Light gas alarm for rectifier transformer
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The rectifier transformer is cooled using an oil-air cooler. Shortly after the oil pump is started, a bubble will gradually appear at the glass sightglass on the pump shaft, and this bubble will get larger over time. In the sightglass of the gas alarm, a large amount of substance resembling dust can be seen in the oil (I think these might be very small bubbles). Over time, the low-level gas alarm will go off, and gas will also appear in the large sightglass located below the oil reservoir. It turned out that a similar situation had occurred with one rectifier transformer as well. At first, it was suspected that air was getting in; two sets of fans that were suspected to have leaks were replaced (there are three sets of fans per rectifier transformer). After that, operating any two sets of fans posed no problem, but when all three sets were used, a large amount of dust-like particles could be seen in the oil inside the gas alarm’s sight glass. Eventually, the problem was resolved by reducing the outlet valve of one of the oil pumps by half. But this method doesn’t work on this transformer now.
What load can your transformer handle? Generally, it is advisable for the active load on a transformer to be between 75-80%; exceeding 80% will cause severe overheating in the transformer, degrade its operating conditions, and accelerate the release of gases from the transformer oil. Of course, quality issues with the transformer itself, as well as faults in the transformer, can also cause an increase in the amount of gas released by the transformer oil. Based on your description of the transformer’s behavior, the possibility of a fault condition is low.
The primary side of the transformer is at 35 KV, the maximum voltage on the secondary side is 279 V, and its capacity is 15,000 KVA. It has 19 voltage regulation stages. One transformer is equipped with two rectifier cabinets; each rectifier cabinet can deliver a maximum DC voltage of 318 V and a current of 19 KA, although the maximum current during normal operation is only 16.5 KA. What is the temperature you’re referring to as excessive overheating? Our transformer has been in use for about 8 years, and it has been functioning well all this time. By the way, how often should transformer oil be replaced? Will this phenomenon occur if the dielectric strength of the transformer oil is insufficient?
The maximum allowable temperature for controlling the rise in transformer oil temperature is 45 degrees. The conventional temperature limit is generally set at 75 degrees Celsius (for reference only). According to the current value you mentioned, there should be no problem. The quality of transformer oil can be regularly tested and analyzed by the local power supply department. If the hydrocarbon gas content in the oil sample is too high, it indicates that there is discharge inside the transformer, or that the transformer oil needs to be filtered or replaced.
Our company is capable of conducting voltage tolerance tests on its own. The voltage tolerance value obtained just now was 36; this value was achieved after performing 5 tests, and it represents the average value, with the lowest value being 33. Currently, the transformer is operating with two sets of fans (one of them is leaking oil; it was the cause of the initial mild gas alarm) ； The other one has bubbles at the pump shaft; there are still bubbles there. No dust-like substance appears in the viewfinder of the gas detector. The current maximum temperature of the transformer is 62 degrees; based on the temperature at that time, the temperature rise definitely does not exceed 30 degrees. I also plan to go to the power supply company next to conduct a comprehensive analysis. Finally, I hope someone who is an expert in moving equipment can analyze the reasons
It is recommended to have a spectrum analysis test conducted at the electricity utility to determine whether the transformer is functioning properly.