About Sampling of Transformer Oil
For in-service Oil filled electric Transformers, sampling of the Oil provides a method to determine the condition of the solid and oil insulation as well as the operating condition of the Transformer without opening or de-energizing the Transformer.
Sampling provides a means to check the condition of oil in storage, whether it be new or used, and to determine if it complies with company specifications.
An Oil Sample has to be a representative and maintain the properties & contents of the bulk Oil insulation present in the Transformer. Periodical Testing of the Oil in the Transformer is needed to ensure its Repeated Performance & Long Life of the apparatus.
Sampling the Oil to be Tested is the FIRST concern which will ensure accurate results of the Oil
While sampling the representative Oil one must check for foreign matters including Water droplets, Sediments, Suspected Clear Fibers, Headspace Air, etc.
Critical initial On-Site visual inspection of the presence of any foreign matter in the oils should be detected at the time of sampling itself.
Identifying a Poor Sample and the decision to resample should be made & executed prior to leaving the On-Site.
Outages due to faulty Transformer Oil Analysis could have an adverse snowballing effect on the electrical connections.
Tests include :
(1) Dissolved Gas Analysis (2) Water (3) Dielectric dissipation factor (4) Particles (5) Breakdown voltage (6) Other chemical & physical tests