests are a diagnostic method to determine the degrading of the insulation on transformers. The cellulosic degradation of insulation creates furan (2-furaldehyde) and other byproducts, which are released into oil. In contrast, urine protein tests measure levels of proteins in the urine. People who are healthy don’t have a substantial amount of protein in their urine. However, proteins may be excreted from the urine when kidneys are not functioning properly or when high levels of certain proteins are found in bloodstream. Similar to a urine-protein test an oil sample is taken from a jar. The sample is then sent to a lab to be analyzed for byproducts. In general an electric transformer that has 0.1 percent furan is considered having a normal thermal aging process and an acceptable insulation condition. If the furan is at 1ppm, more investigation is needed. When the furan measured is at 10ppm the transformer is most likely nearing the end of its life.
Summary of Power Transformer & Human Body Analogy
There are a variety of other fundamental and advanced tests used for test the condition of the power transformer, which is comparable to tests in the human body. They provide the overview on the following table, which includes the breakdown of voltage in oil, SFRA, DFR, partial discharge test, and polymerization (DP).
As a doctor one would expect a specialist in transformers to be tends to suggest starting the examination of the condition by performing basic tests, and then move on to more complex tests if needed. When combining the results of several tests together in the hands of a specialist, the transformer expert can identify the likely flaw, defect or health problem that the transformer is in.
Most times this will require “re-rating” the transformer’s planned capacity of load for both the normal and contingent use. In most cases, the application of these load limits can be contingent on the state of the equipment. Refurbishment and options for improving the efficiency of transformers in order to reduce temperatures, extend life and/or improve load capacity are usually considered O&M alternatives to defer the capital expenditure on new equipment.
They base 600MVA Generation Plant Transformer Acoustic Emission PD simulation on real-time onsite AE monitoring to identify internal flaws
The health check-up and evaluation of the condition of power transformers is crucial to ensure the safety and stability of the power system operation. Like humans checking up on the frequency and attention required will naturally increase as how old the equipment. In the past few years they have conducted significant efforts for the creation of reliable and precise method of assessing condition, like monitoring via the internet. I recommend it to look into these methods for the most crucial assets.
It is anticipated that a portion of the public and utility money allocated to the replacement and repair of power equipment will be delayed or canceled because of the COVID-19 health condition. This is why it is more important than ever to assess the health of the old power transformers. It is suggested to employ the most advanced diagnostic techniques and methods to extend the lifespan of existing precious assets.
