Dry Power Transformer Aging Prevention Measures

There will be various problems in the operation of dry power transformer. The appearance of such problems is to endanger the normal and full performance of dry-type transformers, destroy the characteristics of dry-type DC transformers, and accelerate the aging of dry-type transformers.

1. Avoid overload operation

Most of the dry-type transformers use A-class insulation materials, and the higher allowable temperature is 105 °C. The higher temperature of the dry-type transformer is the transformer core and electromagnetic coil, the water temperature of the top layer is second, and the water temperature of the next layer is lower. The precise measurement of the electromagnetic coil temperature is the average temperature, which is about 10°C lower than the network hotspot temperature, so the top water temperature should not exceed 85°C. When the temperature is basically raised from 85°C to 95°C, the air oxidation rate is doubled. The relationship between temperature and temperature rise: allowable temperature = allowable temperature rise + 40°C (higher temperature of surrounding gas). Therefore, when the ambient gas temperature exceeds 40°C, the dry-type transformer is not allowed to be overloaded. At this stage, it is generally believed that when the temperature of the oil-to-oil dry-type transformer winding insulation layer is higher than 95°C-98°C, the dry-type transformer has everything normal. The useful life is about twenty years. When the temperature reaches 105°C, the service life is about seven years, and when the temperature is 125°C, the service life is about 2 years. Only when the top water temperature and the temperature increase does not exceed the control value, can the safe long-term operation of the dry-type transformer be ensured.

Overload operation accelerates the irreversible aging of dry-type transformers and reduces the service life of dry power transformer. For example, a power supply bureau found in the transformer oil chromatography in the 1990s that the total hydrocarbons of seven 110-225kV dry-type transformers exceeded the standard, which was caused by some over-temperatures. Dry-type transformers appear part of the overtemperature again.

2. Avoid sudden short-circuit faults at the inlet and outlet of dry-type transformers

The volume of the power supply system is large, and the short-circuit capacity of the inlet and outlet on the load side is large, resulting in a high probability of damage to the dry-type transformer. For the safe operation of dry-type transformers, the following countermeasures are adopted:

1. Change the grounding method of the 10kV neutral point. There are many cable lines in the urban area, and the 10kV neutral line is operated by a 16Ω resistor grounding device. After the neutral line is grounded by the resistor, when the single-phase is grounded, the resistor can release the accumulation of half-wave positive charge after the arc is extinguished, reduce the kinetic energy that causes oscillation, reduce the zero-sequence potential difference, and slow down the rate of increase of the repair working voltage. Greatly reduces 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 coils. The change of the 10kV neutral point grounding method eliminates the probability of single-phase grounding being converted into a three-phase short-circuit fault, and prevents the dry-type transformer from being burned by the three-phase short-circuit fault at the inlet and outlet of the dry-type transformer.

3. The 10kV machinery and equipment of the power distribution station adopts a fully enclosed high-voltage switch cabinet of the vacuum pump with the lifting insulation layer. Fully enclosed vacuum pump high-voltage switchgear shall be used in all substations under construction. The old substation uses dry-type transformer 10kV group outlet and high voltage room busbar cladding insulation layer, upgrades 10kV high-voltage switchgear oil-free renovation and full working condition renovation in the national power supply system, and improves the insulation of 10kV machinery and equipment Floor.

4. Improve the software environment of 10kV high and low voltage distribution room. The operation standard of 10kV high and low voltage power distribution room is improved by adopting closed type, dehumidification, cleaning on time, and the key high and low voltage power distribution rooms are refitted with central air conditioners.

5. Install the active zinc oxide high-voltage arrester and power distribution equipment explosion-proof active zinc oxide high-voltage arrester to reduce the overvoltage level of the system software. Upgrade the power distribution network. Improved operating standards and reduced short-circuit failure failure rates.