Transformer Oil Testing

Can you tap a pipe thread into it and use a cartridge heater?

Have you tried contacting Hipotronics? They manufacture HV test equipment including oil dielectric testers (you may even be using one of their units?), which are basically an AC hipot for oil. They may be able to give you some suggestions relating to temp variation effects and how to control it.

http://www.hipotronics.com/products/liquid-dielectric-test-equipment/oc60e.php

Whose >breakdown tester are you using? Baur? Megger? Hippotronics? You have to be careful of the cup and the material it is made of. Some cups are made of plastic and may not take the temperature of interest. Generally speaking, the cups are made to be used at room temperature and will change dimensions if heated, . . . including the "test gap" which may become shorter or longer than specified. The actual breakdown voltage would need to be adjusted under such circumstances. You would best heat the test cup in an oven, . . and the oil in a clean SS utensil, . . . then pour the oil into the test cup. Being oil - and not water, . . . the oil and cup will cool slowly. To avoid cooling, . . you may want to install a heater under the protective cover. With a proper size heater - the cooling can be kept to a minimum.

Hi

don't really know why you want to test the oil over a range of temps.. further explanation could help here.

However if you really want to I suggest you heat the oil to the required temp OUTSIDE the test equipment and then put it into the test cup. It is not a good idea to heat the cup which has been pointed out to you that it is usually plastic not metal, and this is for safety and for the purity of the experiment. The problem with inserting a heating element into the cup and/or having a metal cup is the HV MIGHT short to the cup/element and NOT the other side of the probe...

Normally any tests to tranformer oil is conducted at the temp the oil is at when the sample is removed from the transformer, that is within a few minutes of being removed. Oil type is usually selected on the maximum duty temp which is the ambient temp plus projected temp increase.

Also I suggest you contact Shell, who make transformer oil and find out from them the temp ranges & the different types of oil, AND obtain the data sheet for the oil you are wanting to test. Over heating the oil will have an adverse effect on the oil and screw up your experiment.

however if a sample from a suspect transformer does fail in the test equipment, it will fail at ANY temperature (in the test equipment), mainly due to the oil absorbing water vapour and/or its dielectric properties have broken down because it has overheated or been burnt due to a short inside the transformer.

You mention that after 6 tests the oil temp drops. Each test SHOULD have a NEW & FRESH sample of oil, as each time the oil breaks down you degrade its dielectric properties, making the tests follwoing the first one worthless and totally inaccurate

Remember safety first...hot oil will hurt.. and get back to us to let us know what you find

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