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What is DGA test in Transformer and how to DGA test ?

If you are going to give an interview as Electrical Supervisor, then many question asked in interview from transformer DGA test. but many people have doubt in DGA test.

In this post we will discuss all the important question related to DGA test. So let’s first talk about what is DGA test in a transformer. Then we will understand other question like: what are DGA test benefits and how to do it?

What is DGA test in Transformer?

Friends, the first question in the interview asked What is full form of the DGA test.

DGA: Dissolved Gas Analysis

If we understand the meaning of its full form, it means that the analysis of which gas has been dissolved in our transformer oil is called DGA.Transformer-Oil testing

If we understand in more simple words what is DGA test, then the DGA is test of transformer oil, in which we find out which gas is dissolved in transformer oil. Friends, you may also asked in the interview that what is the function of oil in a transformer?
So friends, first of all we should know the function of oil in the transformer, then we will understand what we get by doing DGA test of oil.

What is working of oil in Transformer?

Friends, there are many benefits of oil, but if we talk about the main benefits, then it has two main benefits:

  1. To provide insulation to the winding of the transformer.
  2. Cooling the transformer.


Apart from this, another benefit is that we can estimate the transformer’s life and check whether the transformer needs maintenance or not.

For Example: by doing our blood test, we get to know about our health, whether our body is working properly or not, what problem can come in the body. Similarly, when we do DGA test of oil inside our transformer, then we know the health of our transformer from that. Like whether the transformer needs maintenance or not, if any fault has occurred. transformer maintenance

After this you may also be asked when you should do the DGA test. So let us know when and how DGA test is done in transformer.

When and how to do DGA test?

Friends, if we talk about normal, then DGA test is done once in every 6 months. But in some cases we do DGA test transformer once in a year. Now let’s talk about how to do DGA test and how to find out the health of transformer.


Inside the DGA test, the gas that is formed in our transformer oil, we find out which gas it is. Now the question will come that from where did this gas come inside the transformer.

At that time you have to answer that when the transformer is in running condition, along with electrical stress, some mechanical stress also occurs. So now understand what this electrical stress and mechanical stress means.

What is Electrical stress and Mechanical stress in transformer?

When the transformer is in running condition, the voltage connected is changing with time. As the voltage is increasing and decreasing, the current is also less and more. Due to this there is stress on the winding and connection of our transformer.
Along with this, when our transformer is in running condition, there are vibrations in it. So mechanical stress is also generated on our transformer.transformer-stress

So due to these stresses heating and sparking starts in our transformer. Due to sparking in transformer, oil starts heating and its heat increases and this oil becomes overheated. Now when our transformer gets too hot, we call that condition overheating.

So due to this overheating our oil gets decomposed. That means oil starts producing gas.

Note: Transformer oil generates different gas depending on its temperature. For example, at 150’C, our transformer starts to overheat. And when the transformer heats up to 160’C, then hydrogen gas starts to be generated.

Methane gas at 170’C and then oxygen nitrogen and so on, our transformer produces different gases at different temperatures.

But after some time our oil cools back, due to which gas mixed in our oil. So whenever we do DGA test, at that time, we only check which gas is mixed in our transformer. Mean by analyzing the gas of the transformer, we know about the health of our transformer.

For example, if there is hydrogen gas in the oil, it means that our transformer is heated to 160’C and if heated up to 250’C, it will produce a different gas. In this way, we find out the health of the transformer. Friends, you should know one more thing what other benefits we get from doing the DGA test?

What are the advantages of DGA test in transformer?

  1. Friends, the first advantage of the DGA test is that with the help of this test, we can estimate which fault can come in our transformer.
  2. Friends, if we have repaired our transformer, then by DGA test, we can find out that even after repair, there is no fault left in our transformer.
  3. Apart from this, friends, DGA test helps us to know when we have to do the maintenance of the transformer or if our transformer is damaged, it will have to be replaced.

We hope that you get all the information related to the DGA test of transformer. If any question left then you can comment out below or you can send question to us on Instagram Electrical Dost.”

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