Oct. 19, 2021
Today, Dingbo Power, a diesel generator manufacturer, introduced to major users the hazards of hydrogen leakage of diesel generator sets and some maintenance measures.
1. The hazards of hydrogen leakage from diesel generators.
① The rated value of hydrogen pressure cannot be guaranteed, which will affect the output of the generator.
② Excessive hydrogen consumption results in frequent hydrogen production and high cost.
③The generator system may catch fire or explode, causing damage.
2. How to find hydrogen leakage of diesel generator set.
①Look for leaks after the unit is out of service. Generally, the air tightness test of the generator is done after the hydrogen replaces the air.
②Look for the leakage of the generator during operation, and use the trace hydrogen tester to find the hydrogen leakage location. If hydrogen is detected on the exhaust side of the cooling water of the hydrogen cooler, it should be determined that there is a leak in the cooler; if the nitrogen flow meter on the top of the fixed cooling water moves, it should be determined that the cooling water pipe of the stator is leaking.
③Install an online continuous monitoring instrument for hydrogen leakage. After finding the hydrogen leakage point, if the generator end cover or some joint surfaces, it can be sealed with sealant; if the hydrogen cooler has a leak, it can be isolated individually. For a 300MW generator, there are generally four groups and a total of eight For the cooler, a single isolation has little effect on the output of the generator, but it causes a large deviation in the hydrogen outlet temperature of the hydrogen cooler, which is a certain hazard.Moreover, when the load is high, if the operation is resumed, it will also cause changes in the hydrogen temperature at the outlet of other coolers in normal operation, which is very troublesome for the operators to adjust. At present, according to the main hydrogen leakage part of the generators of various power plants is the hydrogen cooler, some leaking cooling water pipes are sealed with plugs. This way, the number of useful cooling pipes is reduced, which affects the cooling effect, and repeated isolation and plugging cause work. large. For the number of years the generator has been in operation, a new cooler should be completely replaced when the unit is out of service for maintenance. If it is determined that the stator cooling water pipe is leaking, the machine can only be shut down for processing.
3. Excessive hydrogen humidity in diesel generator sets is harmful to generators.
① Reduce the insulation level of the stator end windings, resulting in a discharge channel along the insulating surface.
②Reduce the insulation resistance of the rotor and accelerate the occurrence of grounding or inter-turn short-circuit faults in the rotor windings that have insulation defects.
③Accelerate the initiation and growth rate of hydrogen-induced cracks in the rotor guard ring.
4. Main water sources and reasons for excessive hydrogen humidity in diesel generator sets. Main water source:
① There is leakage in the cooling water circuit and hydrogen cooler pipeline in the stator winding.
②Water brought in by hydrogen supplement
③The moisture brought into the machine by the oil from the sealing tile. The defects of the steam seal structure of the steam turbine-the main oil system-the main oil tank-the generator sealing oil system-the hydrogen system-inside the generator. main reason:
①The water content in the sealing oil is too high.
②The sensitivity of the balance valve in the sealing oil system is too low.
5. Main technical measures for hydrogen leakage of diesel generator sets.
① It adopts high-sensitivity balance valve, and the structure layout is changed from horizontal to vertical, and the effect is better.
②A vacuum dehumidification device is installed at the inlet of the sealed oil system.
③Improve the dehumidification effect of the hydrogen dryer.
Measures to improve the effect of hydrogen dryer:
1. Increase the hydrogen flow rate and reduce the humidity at the outlet of the dryer.
2. Uninterrupted operation of the dryer.
3. If the unit is out of service and the generator maintains the hydrogen pressure, the dryer should still be running. The purpose of this: the internal parts of the machine are all in a low temperature state, the sealing oil system is still running, the influent water is still accumulating, and the hydrogen circulation in the machine is stopped. All of these may quickly increase the humidity of hydrogen in the partial space inside the machine near the sealing tile, and it is easy to reach the dew point.
The drying of hydrogen for 300MW generators mainly uses condensing hydrogen dryers. The principle is: a refrigeration device using Freon compressors to create a sealed low-temperature condensing space. When part of the wet hydrogen in the generator passes through this space When the moisture in the wet hydrogen is condensed and condenses into dew, it stays 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 device. The lower the temperature, the better the effect. This factor is related to the power of the refrigeration device, the volume of the space, the flow rate of wet hydrogen, and the temperature. There are certain shortcomings in using this dryer:
1. The outlet temperature of the dryer can only reach -10℃~-20℃, and its drying degree is limited. The heat exchange surface will continue to be frosted, which will increase the thermal resistance and decrease the drying performance. Defrosting heating will cause the dryer to work intermittently and the humidity of hydrogen in the machine will rise. At present, a generator is generally equipped with two hydrogen dryers. It is necessary to check whether the operation mode is correct to ensure that the two dryers operate alternately.
2. The external circulation system has not changed, and it is still driven by the fan pressure difference at the generator end. After the unit is shut down, the problem of losing the drying process in the machine still exists. Therefore, after the power generator is out of service, it should be replaced with air as soon as possible to prevent condensation of hydrogen in the generator.
3. The hydrogen recovery temperature is low (5℃-20℃), and the cold hydrogen temperature in the machine is as high as 40℃. Before the two are mixed, it is completely possible that the stator end windings or the rotor guard ring will be subjected to low temperature continuously for a long time. Infringement, posing a threat to its safe operation.
In view of this phenomenon in the generator, consideration should be given to whether a new type of regenerative adsorption drying system can be used in the selection of hydrogen drying equipment.
If you are interested in diesel generators, please contact us by email firstname.lastname@example.org.
May. 14, 2022
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