What are the causes of transformer aging?

The aging of the transformer is because the correct use of the transformer is not paid attention to, the loss of the transformer is relatively large, and the failure of the transformer is more. In the production and construction of transformer loss often appear problems we give you to summarize and summarize the following problems:

First, transformer manufacturers to prevent overload operation

Most transformers use A* insulation material with an allowable temperature of 105 ° C. The higher temperature of the transformer is the iron core and coil, the upper oil temperature is followed by the lower oil temperature. The measuring coil temperature is the average temperature, which is about 10 ° C lower than the hot spot temperature, so the upper oil temperature can not exceed 85 ° C. (The temperature is increased to 95 ° C on the basis of 85 ° C, and the oxidation rate is doubled.)

Relation between temperature and temperature rise: Allowable temperature = allowable temperature rise +40℃. Therefore, when the ambient air temperature is greater than 40 ° C, the transformer is not allowed to be at full load. At present, it is generally believed that when the winding insulation temperature of the oil-immersed transformer is higher than 95 ° C-98 ° C, the transformer has a normal service life of about 20 years.

If the temperature is 105℃, the service life is about 7 years, and the temperature is 125℃, the service life is about 2 years. Only the upper oil temperature and its temperature rise do not exceed the allowable value, in order to ensure the transformer manufacturer's transformer safety for the longest period of operation.

Overload operation accelerates the irreversible aging of transformer and shortens the life of transformer. For example, in the insulation oil chromatography analysis of a power supply bureau in 1996, it was found that the total hydrocarbons of 7 110-220 kV transformers exceeded the standard, which was caused by local overheating, and the local overheating of 7 transformers was limited to run immediately after the incident to prevent local overheating of the transformer.

Second, transformer manufacturers to prevent transformer outlet sudden short circuit

The power system capacity is large, the load side outlet short-circuit current is large, resulting in a high probability of transformer damage. In order to fully operate the transformer, the following measures are taken:

1, change the 10 kV neutral grounding method. Urban cable lines are many, the implementation of 10 kV neutral point through 16Ω resistance ground operation. After the neutral point is grounded by the resistance, when the single phase is grounded, the resistance can release the accumulation of half wave charge after the arc quenching, reduce the amount of oscillation, reduce the zero sequence potential, slow down the recovery voltage rise rate, and greatly reduce the overvoltage amplitude and the probability of overvoltage generation.

2. There are more overhead lines in the suburbs, and automatic tuning arc-suppression coils are installed at 10 kV neutral points in substations. The change of the 10 kV neutral grounding mode eliminates the possibility of single-phase grounding transforming into three-phase short circuit and prevents three-phase short circuit burning the transformer at the transformer outlet.

3. The 10 kV equipment in the substation adopts fully enclosed reinforced insulated vacuum switchgear. All new substations shall use fully enclosed vacuum switchgear. The old substation adopts 10 kV transformer outlet and high voltage chamber busbar insulation, and strengthens the oil-free transformation of 10 kV switchgear and full working condition transformation in the national power system to strengthen the insulation of 10 kV equipment.

4, change *10 kV distribution room operating environment. The operating conditions of *10 kV distribution room were improved by closing, dehumidifying, cleaning regularly and installing air conditioning in important distribution room.

5, install the line zinc oxide arrester and distribution explosion-proof zinc oxide arrester, reduce the system overvoltage level. Strengthen the transformation of the distribution network. The operating conditions are modified to reduce the short-circuit accident rate.

Third, transformer manufacturers use fully sealed transformers

The fully sealed transformer isolates the transformer oil from the air and reduces the oxidation of the oil. Strengthen the maintenance of sealed capsules and nitrogen filling measures for non-fully sealed transformers.

Partial discharge refers to the discharge that occurs between the electricity but does not run through the electricity, which is due to the weakness in the insulation of the equipment or the lack of electricity caused by the production process, and the phenomenon of repeated breakdown and extinction under the action of high electric field strength.

It is manifested as the breakdown of the gas in the insulation, the local breakdown of the solid or liquid medium in a small range, or the local breakdown and discharge caused by the concentration of field intensity at the edge and sharp corner of the surface. However, if the insulation of the electrical equipment continues to appear partial discharge at the operating voltage, these weak discharges will have a cumulative effect that will gradually degrade the dielectric properties of the insulation and expand the local deficiency, and then lead to the breakdown of the entire insulation.