Turbine Generator Vibrating on Excitation? How We Found a Rotor Winding Fault Onboard in Sri Lanka
A turbine generator that vibrates heavily every time it is excited is a serious problem, and the cause is often electrical rather than mechanical. Our team attended a vessel at Galle Anchorage, Sri Lanka, to find out why. Three on-site tests showed a grounded main rotor winding with inter-turn short circuits. This update walks through what we tested and what we found, and reflects the work behind our marine electrical services.
Key Takeaways
- The turbine generator vibrated heavily whenever it was excited
- The insulation resistance test read 0 ohms, so the main rotor winding was grounded
- Unequal resistance and uneven voltage drop across the poles showed inter-turn short circuits
- Further excitation testing was not recommended, to avoid more damage
- Rewinding of the main rotor was recommended, followed by full testing before commissioning
What We Were Called In For
Our team of two technicians went onboard to inspect and test the main rotor winding of the turbine generator, after heavy vibration was reported whenever the generator was excited. The troubleshooting was carried out in the presence of the vessel’s technical staff.
The alternator details were:
- Make: ABB
- Voltage rating: 6.6 kV
- Speed: 1800 RPM
- Frequency: 60 Hz
- Number of poles: 4
The Three Tests We Carried Out on the Main Rotor
Vibration that appears only on excitation points to the rotor winding, so we tested it in three steps.
- Insulation resistance (IR) test: carried out at 500 V, the main rotor measured 0 ohms. This confirms the winding was grounded, with insulation failure to earth.
- Milliohm (winding resistance) test: resistance values were unequal across the winding, which indicates a probable inter-turn short circuit.
- Drop test: carried out at 34 VAC and 8.4 A, the test showed an uneven voltage drop across the rotor winding sections, which further confirms inter-turn shorting.
Test Results by Pole
In a healthy rotor, all poles should read almost the same. These readings were not balanced:
| Pole | Resistance | Drop test | Finding |
|---|---|---|---|
| Pole 1 | 0.2116 ohm | 7.6 V | Highest reading |
| Pole 2 | 0.1554 ohm | 4.5 V | Inter-turn short |
| Pole 3 | 0.1560 ohm | 5.0 V | Inter-turn short |
| Pole 4 | 0.1660 ohm | 5.0 V | Inter-turn short |
Poles 2, 3 and 4 read well below pole 1 on both tests. Shorted turns unbalance the magnetic field during excitation, which is the likely cause of the heavy vibration.
Why We Did Not Continue Testing
With the main rotor winding damaged, the AVR (Automatic Voltage Regulator) could not be validated at this stage. We advised against further excitation or operational testing, because running the alternator with a defective winding could make the fault worse and damage the rotor or other turbine generator components.
The AVR and excitation system can be properly checked only after the main rotor has been rewound, followed by the required electrical tests and controlled commissioning of the alternator.
Our Recommendation: Rewind the Main Rotor
The main rotor winding was found to be electrically defective, with a ground fault and inter-turn shorting. We recommended that it be rewound and then tested for:
- Insulation resistance
- Winding resistance
- Electrical balance
These checks are done before reassembly and commissioning of the turbine generator. The findings were shared with the vessel’s technical staff and a full service report was submitted. For similar work on motors and generators, see our motor rewinding and repair service.
Why It Matters for Ship Operators
Simple electrical tests separate winding faults from mechanical ones quickly, so owners can plan repairs and spares with a clear report in hand. Parts and materials for the repair can be arranged through our marine spare parts supply.
Have your generator checked if you notice:
- Heavy vibration when the generator is excited or loaded
- Unstable voltage or unusual readings
- Low insulation resistance or tripping on earth fault
More Marine and Industrial Services
Alongside this job, we support vessels and plants with:
- Marine electrical services
- Marine welding and fabrication
- Marine mechanical service
- Marine hydraulics
- Governors, fuel pump and injectors
- Navigation and communication
- Marine spare parts suppliers
- Automation
- HVAC and refrigeration
- LSA and FFA
- Motor rewinding and repair
Generator vibrating or tripping on earth fault? Send us the vessel and equipment details and we will advise on the right next step, whether it is onboard a vessel or in your plant. Learn more on our marine electrical services page.
📞 +971 4 576 2560 |
✉ info@mi-solutions.in |
Get a Free Quote →