1. Mechanical Power System Inspection
(1) Verify Engine Speed
Use a mechanical tachometer to measure the diesel engine’s flywheel speed and ensure it reaches the generator’s rated speed (typically 1500/1800 rpm). Focus on checking if the electronic governor’s actuator is stuck or malfunctioning, and whether the fuel injection system is functioning properly.
Case Example: At a cement plant, poor atomization of the fuel injectors caused speed fluctuations of ±200 rpm, leading to intermittent voltage output.
2. Electromagnetic System Diagnosis
(2) Residual Magnetism Recovery
Disconnect the excitation circuit and briefly connect a 12V battery to the excitation winding (be mindful of polarity).
Case Example: A marine generator set, after long-term disuse, had residual magnetism lower than 0.3V. After DC magnetization, the output voltage recovered to 80% of rated voltage.
3. Circuit System Inspection
(3) Rotating Rectifier Test
Use an insulation resistance tester to measure the forward resistance of the rotating diodes (normal value is 0.3-0.7Ω). The reverse resistance should be >100kΩ.
Case Example: A generator set had an issue with the rectifier bridge where poor heat dissipation caused a PN junction breakdown, leading to an abnormal increase of 30% in excitation current.
4. Control System Fault Diagnosis
(4) AVR Module Dynamic Testing
Measure the excitation output voltage at the rated speed; it should be within the range of 40-80V DC.
Case Example: A backup power system at a hospital failed due to the AVR’s voltage regulator tube malfunctioning. This caused the excitation voltage to fluctuate by ±15V. Replacing the AVR restored stable voltage output.
5. Winding Integrity Inspection
(5) Three-Phase Winding Insulation Test
Use a 2500V megohmmeter to measure the stator winding’s insulation resistance to ground. New generators should have a resistance >100MΩ, and running generators should have a resistance >5MΩ.
Case Example: During maintenance at a hydroelectric plant, it was found that carbon dust accumulation on the winding surface reduced insulation resistance to 0.5MΩ. After cleaning, the insulation value returned to normal.
6. Special Operating Conditions
(6) Harmonic Distortion Mitigation
When the load includes a large number of frequency converters, it is recommended to install a 12-pulse rectifier unit.
Case Example: After installation, a data center saw the voltage waveform distortion rate drop from 15% to 3%, meeting the IEC 60034 standard requirements.
Fault Tree Analysis
80% of no-voltage failures are concentrated in the excitation system (including AVR and rotating rectifiers), 15% are due to mechanical drive issues, and 5% are caused by winding damage.
Recommended Maintenance Schedule:
- Routine Inspections: Every 8 hours
- Preventive Maintenance: Every 500 hours
- Overhaul: Every 10,000 hours
This approach can reduce failure rates by more than 70%.