1. Classification of test transformers

1. According to the number of phases of a single transformer, test transformers can be divided into three-phase test transformers and single-phase test transformers.

In three-phase power systems, three-phase test transformers are generally used. When the capacity is too large and limited by transportation conditions, three single-phase test transformers can also be used in three-phase power systems to form a transformer group.

2. According to the number of windings, it can be divided into two-winding test transformer and three-winding test transformer.

Common transformers are dual-winding transformers, that is, there are two windings on the iron core, one is the primary winding and the other is the secondary winding. The three-winding test transformer is a transformer with a larger capacity (above 5600 kVA), which is used to connect three different voltage transmission lines. In special cases, there are also test transformers with more windings.

3. Classified according to the structure, it can be divided into iron core type test transformer and iron shell type test transformer.

If the winding is wrapped around the iron core, it is an iron core type test transformer; if the iron core is wrapped around the winding, it is an iron shell type test transformer. The core type test transformer and the iron shell type test transformer are slightly different in structure, and there is no essential difference in principle. Power transformers are generally of iron core type.

4. According to the insulation and cooling conditions, it can be divided into oil-immersed transformers and dry-type transformers.

In order to strengthen the insulation and cooling conditions, the iron core and windings of the transformer are immersed in a tank filled with transformer oil. In special cases, such as street lamps and mine lighting, dry-type transformers are also used.

5. In addition, there are some special purpose transformers. For example, high-voltage transformers for testing, transformers for electric furnaces, transformers for electric welding and transformers used in thyristor circuits, voltage transformers and current transformers for measuring instruments.

2. Classification of oil-immersed test transformers

When the oil-immersed test transformer is in operation, the heat of the winding and the iron core is first transferred to the oil, and then to the cooling medium through the oil. The cooling methods of oil-immersed power transformers can be divided into the following types according to their capacity:

1. Natural oil circulation and natural cooling (oil-immersed self-cooling)

2. Forced oil circulating water cooling

3. Natural oil circulation air cooling (oil-immersed air cooling)

4. Forced oil circulating air cooling

3. Oil-immersed transformers should pay special attention to their fire safety measures:

1. The fire separation distance between oil-immersed transformers with an oil volume of more than 2500kg and oil-filled electrical equipment with an oil volume of 600kg-2500kg shall not be less than 5m.

2. When the distance between the outer wall of the factory building and the outer edge of the outdoor oil-immersed test transformer is less than that specified in the specification table, the outer wall shall adopt a firewall. The distance between the wall and the outer edge of the transformer shall not be less than 0.8m.

3. Only fire partition walls or fire water curtains can be set between single-phase oil-immersed test transformers. When the fire separation distance between two adjacent oil-immersed transformers does not meet the requirements, a fire partition wall or the top of the fire partition wall should be installed with fire-resistant water. .

4. When the single oil volume of oil-immersed transformers and other oil-filled electrical equipment is more than 1000Kg, oil storage pits and public oil collection basins should be set up.

5. When the outer wall of the factory building is within 5m from the outer edge of the oil-immersed test transformer, no doors, windows and holes shall be opened under the total thickness of the transformer plus the horizontal line of 3m and within the range of the outer edges of both sides plus 3m; The fire resistance rating of oil-immersed test transformers for doors and fixed windows on the firewall shall not be less than 0.9h.

6. Oil-immersed test transformers should be equipped with fixed water spray and other fire extinguishing systems in accordance with current relevant regulations. The oil-immersed test transformer should be installed in a separate room, and the door of the room should be a Class B fire door that opens outwards, and directly leads to the outside of the house or the corridor, and should not open to other rooms.