Power transformer tanks - a weak link

Often the damage we see in power transformers involves the tank itself. So in this post I'll describe the power transformer tank, and give some tips on maintaining it.

The transformer tank provides the containment for the core and windings and the dielectric oil. The tank acts as the vacuum vessel for impregnating the transformer with oil.

The tank has a removable cover so that core and windings can be accessed and removed. The cover is fastened by a flange around the tank and is bolted. It should be inclined at about one degree to help drain rainwater.

The cover holes are made oil tight using gaskets. These are normally rubber bonded cork or neoprene bonded cork or stiff rubber. The rubber is synthetic rubber, so to resist degradation by the mineral oil. These gaskets joints represent a potential leak, and often is the source of more serious problems that occur due to poor maintanance.

The main tank cover flange usually represents the greatest oil leakage threat, since being of large cross section, it tends to provides a path for leakage flux, with the resultant eddy-current heating leading to overheating and degradation of gaskets.

From our experience, oil leaks are the first visible signs of deeper trouble. Therefore, we highly recommend to visually inspect power transformers on a regular basis. These checks must be done by qualified personnel, as the voltages from power transformers are deadly. checks for leaks around the cover flange, insulator gaskets and other auxiliary equipment are done as part of a routine maintenance check. It is fairly important, as an early diagnosis can save A LOT of money resulting from damage to the transformer later on (due to overheating) and the equipment connected to it (due to shorting) or around it (due to exploding).

Megawatt Transformers provides transformer maintenance that includes thorough testing of the transformer tank's gaskets, transformer oil analysis and transformer repairs. Contact us for more details.

Top maintenance tips for power transformers

Power transformers are expensive machines, and they require regular maintenance like we all do. Here are the top tips to keep power transformers healthy and prolong their service life, roughly in order of importance:

1. Monitor the transformer oil and analyze it regularly: taking oil samples is an essential prerequisite to any maintenance. An oil sample is such an important source of information as to the transformer condition that it is essential that extreme care is taken in obtaining it in order to ensure that the information gained is not misleading. There are strict procedures on how to take a proper sample (e.g. British Standard 5263, or IEC publication 475), but as an owner - make sure that the oil is sampled and analyzed regularly by a professional. Megawatt Transformers has an oil analysis lab and offers oil sample collection and analysis with same day results.
2. Visual inspection: visual inspection of power transformers on a routine basis can provide clues to the condition of the transformer. 'Wet', slow leaking transformers with patches of oil on their exterior indicate a leakage in the seals, a crack in the insulators or damaged fins. Other visual inspection includes the condition of the silica gel aerator for change of color. All these may indicate an impeding problem with the transformer insulation system.
3. Keep clean: keeping the transformer exterior clean and its surroundings tidy facilitates quick spotting of oil leaks. In addition, it helps cooling the fins/cooling pipes. Keeping the surroundings tidy reduces the chances of fire damage should the power transformer overheats. Megawatt Transformers provides complete power transformer maintenance and repair.
4. Check operation of fault analysis devices: The gas and oil actuated relay (Buchholtz) is used extensively to disconnect a transformer from teh supply in case of an interturn (core related) fault or any other internal failure. These are extremely important safeguards, and their operation must be checked periodically. Dissolved gas analysis devices also fall into this same category.