When purchasing an oil filter, the most common dilemma is whether it is single-stage or two-stage. Double level is much more expensive, but does the value match? Quantifying the core gap between the two makes it easy to judge.
The essential difference in vacuum degree
This is the core difference between single level and double level.
Single stage vacuum pump (rotary vane pump): The ultimate vacuum degree is usually between 10-100Pa, and the working vacuum degree (when oil enters) is about 200-500Pa.
Dual stage system (Roots pump+rotary vane pump in series): HZLY-200A has a maximum vacuum degree of ≤ 5Pa, and the working vacuum degree is much lower than that of single-stage.
The effect of vacuum degree difference of 10-100 times on dehydration and degassing efficiency: under a vacuum of 200Pa, the boiling point of water is about 17 ℃; Under a vacuum of 5Pa, the boiling point of water is as low as about 0 ℃. Similarly, heating the oil to 60 ℃ can evaporate much more water in a two-stage vacuum system than in a single-stage system.
Differences in gas content indicators
Here is a very intuitive set of comparative data:
After treatment with a single-stage vacuum oil filter, the gas content can usually be reduced to 0.5% to 2% (volume ratio), and the water content can be reduced to 10-30ppm.
After dual stage treatment with HZLY-200A, the gas content decreased to ≤ 0.1% (volume ratio) and the water content decreased to ≤ 5ppm.
The difference in processing results between the two is 5-20 times, which is not due to brand differences, but rather determined by physical principles.
What occasions must choose dual level
Oil injection for transformers of 110kV and above: High voltage transformers have strict requirements for the quality of insulation oil, especially the gas content. Bubbles are the root cause of partial discharge in high-voltage fields. The gas content requirement for insulation oil of 110kV transformers is ≤ 3%, 220kV is ≤ 1%, and 500kV is ≤ 0.1% - this last level can only be stably achieved by dual levels.
Ultra high voltage transformer (750kV/1000kV): This type of equipment has requirements for oil cleanliness (NAS level 0) and gas content that can only be met by a two-stage system, and a single-stage system is not even on the same level.
Vacuum pumping operation of transformer body: The vacuum pumping of large transformers (body volume of 20-60m ³) requires a sufficiently large pumping rate. The pumping rate of 1080m ³/h of HZLY-200A can complete the vacuum pumping in a reasonable time, and the single-stage pumping rate is usually only 1/5 to 1/10, with extremely high time cost.
What occasions are single-stage sufficient: 10kV distribution transformers, lubricating oil filtration and purification for small and medium-sized equipment, and occasions that do not require vacuum oil injection, single-stage is more cost-effective.