Periodic Testing of Dry Type Transformers
Periodic Testing of Dry Type Transformers
(OP)
I'm aware that different scopes of transformer testing have been covered here previously, and am also aware that there can be quite a number of factors involved in choosing a testing regime.
I'm interested in the feasibility of testing such as tan delta / dielectric loss angle for smaller dry type LV isolation transformers. The transformers are installed in marine vessels, and range between 35 to 70kVA. The current regime is insulation testing yearly, with no load loss testing and winding resistance testing every two years.
My understanding is that tan delta is only useful if periodic testing and recording of test results is done (in much the same way that dissolved gas analysis is), but its unclear to me as to whether such a measurement is likely to indicate a problem for an LV only isolation transformer, and also what time interval would be needed in order to make it viable.
I'm well aware that its well below the scale of size for anyone to normally bother with for testing such equipment, but does anyone have any considerations on whether it'd be useful to add it to an existing testing regime?
I'm interested in the feasibility of testing such as tan delta / dielectric loss angle for smaller dry type LV isolation transformers. The transformers are installed in marine vessels, and range between 35 to 70kVA. The current regime is insulation testing yearly, with no load loss testing and winding resistance testing every two years.
My understanding is that tan delta is only useful if periodic testing and recording of test results is done (in much the same way that dissolved gas analysis is), but its unclear to me as to whether such a measurement is likely to indicate a problem for an LV only isolation transformer, and also what time interval would be needed in order to make it viable.
I'm well aware that its well below the scale of size for anyone to normally bother with for testing such equipment, but does anyone have any considerations on whether it'd be useful to add it to an existing testing regime?






RE: Periodic Testing of Dry Type Transformers
You can also monitor tan delta. As per Doble 1989 conference paper, typical PF for ventilated /open dry type transformers is 2 % (for HV & HV-LV) and 5 % for LV. For encapsulated units, overall PF is 1 %. Modern day cast coil transformers have a PF 0.8-1 %.
RE: Periodic Testing of Dry Type Transformers
Tan delta is used on larger transformers and equipment rated for more than 600 V (2.4, 4,160, 13.8 kV and more...) where insulation resistance is more exposed to corona and other discharge current problems. Given the importance of those larger equipment, being able to detect a problem before something bad happens is critical. Tan delta test is just more accurate than a megger test. That being said, if you already own a tan delta tester, there is nothing wrong in using it on your transformers.
RE: Periodic Testing of Dry Type Transformers