1. The dangers of hydrogen leaks. ① The rated value of hydrogen pressure cannot be guaranteed, thereby affecting the power of the generator. ② Excessive hydrogen consumption leads to frequent hydrogen production and high costs. ③The generator system may catch fire or explode, causing damage.
2. The path and location of the hydrogen leak. Two ways: 1. External leak. There is a leak in the generator body, causing hydrogen to leak into the atmosphere. 2. Internal leak. ① The adjustment sensitivity of the balancing valve of the sealing oil system is not good, and the oil leaks from the hydrogen side to the air side, enters the air side fuel tank, and is discharged into the atmosphere with the exhaust fan. ② There is a leak in the stator coil cooling water pipe. The hydrogen pressure in the machine being slightly higher than the pressure conconstant cold water, hydrogen gas enters the constant cold water system. ③The copper pipe of the hydrogen cooler is leaking, causing hydrogen to enter the open cold water system. ④Leak in closed busbar.
Common locations of hydrogen leakage: ① Hydrogen leakage at the joint surface between the end cover and the machine base. ② Hydrogen leaks from the joining surfaces of the end cover and the end cover as well as the upper and lower half covers. ③The joint surface between the end cover and the seat of the sealing tile. ④ Hydrogen leaks from the stator lead wire housing. ⑤ Corrosion of the rubber pads at the joint surface between the upper and lower flanges of the hydrogen cooler and the housing or breakage of the cooling pipe causes hydrogen leakage and failure of the coolerhydrogen ur:
1. The cooler causes cracks due to wear or thermal stress deviation. Mainly due to the material of the cooling water pipe and the quality of the cooling water. The temperatures of cold hydrogen at the chiller outlet and hot hydrogen at the inlet are typically 39°C and 45°C, and the temperatures at the inlet and outlet of the cooling water open are 2 to 7°C (winter). Heavy condensation occurs because the cooling water temperature is too low.
2. The manufacturing process of the cooler is poor. The cooling water pipe and the tube sheets at both ends are embedded using the pipe expansion method, and cracks are likely to occur at the interface. This fault has currently appeared in the hydrogen cooler, exciter air cooler and air cooler.air with electric pump. ⑥ The hydrogen pipeline cutoff door is not tight, causing hydrogen leakage. ⑦Leak in the cold water system in the stator winding. ⑧Hydrogen is leaking inside the sealing tile, and the gap between the sealing tiles is improperly fitted.
3. How to find a hydrogen leak. ① To detect leaks after the unit is shut down, generally perform an airtightness test of the generator after replacing the air with hydrogen. ② To detect leaks in the generator during operation, use a hydrogen trace analyzer to find the location of the hydrogen leak. If hydrogen is detected on the cooling water discharge side of the hydrogen cooler, it should be determined that the cooler is leaking; if the nitrogen flow meter at the top of the stator cooling water moves, it should be determined that the cooling water pipe isstator failure is detected; leaked. ③ Install an online continuous hydrogen leak monitor. After finding the hydrogen leak point, if it is at the generator end cover or some joint surfaces, it can be sealed with sealant; If there is a leak in the hydrogen cooler, it can be isolated individually. For 300 MW generators, it can be isolated there. There are usually four groups of eight. For the cooler, a single insulation has little effect on the power of the generator, but it causes a large temperature difference at the hydrogen outlet of the hydrogen cooler, which is harmful to a certain extent. Additionally, if operation resumes under high load conditions, the hydrogen temperature at the outlet of other normally operating coolers will also change, making it very difficult for operators to adjust. Currently, according to the priMain hydrogen leakage from generators in various power plants, hydrogen cooler is used. Some leaking cooling water pipes are sealed with caps, which reduces the number of effective cooling pipes and affects the cooling effect and repeated insulation. the connection causes significant work. Depending on the number of years the generator has been in operation, it should be completely replaced when the unit is shut down for maintenance.New cooler. If it is determined that there is a leak in the stator cooling water pipe, the machine can only be stopped for treatment.
4. Damage caused by excessive hydrogen humidity to generators. ① Reduce the insulation level of the stator end winding, causing discharge channels along the insulation surface. ② Reduce the insulation resistance of the rotor and accelerate the occurrence of faultsgrounding or short circuits between turns in the rotor windings which already have insulation defects. ③Accelerate the initiation and expansion rate of hydrogen-induced cracks in the rotor protection ring.
5. The main sources of water and the reasons for excessive hydrogen humidity. Main water sources: ① There are leaks in the cooling water circuit and the hydrogen cooler pipeline in the stator winding. ②Replenish the moisture provided by hydrogen. ③The sealing tile leaks oil and brings moisture into the machine. Defects in the steam seal structure of the turbine ---- main oil system ---- main oil tank ---- generator seal oil system ---- hydrogen system ---- inside the generator. Main reasons: ① The water content of the sealing oil is too high. ②The sensitivity of the valveThe balance of the sealing oil system is too low.
6. Main technical measures. ① Using a high-sensitivity balancing valve and changing the structural arrangement from horizontal to vertical achieves better results. ② Install a vacuum dehumidification device at the inlet of the sealing oil system. ③Improve the dehumidification effect of hydrogen dryer. Measures to improve the effect of hydrogen dryer: 1. Increase the hydrogen flow rate and reduce the humidity at the dryer outlet. 2. The dryer runs continuously. 3. When the unit is stopped and the generator maintains hydrogen pressure, the dryer should continue to operate. The goal is this: all internal components of the machine are at low temperature, the seal oil system still works, water still accumulates, and the circulation of hydrogen in the machine stops. All this is possibleTHE. The hydrogen humidity in the local space near the sealing tile can increase quickly and easily reach the dew point.
For drying hydrogen in 300 MW generators, a condensation hydrogen dryer is mainly used. Its principle is as follows: a refrigeration device using a Freon compressor creates a sealed condensation space at low temperature when part of the hydrogen moist. passes through this gap, the moisture of the wet hydrogen condenses into dew and remains in the device, and is discharged regularly to achieve the purpose of drying the hydrogen. Factors affecting the hydrogen dryer: the temperature of the condensing space of the refrigeration appliance. The lower the temperature, the better the effect. This factor is related to the power, space volume, wet hydrogen flow rate and temperature of the refrigeration device. The use of this typeThe dryer has some disadvantages:
1. The outlet temperature of the dryer can only reach -10℃~-20℃, and its drying degree is limited. Frost will continue to form on the heat exchange surface, resulting in increased thermal resistance and decreased drying performance. The defrost heater will cause the dryer to run intermittently and the hydrogen humidity in the machine will increase. Currently, a generator is usually equipped with two hydrogen dryers. Check if the operating mode is correct to ensure that both dryers work alternately.
2. The external circulation system has not changed and is still driven by the pressure difference from the fan at the generator end. After shutting down the unit, the problem of loss of drying treatment in the machine persists. Therefore, once the generator is out of service, it must be restoredreplaced by air as soon as possible to avoid condensation of hydrogen inside the machine.
3. The return temperature of hydrogen is low (5℃-20℃) and the temperature of cold hydrogen in the machine reaches 40℃, before the two are mixed , it is quite possible that the stator end winding or part of the rotor protection ring is continuously exposed to low temperature hydrogen feedback for a long time, posing a threat to its safe operation.
Considering this phenomenon in generators, it should be considered whether a new regenerative adsorption drying system can be selected when selecting hydrogen drying equipment.
1. First, block the exposed end of the outlet pipe to the outside of the air-cooled hydrogen cooler.
2. Second, fill the inlet water chamber of the air cooler andof hydrogen with water through the water inlet pipe.
3. Finally, it flows through the multiple water pipes of the air hydrogen cooler, and then flows to the outlet water chamber to complete the water filling of the air hydrogen cooler.