Oil immersed type distribution transformers are used to change the input and output voltages up to 36 kV voltage level with capacity of 5000kVA power in desired ratios. The heat generated during operation is maintained and cooled at the normal temperature level with transformer oil. This type of transformer can be examined under two main tank type as hermetically sealed and conservator tank.
Hermetically Sealed Oil Type Distribution Transformers
They are produced in a range of 25 - 5000 kVA, up to 36 kV medium voltage level, with three or single phase, mineral oil or ester fluid, naturally cooled (ONAN or KNAN), with manual(off-load) or automatic(on-load) tap changer, used both external and internal. Hermetically sealed oil type distribution transformers are manufactured by filling the oil under vacuum by balancing the oil pressure and atmospheric pressure at the desired temperature and not to allow the cooling oil to come into contact with the atmosphere.
As a result of changing oil pressure due to thermal changes in hermetic oil type distribution transformers, the internal heat is controlled by natural conservator and contraction of boiler wave walls. Mechanical design and manufacturing are made to withstand these effects.
Hermetically sealed oil type distribution transformer’s footprint shorter than a conservator tank transformer. Therefore, it can be used in smaller areas.
Since the oil does not come into contact with the atmosphere in hermetically sealed transformers, therefore transformers called maintanance free type.
Transformer with Conservator Tank
They are produced within a power range of 25 - 5000 kVA, up to 36kV medium voltage level, three phase or single phase, oil immersed, ONAN, ONAF, OFWF, KNAN, KNAF, KFWF with manual(off-load) or automatic(on-load) tap changer, used both external and internal.
Transformer with conservator tank is the same as hermetically sealed transformers with core and coil structure. The dimensions of the conservator tanks of this type of transformers are designed and manufactured as a result of calculations to store the conservator of the oil whose volume increases with temperature.
Since the transformers with conservator tanks are open to the atmosphere, the oil pressure is changed due to thermal effects, and the air exchange is ensured by taking the moisture of the air through the silicagel (air dryer) in the transformer tank.
As a result of the air exchange due to the temperature differences after usage, the transformer with the working conservator tank loses its silicagel properties over time and causes the humidification of the oil and its structure. For this reason, it is necessary to carry out maintenance such as changing the silica gel and measuring the puncture voltage by sampling the oil.