Construction

Designed to be completely sealed from the atmosphere. The internal pressure is set during oil filling using special equipment. When the transformer operates under load, heat causes the insulating oil to expand. This expansion is accommodated by the elastic corrugated tank walls, which expand and contract and also provide cooling. Oil filling takes place in special vacuum chambers to ensure that the transformer is completely filled with oil, with no air inside. The core and winding structure is the same as that of a conservator-type transformer.

Advantages

• Because the transformer is sealed from the atmosphere, the insulating oil does not come into contact with oxygen, eliminating insulation deterioration caused by oxidation. This extends the insulation life and therefore the service life of the transformer.
• Under normal operating conditions, no periodic maintenance is required apart from cleaning.
• Without a conservator tank, the overall height is lower, providing an advantage in substations with height restrictions.

Main Disadvantage

• Options for on-site intervention, maintenance and repair are limited. Whenever the hermetic pressure setting is or may be disturbed, the pressure must be reset under vacuum using the necessary equipment.

•  Conservator-Type Distribution Transformers

Technical Specifications

• Power Range:  All standard and intermediate ratings from 25 kVA to 2500 kVA
• Voltage Range: All voltage levels from 0 to 36 kV
• Number of Phases : Single-phase or three-phase options
• Tap Changer Type: Off-circuit or on-load tap changer
• Cooling Method: ONAN and/or ONAF
• Installation Location : Indoor and/or outdoor
• Loss Class : Standard class A (AoAk); optional specifications to suit customer requirements
• Conductor Type : Aluminium and/or copper
• Terminal Type: Porcelain bushings, plug-in, cable box or side outlets

Construction

Designed to communicate with the atmosphere. No pressure setting is required; only the insulating oil level needs to be set. The conservator accommodates oil expansion by allowing air to leave and re-enter its internal air space. It is sized for the maximum oil expansion, and the filling level is set accordingly. Air passes through a breather that removes moisture and is replaced when saturated.

Advantages

• No dangerous pressure will build up inside the transformer, so pressure problems will not occur under overload conditions.
• Metal deformation is reduced because the tank does not need to expand.
• Its construction is more suitable for on-site maintenance and repair.

Main Disadvantage

• It contains components that require periodic inspection, testing, replacement and maintenance.