There will be various problems in the operation of dry-type transformer, which will endanger the normal operation of dry-type transformer, destroy the characteristics of dry-type DC transformer and accelerate the aging of dry-type transformer. So what can we do to prevent the aging of dry-type transformer?
1、 Avoid overload operation
Most of the dry-type transformers are made of class a insulating materials, and the higher allowable temperature is 105 ℃. The higher the temperature of dry-type transformer is the transformer core and electromagnetic coil, the higher the water temperature of the top layer, and the lower the water temperature of the next layer. Accurate measurement of electromagnetic coil temperature is the average temperature, which is about 10 ℃ lower than the network hot spot temperature, so the top water temperature should not exceed 85 ℃. (when the temperature is 85 ℃, the air oxidation rate is doubled. ）Correlation between temperature and temperature rise: allowable temperature = allowable temperature rise + 40 ℃ (higher temperature of surrounding gas). Therefore, when the ambient gas temperature exceeds 40 ℃, the overload of dry-type transformer is not allowed. At this stage, it is generally felt that the winding insulation layer of oil transformer dry-type transformer is higher. When the temperature is 95 ℃ - 98 ℃, the dry-type transformer has everything, and the normal service life is about 20 years. When the temperature reaches 105 ℃, the service life is about seven years. When the temperature is 125 ℃, the service life is about two years. Only when the top water temperature and temperature increase value do not exceed the control value, the safe and long-term operation of dry-type transformer can be ensured.
Overload operation accelerates the irreversible aging of dry-type transformer and reduces the service life of dry-type transformer. For example, in the transformer oil chromatogram of a power supply bureau in the 1990s, it was found that the total hydrocarbon of seven 110-225kv dry-type transformers exceeded the standard, which was caused by partial overheating. Immediately after the case, the seven transformers that caused partial overheating were put into load limiting operation to avoid partial overheating of dry-type transformers.
2、 Avoid sudden short circuit fault of dry type transformer entrance and exit
Due to the large volume of power supply system and the large capacity of short circuit at the entrance and exit of load side, the damage probability of dry-type transformer is very high. In order to ensure the safe operation of dry-type transformer, the following countermeasures are adopted:
1. Change 10kV neutral grounding method. There are many cable lines in urban area. 10kV neutral line is grounded by 16 Ω resistor. When the neutral line is grounded by resistor and single-phase grounded, the resistor can release the accumulation of half wave positive charge after arc extinction, reduce the kinetic energy causing vibration, reduce the zero sequence potential difference, slow down the rate of high-speed rise of repair working voltage, and greatly reduce the overvoltage amplitude value and the probability of overvoltage.
2. There are many transmission lines in the suburbs, and the 10kV neutral line of the distribution station is installed with automatic tuning arc suppression coil. The change of 10kV neutral point grounding method eliminates the probability of single-phase grounding transforming into three-phase short circuit fault, and avoids the dry-type transformer from being burnt by three-phase short circuit fault at the inlet and outlet of dry-type transformer.
3. The 10kV machines and equipment in the distribution station are fully enclosed vacuum pump high voltage switch cabinet with lifting insulation layer. All the distribution stations under construction shall be equipped with fully enclosed vacuum pump high voltage switch cabinet. In the old distribution station, 10kV group outgoing line of dry-type transformer and high-voltage chamber bus duct are used to wrap insulation layer. In the national power supply system, 10kv High-voltage Switch cabinet is upgraded for oil-free renovation and full working condition renovation, and the insulation layer of 10kV machinery and equipment is upgraded.
4. Improve the software environment of 10kV High and low voltage distribution room. In order to improve the operation standard of 10kV High and low voltage distribution room, closed type, dehumidification, timely cleaning and central air conditioning are selected.
5. Install active zinc oxide high-voltage arrester for lines and explosion-proof active zinc oxide high-voltage arrester for distribution equipment to reduce overvoltage level of system software. Upgrade distribution network renovation. The operation standard is improved and the short circuit failure rate is reduced.
3、 Selection of sealed dry type transformer
The sealed dry-type transformer can isolate the dry-type transformer oil from the air and reduce the air oxidation of the oil. Maintenance of non sealed dry-type transformer and nitrogen charging Countermeasures of dry-type transformer. Partial discharge refers to the charge and discharge generated in the middle of the electrical level but not around the electrical level. It is due to the defects in the insulation layer of machinery and equipment or the defects caused in the process of processing, resulting in repeated penetration and elimination under the effect of high field strength. It is mainly manifested as vapor penetration in the insulation layer, partial penetration of solid or liquid substances in a small scope, or partial penetration charging and discharging caused by the concentration of magnetic field intensity at the edge and oblique angle of the surface layer. However, if the insulation layer of electrical equipment continues to have partial discharge under the operating voltage, this weak charge and discharge will cause accumulated utility, which will make the dielectric and electrical properties of the insulation layer slowly deteriorate and expand some shortcomings, and eventually cause the whole insulation layer to penetrate.
In addition, in the whole process of dry-type transformer operation, we should do a good job in the maintenance of dry-type transformer. Proper application and practical operation can avoid the damage of dry-type transformer at a very large level.
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