Maintenance and debugging of seawater flooded diesel generators
In marine voyages, the crew's accidental and incorrect operation, poor communication, and failure of mechanical equipment can cause damage to the ship's diesel generator set . Marine diesel generator sets, also known as marine auxiliary engines, provide power for lighting, communication, control, air conditioning, ventilation, ballasting, cargo barge and other equipment for the entire ship. A single-point mooring FSO (Floating Storage and Offloading Device) wheel during this maintenance was due to the crew's operation errors during production, and due to the bad sea conditions at that time, a large amount of water entered the engine room, causing engine room machinery. The control room and below were flooded with seawater. Taking into account the age of the ship, the working life of related equipment and economic factors, the shipowner decided to repair the diesel generator set. Different from the maintenance of conventional diesel generator sets, the diesel generator set submerged in seawater must be disassembled to the part level, and all mechanical parts, electronic components and sensors must be thoroughly cleaned and inspected. However, if most of the mechanical and electrical functions can be restored after cleaning and repair, it can also produce greater economic benefits. The measured data after commissioning and repair can also provide a reference for related design and maintenance personnel. 1 Overview of seawater flooded diesel generator sets The diesel engine model in this round of seawater flooded generator sets is D ai & shy; hatsu 6DS-26, and the generator model M itsu bishi ccc. Both the diesel engine and generator were produced in 1974 and have a long age. The diesel engine is a 6-cylinder four-stroke diesel engine with a maximum speed of 720 r / min and a rated power of 750 kW. The rated power of the generator is 937.5 k V .A, the rated voltage is 450 V, the rated current is 1023 A, the excitation voltage at full load is 48 V, the excitation current is 6.4 A, and the power factor is 0.8. The rated speed of the generator is the same as the rated speed of the diesel engine. The seawater poured into the cabin completely submerged the generator set. The ship was towed to Youlian Shipyard (Shekou) Co., Ltd. for maintenance by tugboat in March 2017. When entering the ship, the engine room was cleaned and the construction conditions were met. 2 Diesel Engine Maintenance Clean the exterior of the diesel engine before disassembling it. First, mark and dismantle related pipes and filters such as fuel oil, lubricating oil pipes, seawater cooling water, fresh water cooling water, intake air, and exhaust smoke of diesel engines, and remove measurement and control systems such as temperature, pressure alarm sensors, and instrument lines. Next, remove the cylinder head, crank out the piston, crank connecting rod, and replace with a new cylinder liner. Lift the cylinder block, disassemble the crankshaft bearing and lift out the crankshaft, and then thoroughly clean the oil pan. After disassembly and cleaning, perform corresponding maintenance and measurement according to the condition of the parts. During maintenance, key parts such as pistons and piston rings, cylinder liners, connecting rods and connecting rod bolts, and connecting rod pads are measured and repaired. Inspection found that all journals of the crankshaft were corroded and had pull marks. Because the cost of renewing the crankshaft is too high, it can only be repaired by contacting an external contractor. Service providers who repair marine equipment should obtain the formal approval of the relevant classification society, and those who provide parts should also obtain the product approval of the classification society. A surveyor from a classification society should be engaged in the repair process for inspection. The shipyard and maintenance project team chose Dalian Dongshi Beryllium Iron Co., Ltd. for maintenance. After maintenance, the outer diameter of the crankshaft journal, the runout of the main journal, the radial runout of the flange, and the end-face runout, the parallelism of the crank neck and the axis of the main shaft journal, and the crank arm distance differences all reached the standard. After the repair, after the CDX-II electromagnetic yoke flaw detector is inspected and the dynamic balance is checked, it is confirmed that the crankshaft repair is qualified and can be reinstalled. The diesel engine gas distribution mechanism has also been dismantled and measured. The intake and exhaust valves and valve seats are repaired and ground; the rocker arm mechanism and valve spring are all disassembled and inspected. This type of cam lifting mechanism for intake, exhaust and fuel injection timing is all done on one camshaft (Figure 1). Opening each door, you can see that the two cams control the intake and exhaust respectively, and the other cam controls the action of the fuel injection mechanism. After inspection, the camshaft cam size and wear did not exceed the limit, and the camshaft bending, deflection, and torsional deformation did not exceed the limit range. You can continue to Figure 1 Diesel generator gas distribution mechanism (partial) Edge jealousy and repair equipment management and group Meal 129 used. However, this design has very high requirements on the material of the camshaft, the design of the firing sequence, the processing technology, and load distribution, and once a cam fails, the entire camshaft will be scrapped. Therefore, although this design can save space and reduce the number of institutions, it is still not suitable. This is why modern diesel engines mostly use two camshafts to control intake, exhaust and fuel injection. When refitting a diesel engine, attention should be paid to controlling the assembly accuracy, such as the flatness of the surface of the base and the casing, the clearance between the piston ring and the cylinder liner, the clearance between the valve and the valve seat, and checking the cooperation of the cooperation mechanism to ensure that they are properly matched Such as the cooperation of camshaft with ejector rod and rocker arm. When reinstalling the diesel engine, avoid leaving pollutants, tools, and parts inside the diesel engine. After assembly, it should be manually cranked and checked to confirm the installation status. 3 Generator set maintenance According to the site conditions, determine the main stator, main rotor, exciter stator, bearing pads, main junction box, rotor bearing position, end cover bearing room and other parts. After removing the excitation stator, wipe the shaft with alcohol, and measure the diameter and the bearing wear of the generator drive shaft end and non-drive shaft end. The measured bearing wear does not exceed the standard, and can be used continuously. After the test, the generator stator winding, the main rotor, the excitation stator winding insulation part and the generator parts are cleaned thoroughly with a motor-specific cleaning agent until the true color is exposed. Brush the hard-shelled parts repeatedly with a brush, and use the soaking process on the particularly dirty parts. Put the motor in clean water, add motor cleaning agent to heat to 100 ° C for 24 hours, and completely remove the salt from the motor to improve the insulation effect. After cleaning, hang the motor into the oven to dry. After drying, immerse the motor with H-level insulation paint. Because the curing temperature of the solvent-free insulating paint used by the motor is (145 ± 5) yi, and the operating temperature of the motor generally does not exceed 105 yi (setting the ambient temperature of the cabin to 40 yi). In order to avoid affecting the life of the motor, it was decided to pre-bake in the oven for 8 hours and then vacuum-dip the paint out of the oven, and then dry in the oven for 18 hours. The surface of the motor rotor and other parts should be sprayed with anti-rust paint. Turn the lathe on the generator's rotor to verify the bending of the shaft and correct it to pass, and then perform a dynamic balance test. After the generator is assembled, relevant tests such as AC withstand voltage, DC leakage test, no-load test, temperature rise test, vibration test should be performed. 4 Preparatory work before commissioning of diesel generator set After completing the repair of the diesel engine and generator, the corresponding preparation work should be done before commissioning. First reinstall the diesel engine and generator and connect them. During the reassembly, attention should be paid to the mechanical installation precision control such as the coaxiality of the two machines, the flatness of the base, and the tightness of the coupling. Before commissioning, check and confirm that the diesel engine intake and exhaust pipelines, fuel pipelines, lubricating oil pipelines, seawater and freshwater cooling pipelines, high-pressure gas pipelines for rushing cars, security alarms, and parking systems are restored. Electrically, the phase sequence of the wiring between the generator set and the main power distribution board should be checked, the excitation wiring is correct, the excitation AVR control board is valid and the direction of the residual magnetic field is confirmed, and the brine tank is prepared to be used as a load. 5 After the preparations for the no-load running-in test of the diesel engine are completed, the commissioning can begin. Run the no-load running-in test of the diesel engine according to the pre-programmed debugging procedure. Before the no-load test, the fuel, lubricating oil, seawater and fresh water cooling systems should be run first, and it should be confirmed that they meet the working pressure requirements to ensure that the bearings, pistons, and swing arms are fully lubricated and the cooling system can work normally. Avoid damage to the machine due to blocked pipes or filters. In the no-load test, the diesel engine only drags the generator rotor to idling, neither is it connected to the excitation, and the main circuit of the generator is not explained. Start jogging the car first and confirm that the high-pressure gas line can be closed after starting. After the diesel engine is started, use the governor to set the speed to 400 r / min, and run in sequence of 5 min, 10 min, and 30 min. During each operation, check whether the fuel, lubricating oil, cooling system pressure, and temperature meet the standards, and the inlet and exhaust temperatures of each cylinder, and record the relevant data. After each run, open the door to measure the bearing and crankpin temperature. If the diesel engine runs stably without obvious vibration, the speed can be increased. In this test, the subsequent speeds were set to 450 r / m in, 720 r / m in and 30 m in respectively. Open the crankcase immediately after each stop, check the main bearing, crank pin bearing temperature and motor bearing temperature, whether the gear pair has sufficient lubricant and the condition of each fastener, especially check whether the connecting rod fastening bolt insurance is complete, and Manually crank for more than 2 weeks to check for abnormalities. During the running-in test, if there are abnormalities such as knocking, high temperature, and low pressure, the machine must be stopped and inspected in time to pass the above tests. If the diesel engine is operating normally, subsequent commissioning can be performed. 6 After the commissioning of a single diesel generator and the running-in test of a parallel diesel engine, the single machine with load can be commissioned. Because this commissioning generator set has a long working life, it cannot be tested in accordance with the new classification rules of the ship classification society ABS (American Bureau of Shipping). In order to ensure the normal operation of the unit, commissioning steps were determined according to the needs of production operations. Diesel engines have a rated power of 720 kW and a rated speed of 720 r / min. During commissioning: 107 k W, 720 r / min in operation 120 m in; 190 k W, 720 r / m in operation 30 m in; 260 k W, 720 r / m in operation 30 m in; 373 k W The test was performed at 720 r / min in 90 min, 402 kW, and 720 r / min in 30 min. Each test records the cooling water outlet temperature, fuel pressure, cooling seawater / fresh water pressure, bearing, piston, rocker oil pressure, lubricating oil temperature, exhaust turbocharger inlet temperature, and turbocharger speed Air temperature and oil pump rack position. During power 402 kW experiments, the explosion pressure and compression pressure were measured. After the 402 kW test, the main bearing and connecting rod shoe temperatures were measured. For the generator, record the voltage, current, active power, reactive power, and power factor active power, reactive power, frequency, excitation voltage and excitation current, and motor temperature rise of the corresponding load. Before the diesel generators are put into production, they should also undergo security tests. Make sure that the security functions of lubricating oil, fuel oil, and cooling water are low, high-temperature parking, and flying stop are normally implemented. In this test, the actual pressure of lubricating oil, fuel oil, and cooling water is low, and the high-temperature parking and flying stop are simulated tests. After passing the test, they are restored to the standard settings in accordance with the instructions of the auxiliary machine. In the parallel test, the active power and reactive power difference of the parallel generator should also be recorded. After the car is connected and after the car is connected, you should always pay attention to whether the voltage difference, current difference, and frequency difference of the parallel generator are exceeded, and deal with the abnormal situation in time. 7 Delivery of generator sets After no-load running-in test and parallel test, diesel generator sets can be delivered to the ship. In use, the various data of unit operation should be paid equal attention. After this repair, the function of the three generator sets of the ship was basically restored, which helped the shipowner greatly save the maintenance costs, and was well received by the shipowner and the project team. At the same time, the staff involved in the repair accumulated a wealth of marine submerged equipment. Maintenance experience.