Industry News

Daily maintenance and maintenance of marine generators

Marine 50Hz or 60Hz alternators are mostly three-phase synchronous generators. The generator components are three kinds of gas generators, steam turbine generators and diesel generators. Most large ships or ships use turbo generators or gas turbine generators. The usual ships use medium speed diesel generators. Some ships also use low-speed shaft generators, mostly medium-sized.

1. General maintenance
In order to ensure the normal operation of the generator, there should be no water, oil and dirt accumulation near it, and there should be no corrosive gas to avoid damage to the generator winding insulation.
At the same time of moisture and dust prevention, care must be taken not to affect the normal ventilation and cooling of the generator. Always clean the dust and dirt in the ventilation ducts and keep them unobstructed. The temperature of the cooling air must not be too low to prevent condensation on the windings and other conductive devices.
For generators that have stopped running for a short time, the collector ring does not need to be wrapped and protected, but it should be insulated with cardboard, paraffin or asphalt paper between the brush and the collector ring to prevent the brush from being on the surface of the collector ring— Spots are formed on it.
If the machined surface of the generator is rusted due to oil and paint falling off, it should be derusted in time and coated with anti-rust paint.

2. Disassembly precautions
The generator disassembly method is almost the same as that of the asynchronous motor, but due to the large weight of the generator, care should be taken not to damage the disassembly. When disassembling the end cap, be careful not to damage the stator coil protruding from the surface of the base; when removing the rotor, use a cardboard between the stator and the rotor to prevent damage to the iron core and the winding when the rotor is tied with the cable. The cable should not touch the rotor journal, the phoenix fan, the collector slip and the hand-lead. The ropes must be padded with wood or rubber.

3. Generator drying
Newly installed synchronous generators should generally be dried before operation. If the insulation resistance meets the requirements, the drying may not be performed, but the load within 24 hours of the start of the operation preferably does not exceed 50% of the rated capacity.
When the running generator is shut down for maintenance or deactivation beyond 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 by a load drying method.
There are many ways to dry, and the following methods can be used on ships:
(1) Hot air method: The dry and clean waste hot air generated by the main unit is blown into the generator, and the stator and rotor windings are dried. To prevent deformation of the shaft, the rotor should be rotated through 180 degrees periodically. When drying, the surface temperature of the winding should be controlled. With a thermometer, the surface of the winding must not exceed 85 ° C, and the air temperature at the air inlet must not exceed 90 degrees.
(2) Short-circuit current drying method: short-circuit the generator output terminal through the ammeter to adjust the rotor excitation current so that the current per phase of the stator is 50-70% of the rated current. The generator may not operate at the rated speed, but the speed should be kept constant to avoid temperature instability.
The short contact point is preferably selected at the stator lead-out end, or it can be short-circuited by a transformer and dried together with the transformer.
This method can dry both the stator and the hand winding.
(3) Drying method with load: If the marine generator is only wet on the surface, it can be dried by the method of drying with load. When dry, the generator can be operated with a 50% rated current load. Then increase the rated current by 65%, 85%, and 100%. Each level of load runs for 24h. The insulation resistance of each winding should be measured periodically during the drying process.
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 wet, it needs to be dried by hot air method. After drying for a certain period of time, it is dried with load to prevent the insulation from being broken down.
When drying, put more thermometers on each part of the generator to keep the temperature of each part to prevent local overheating.
Heating should be carried out slowly to avoid the insulation damage caused by the 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 lengthened.
In the initial stage of generator drying, as the winding heats up, the water evaporates and extracts, so that the insulation resistance decreases, and then gradually rises, the rising speed becomes slower and slower, and finally stabilizes at a certain value. At a constant temperature, the drying operation is completed when the insulation resistance is maintained for more than 3 hours.
Regardless of the method, after drying, when the coil is cooled to 60 ° C, the stator resistance of the stator winding and the hand winding is measured with a 500 V megger and should not be less than 0.5 MΩ.

4. Maintenance and maintenance of generator bearings
In oil ring lubricated plain bearings, the amount of oil in the bearing should be constant, and it is generally not oiled during operation. The oil quantity is below the specified liquid level, and the bearing should not be oiled to avoid splashing on the winding.
For motors with ball or roller bearings, the grease needs to be replaced once when it is running for about 2000 hours. When the bearing is used in a dusty and humid environment, the lubricant should be changed frequently depending on the situation.
Before starting the generator that has been deactivated for a long time: If the rolling bearing is installed, the lubrication state must be checked first. If the original grease is dirty or has hardened and deteriorated, the bearing must be washed first and then cleaned with gasoline. Finally fill in the clean grease. The filling amount is 2/3 of the space of the bearing chamber, and it should not be filled too much.

5. Collector ring and brush maintenance
The surface of the collector ring should be smooth and cylindrical. If the surface has patina and burn marks, grind it with a fine sand cloth No. 00. When grinding, the abrasive cloth should be placed on a curved wooden tile whose diameter is compatible with the slip ring. It can also be ground in operation.
If the surface is seriously burned or the collector ring is deformed, the light car should be carried out, and the light car can be carried out when the ship enters the factory for inspection. In order to make the collector ring wear evenly, its polarity must be changed once or twice a year.
Brushes are easily damaged parts and should be checked frequently
1. Look carefully at the inside of the generator, and there must be no debris to prevent falling into screws, tools, rags and other foreign objects.
2. Use approximately 2 atmospheres of dry compressed air or a skin tiger to remove dust from various parts of the generator. To avoid damage to the coil, do not use a metal blow tube.
3. Check the lubrication of the generator bearings. The quality and quantity of lubricants and greases must meet the maintenance requirements.
4. Check that the connection between the generator and its prime mover is good. Also check if the axes of the two machines are on the same line.
5. Check the rotor for flexibility and check the bearing quality.
6. Clean the slip ring.
7. Check the brush unit; the brush pressure is 14.7 to 19.6 kPa.
8. Measure the insulation resistance and measure it with a 500V megohmmeter of not less than 0.5M ohms.