Q1: We have several diesel generator sets that have been in operation for ten years, and power output has dropped significantly recently. The repair shop recommends an overhaul. What exactly does an overhaul include? How long will it last after the overhaul?
A: Generator engine overhaul is not simply replacing parts; it is a complete restorative process. First, the engine must be removed from the generator set and completely disassembled into individual components. The cylinder block must be measured on an inspection stand for bore roundness and cylindricity. If wear exceeds limits, a cylinder boring machine is used to restore roundness, and oversized pistons are fitted. The crankshaft must be measured for journal wear and straightness, reground on a crankshaft grinding machine to restore precision, and fitted with undersized bearings. Wear-prone parts such as piston rings, connecting rod bearings, main bearings, front and rear oil seals, cylinder head gaskets, intake and exhaust valves, and valve stem seals must all be replaced with new ones regardless of their condition. After full assembly, the engine must undergo load testing on a dynamometer, and only when power output, fuel consumption, exhaust temperature, and smoke opacity all meet specifications can it be released. The cost of a generator engine overhaul is about 40% of the price of a new unit. After overhaul, performance can be restored to over 90% of a new unit, and with normal use and maintenance, it can last another six to eight years. In Hainan, when enterprises with bonded maintenance qualification perform engine overhauls, the imported piston rings, bearings, and other needed parts can enter duty-free, and the procurement cycle is compressed from two to three months to one to two weeks.
Q2: Our daily engine maintenance mainly consists of changing the oil and filters. Is this sufficient? What else needs to be done?
A: Diesel engine repair services cannot stop at just changing the oil. The correct approach is tiered maintenance based on operating hours. At 250 hours, change the oil, oil filter, and fuel filter, clean the air filter with low-pressure air from the inside out, and check belt tension. This is basic maintenance to ensure lubrication and cleanliness. At 500 hours, in addition to the first-tier maintenance, also check valve clearance (standard: intake valves 0.25–0.30 mm, exhaust valves 0.30–0.35 mm—adjust if deviation is large); check fuel injector atomization quality—clean or replace if poor; check turbocharger impeller clearance—rotate the impeller by hand to feel for binding. At 1,000 hours, in addition to the second-tier maintenance, also measure cylinder compression pressure with a compression gauge (normal range: 2.5–3.0 MPa, pressure difference between cylinders not exceeding 8%); check crankshaft end play (standard: 0.10–0.30 mm); and check connecting rod bearing clearance. The essence of tiered diesel engine repair services is using small, distributed investments to avoid large, concentrated expenditures. Each tier has a clear purpose. Skipping any tier means missing the problems that tier would have detected.
Q3: Our generator suddenly stopped producing power, and our electrician couldn't find the cause after checking for a long time. Where should we start troubleshooting in this situation?
A: The worst approach in generator troubleshooting is to disassemble the windings immediately. The correct sequence is from simple to complex, from high probability to low probability. Step one: open the protective cover and check the carbon brushes. Any brush shorter than 10 mm must be replaced. Also check the slip ring surface—if there is an oxide film or burn marks, polish it with fine sandpaper. These two steps resolve about 30% of faults. Step two: check residual magnetism. Self-excited generators rely on residual magnetism to establish initial voltage. After long-term shutdown, residual magnetism may disappear. Use a 12-volt battery to briefly energize the excitation winding for two to three seconds to remagnetize it. Step three: use a multimeter in diode test mode to test the rotating rectifier diodes. A normal diode conducts in one direction and blocks in the reverse. If faulty diodes are found, replace them in complete sets. Step four: check the automatic voltage regulator—check whether the fuse is blown, whether the indicator light is on, and whether the potentiometer is oxidized. Step five: only then consider the stator windings. Following this generator troubleshooting sequence, most failure-to-energize issues are resolved within the first few steps without ever needing to touch the windings. In Hainan, enterprises with bonded maintenance qualification can quickly source the imported carbon brushes, rectifier diodes, and AVRs identified as needing replacement during troubleshooting.
Q4: We hire someone to perform generator testing once a year, but we don't really understand the data on the test reports. Which data are most important? How do we determine whether the equipment is in good condition?
A: Generator performance testing focuses on three key indicators. The first is insulation resistance. Use a 500-volt megohmmeter to measure stator winding-to-ground resistance. In cold condition, it should be greater than 5 MΩ; in hot condition, greater than 1 MΩ. If this value is continuously decreasing, the windings are absorbing moisture or aging, and maintenance should be scheduled. The second is three-phase DC resistance. Use a bridge meter to measure the DC resistance of the three-phase windings. The deviation among the three values should not exceed 2%. An increasing deviation may indicate inter-turn short circuits or poor connections in the windings. The third is voltage regulation. From no load to full load applied incrementally, voltage variation should be less than ±2.5%. Exceeding this range indicates problems with the excitation system or automatic voltage regulator. A single test data point only indicates the current condition. Comparing multiple test data points reveals trends. Store each set of generator performance testing data. If insulation resistance has been declining for three consecutive months, maintenance should be scheduled. If voltage regulation suddenly increases, the excitation system should be inspected. Data does not lie, and trends are more important than single values.
Q5: We want to establish a standardized maintenance system, but we don't know which items to inspect. Is there a standard checklist we can reference?
A: A generator maintenance checklist can be organized by time period. Daily items: check fuel level, oil level, and coolant level; check battery voltage (12V system not less than 10V, 24V system not less than 20V); check terminal connections for looseness. Items to observe during operation: exhaust color (colorless or light gray is normal; black, blue, or white smoke all indicate problems); whether operating sounds are even; whether voltage and frequency are stable; whether oil pressure and coolant temperature readings are within normal ranges. Every 250 operating hours: change oil and oil filter, change fuel filter, clean air filter, check belt tension. Every 500 operating hours: check valve clearance, check fuel injector atomization quality, check turbocharger clearance, check coolant quality. Every 1,000 operating hours: measure cylinder compression pressure, check crankshaft end play, check bearing clearance. Print out this generator maintenance checklist and post it in the generator room. Perform tasks when scheduled, check them off when completed—do not rely on memory.
Q6: We are familiar with engine repair, but what does generator repair itself include? How is it different from engine repair?
A: Diesel engine repair services are different from generator repair, as the latter focuses more on electrical components. Engine repair focuses on mechanical components such as cylinder blocks, crankshafts, pistons, and bearings, addressing issues like power output, fuel consumption, and starting. Generator repair focuses on electrical components such as stators, rotors, excitation systems, and AVRs, addressing issues like voltage, frequency, and insulation. Daily generator repair includes: carbon brush inspection and replacement (replace when length is less than 10 mm), slip ring surface polishing (when oxide film or burn marks are present), rotating rectifier diode testing (use a multimeter in diode test mode; if faulty diodes are found, replace them in complete sets), AVR calibration (check fuse, indicator light, potentiometer), and winding insulation testing (regular measurement with a megohmmeter). Generator overhaul includes: stator winding rewinding or repair, rotor excitation winding repair, bearing replacement, and complete cleaning, varnishing, drying, and testing of the generator. Generator repair and engine repair are two different technical systems. A good service provider should be proficient in both.
From overhauls to daily maintenance, from fault diagnosis to performance testing, from checklists to electrical repairs—a complete equipment maintenance system must cover both the engine and generator domains. The bonded maintenance policy in China's Hainan Free Trade Port gives qualified enterprises an advantage in importing parts. If you are seeking a more reliable solution for your power plant's equipment maintenance, professional technical support can help you reduce maintenance costs, shorten equipment downtime, and ensure the long-term reliability of your equipment.