What is the appropriate size of the air inlet of a diesel generator?
What is the appropriate size of the air inlet of a diesel generator?
Calculate the air duct according to the cooling air volume provided by the diesel generator, the cross-sectional area of the air duct × the wind speed = the air volume, so the lower the wind speed, the larger the cross-sectional area, take a balance between the two, and then check the air pressure, according to the air duct resistance table Calculate the air pressure from the air inlet to the cooling extension. The calculation method is the air pressure of the fan – the resistance of the air duct. If the air pressure will be too much (the air duct is too long), you need to increase the cross-sectional area of the air duct to reduce the resistance. Consider adding an additional fan. The exhaust air is calculated according to the air intake volume, because the heated air volume is relatively large, if the air duct is too long, it is necessary to increase the air duct volume, which can generally be selected according to 1.2 times the air intake volume.
Furthermore, the size of the air inlet of the diesel generator set should be 25% larger than the effective area of the diesel generator water tank.
What are the maintenance and precautions for marine generator sets?
Most marine 50Hz or 60Hz alternators are three-phase synchronous generators. According to the engine, it can be divided into three types: gas generator, steam turbine generator and diesel generator. On some large ships and some ships, steam turbine generators or gas turbine generators are used. Most ships use medium-speed diesel generators. Other ships use low-speed shaft generators, mostly medium-sized.
In order to ensure the normal operation of the generator, there should be no accumulation of water, oil and dirt near it, and no corrosive gas, so as not to damage the insulation of the generator winding.
While preventing moisture and dust, be careful not to affect the normal ventilation and cooling of the generator. Always clean the dust and dirt in the ventilation holes to keep them unobstructed. The temperature of the cooling air should not be too low to avoid condensation on the windings and other conductive parts.
For generators that stop running for a short time for some reason, the collector ring does not need to be wrapped for protection, but insulating cardboard, paraffin paper or asphalt paper should be padded between the brush and the collector ring to prevent the brush from being on the surface of the collector ring— spots are formed.
If the machined surface of the generator is rusted due to oil or paint peeling off, it should be removed in time and painted with anti-rust paint.
The disassembly method of the generator is roughly the same as that of the asynchronous motor, but due to the heavy weight of the generator, care should be taken not to bruise it during disassembly. When removing the end cover, be careful not to damage the stator coil protruding from the surface of the machine base; when taking out the rotor, put cardboard between the stator and rotor of the motor to prevent damage to the iron core and winding. When tying the rotor with steel cables, The wire rope must not touch the rotor journal, fan, collector slip and lead wire of the hand. The place where the wire ropes are tied must be padded with wooden boards or rubbers.
The newly installed synchronous generator should generally be dried before running. If the insulation resistance meets the requirements, drying may not be carried out, but the load within 24h of the start of operation is very good and does not exceed 50% of the rated capacity.
When the generator in operation is stopped for maintenance or the out-of-service time exceeds the specified limit, and the insulation resistance is lower than the specified value, it must be dried. If it is determined that the surface is damp, it can be dried with a load drying method.
There are many methods of drying, the following methods can be used on ships:
(1) Hot air method: blow the dry and clean waste hot air generated by the main engine into the generator to dry the stator and rotor windings. To prevent the shaft from being deformed, the rotor should be rotated 180 degrees periodically. When drying, the winding surface temperature should be controlled. Measured with a thermometer, the surface of the winding should not exceed 85°C, and the air temperature at the air inlet should not exceed 90°C.
(2) Short-circuit current drying method: short-circuit the output end of the generator through an ammeter to adjust the rotor excitation current so that the current of each phase of the stator is 50-70% of the rated current. The generator can run off rated speed, but the speed should be kept constant to avoid temperature instability.
The short-circuit point is preferably selected at the stator lead-out end, or it can be short-circuited through the transformer and dried together with the transformer.
This method dries the stator and rotor windings at the same time.
(3) Load drying method: If the marine generator is only wet on the surface, it can be dried with load drying method. When dry, the generator can run with 50% rated current load first. Then press 65%, 85%, 100% value to increase to rated current. Each level of load runs for 24h. During the drying process, the insulation resistance of each winding should be measured regularly.
Precautions when drying;
Heating and drying should be carried out in clean air, and the generator should be blown clean with compressed air before drying.
If the winding is seriously wet, it needs to be dried with hot air first, and then dried with load after a certain period of time to avoid insulation breakdown.
When drying, more thermometers should be placed and distributed in each part of the generator, so as to grasp the temperature of each part and prevent local overheating.
Heating should be carried out slowly to avoid insulation damage due to sudden evaporation of moisture inside the coil. If the drying temperature does not reach the required temperature, drying can be carried out at a slightly lower temperature, but the time should be appropriately extended.
In the early stage of generator drying, due to the heating of the windings and the evaporation of water, the insulation resistance drops, and then gradually rises. The rising speed becomes slower and slower, and finally stabilizes at a certain value. At a constant temperature, when the insulation resistance remains unchanged for more than 3 hours, the drying work can be completed.
Regardless of the method, after drying, when the coil is cooled to 60°C, the absolute resistance of the stator winding and the rotor winding is measured with a 500V megohmmeter and should not be less than 0.5M ohms.
(4) Maintenance and maintenance of diesel generator bearings
In the sliding bearing lubricated by the oil ring, the amount of oil in the bearing should be constant, and it is generally not filled with oil during operation. When the amount of oil is below the specified liquid level, the bearing should not throw oil to avoid splashing on the windings.
Motors with ball or roller bearings need to be replaced once when running for about 2000 hours. When the bearing is used in a dusty and humid environment, the lubricating oil should be changed frequently according to the situation.
Before starting a generator that has been out of use for a long time: if a rolling bearing is installed, its lubrication state must be checked first. If the original grease is dirty or hardened and deteriorated, the bearing must be rinsed first, and then cleaned with gasoline. Fill with clean grease very late. The filling amount is 2/3 of the bearing chamber space, and it is not allowed to fill too much.
(5) Maintenance of slip rings and brushes
The surface of the slip ring should remain smooth and cylindrical. If the surface has patina and burn marks, it should be ground with 00 fine abrasive cloth. When grinding, the abrasive cloth should be installed on the curved shingle with a diameter suitable for the slip ring. Grinding on the fly is also possible.
If the surface is seriously burnt or the collector ring is deformed, a light car should be carried out, and the light car can be carried out when the ship enters the factory for maintenance.
To make the slip ring wear evenly, its polarity must be changed once or twice a year.
Brushes are easily damaged parts and should be checked frequently.
- Check the inside of the generator carefully, there must be no debris, and prevent foreign objects such as screws, tools, and rags from falling into it.
- Remove dust from all parts of the generator with dry compressed air or a leather tiger at about two atmospheres. To avoid damage to the coil, metal blowpipes must not be used.
- Check the lubrication of the generator bearings. The quality and quantity of oil and grease must comply with maintenance requirements.
- Check that the connection between the generator and its prime mover is in good condition. At the same time, check whether the axes of the two machines are on the same straight line.
- Check whether the rotor is flexible, and check the bearing quality.
- Clean the collector rings.
- Check the brush device; the brush pressure is 14.7-19.6kPa.
- To measure the insulation resistance, use a 500V megohmmeter to measure not less than 0.5M ohms.
