Essential Oil Diagnostics: Transformer Oil Sampling | EA Technology
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Essential Oil Diagnostics: Transformer Oil Sampling

  • 09 February 2021

  • EA Technology


When we look at electrical assets such as transformers and we want to know what is going on inside that big grey tank, we generally turn to oil analysis in a bid to determine the condition of the oil and the asset to ultimately give us direction of what needs to be done, if anything.

There are many steps in this process where quality is key and a lot of the time the focus is put on the chosen lab to carry out the analysis on your oils. Having a high-quality lab is vital but often the initial step is overlooked, which is arguably the most critical…sampling!

Now if we get this first step wrong then everything after it follows. It doesn’t matter how good your lab is, imagine a domino effect. The good news is that this first step is simple, if done correctly. It’s about having the correct knowledge and the right tools for the job.

The standard document for sampling is IEC 60475: Method of Sampling Insulating Oils and this is the place to start. It is recommended that all sampling is in accordance with IEC 60475 which details the best practices and the different sample vessels to use dependent on the tests to be carried out.

Step 1

The first thing to consider is: are you adequately trained to be taking the sample yourself or should you be getting an expert in to sample the units for you? Either way you are going to want to know that whoever is taking the sample knows what they are doing.

Step 2

When you look at the options available for sample vessels (and there are more than you think) we would recommend glass bottles with a polycone cap. The reason for this, is that you can get enough  sample in a 500ml bottle to carry out most, if not all your requirements and it is the only vessel (along with flexible metal) that is suitable for ALL standard tests.

Step 3

Now comes the tricky bit, getting the oil from the unit into the bottle and no, turning on the tap and ‘sticking’ a bottle under is not an appropriate method. This will inevitably give you fluctuations and inaccurate oil quality results as you would be pulling in debris, air, moisture etc. from the surrounding environment.

The easiest and best solution is to get yourself a sampling kit or ensure the engineers taking your samples are using one. Here is the type of sampling kit our engineers / clients utilize:

It’s important to keep any sampling kit clean after use so it is kept in a good condition and can then be re-used for future sampling requirements.

There is a step by step process that should be followed and if done correctly will ensure a good quality and representative sample is taken.

  • Clean the sample tap before any sampling is started, use a wire brush and/or lint free cloth to remove and debris form the external surface.
  • Connect the correct size oil resistance rubber bung to the sample tap by pushing or tapping it on and don’t forget to attach the stainless-steel tube to the pre-drilled hole.
  • Always drain at least 500ml of oil out of the unit and to a waste container before taking your sample, this ensures any debris is flushed out before you take your sample…this is VERY important.
  • The temperature of the flowing oil should be recorded and noted on the sample label, this is required for any accurate moisture determination.
  • Attach the bottle bung with inlet tube and air vent tube to the sample bottle. The stainless-steel tube should extent to the bottom of the bottle and ensure a slow flow rate to cause minimum air displacement and oil disturbance.
  • The bottles should be allowed to overflow and tubing should be withdrawn slowly and the bottle should be tipped to allow some oil to flow out leaving approximately 2cm head space . The cap should be securely screwed onto the sample vessel.

The sample should be cleaned, clearly labelled and securely and safely packed in a carry case or box to ensure safe transport to the lab. We will cover this in our next blog, so stay tuned!

So, there you have it, simple but critical and you should have a good quality representative sample to send to your lab……then it’s over to them!