A while ago we have experienced frequent black outs due one of the vessel’s generators trip while running on load. The generator used to trip if load went more than 50 % while was running as a single generator and especially when a large consumer starts when the generator was close to 50 % load. The alarm showed on alarm monitoring system was “Generator trip” and when checked on generator local panel located inside high voltage (HV) room the alarm found to be “Underfrequency alarm”.
Generator frequency is the number of electrical cycles per second, measured in Hertz (Hz) and this is directly proportional to the engine speed. So if the frequency goes down, it is due to the engine speed drop while on load and the most frequent cause of it is engine fuel starvation. If the generator frequency drops but the engine speed is constant, then its a different problem which is related to engine control, safety and automation.
So, there are few different reasons which can trigger this kind of problem:
- fuel starvation (fuel supply pump failure, fuel filter blockage etc.)
- poor performance of one of the engine units
- fuel injection pump failure on one of the units
- poor combustion due air supply restriction
- engine governor failure
- current transformers failure
- engine control and safety system failure
In our situation we noticed that the engine rpm dropped before generator trip and we have started troubleshooting by checking the following:
- the whole fuel supply system and found it in good condition.
- the engine performance and found it in fairly good condition at present load, with all units properly balanced.
- checked the governor setting and found similar or close to all other generators.
So, we were a bit confused and decided to replace the governor, Europa type, as we thought that it might be a problem with it of being sluggish at high engine load but…we were wrong. Even with the new governor the engine behaves the same without being able to run beyond 50 % load.
If there is a fault into the governor the quality of control deteriorates and become unstable. Most of the operating faults result from: dirty injection pump fuel linkage, excessive play in the bearings of the fuel control shaft, sluggish fuel control shaft, worn ball joint heads, excessive play between governor output shaft and the fuel control shaft, failure to comply with the intervals for changing the governor oil, failure to comply with the required intervals for maintaining the governor, faulty connectors and cables.
As a result we decided to monitor closely the engine behavior while we were load it up and learned that actually, when the engine was running at 50 % load the fuel pump’s racks were fully in and governor was unable to push them further inside when engine load required. It seems that someone, adjusted the fuel racks in order to balance the engine units without checking fuel injection timing and without checking and re-adjusting the engine governor linkage accordingly.
Fuel control linkages transfer the rotation of governor terminal shaft to move the fuel rack in order to control quantity of fuel injection by governor.
Though the fuel control linkages were adjusted and fixed by the governor’s maker before delivery, the movement of the governor terminal shaft and fuel racks should be checked before engine starting and during operation.
So we have re-adjusted the engine governor and fuel racks and after we have tested the engine at full load with no other further issues.
The procedure for adjusting the linkage and fuel rack on a MAN engine, 32/40 type is as follow:
- with governor at 0 % load the fuel racks should be set @ 0 mm.
- with governor at position 8 (100 %) load, the fuel racks should be set to approx. 36 mm.
The procedure of adjusting the Europa type governor for generator’s auto synchronizing is as follow:
- The power supply for e-motor should be checked and adjusted to 20 VDC – 24 VDC. This can be done from the remote governor speed controller by slowly turning the potentiometer from the PCB.
- Make sure that all governors are adjusted to the same proportional factor (P°).
- Open restrictor screw 1/2 to 3/4 turns. Be very careful in closing restrictor screw (by hand only) because the screw is very sensible.
- Two generators must be on AUTO mode with equal load sharing.
- Switch both generators on MANUAL mode.
- Switch on a big consumer and check generator’s load distribution.
- Generator with higher load P° must be increased. Generator with lower load P° must be reduced to have both generators nearly equal.
- Final adjustment has to be done once again with around 75 % load on each generator if required.
- With proper adjustment there should be no/little movement from governor e-motor.
- This procedure should be done with all generators.
- It is very important to remember that governor droop should not be adjusted as this is done on the test bench in workshop after overhaul.
In conclusion, I cannot emphasize enough the importance of following the manufacturer’s manual instructions regarding engine or any other equipment checks and adjustments. Failure to do so can lead to this kind of situation where the equipment fails to work as intended, thus jeopardizing crew and vessel safety especially during vessel maneuverings and channel transiting, where a black out can lead to a serious accident. Junior engineers need to understand that if they encounter challenges on understanding the instructions, they should reach to their senior engineer officers for guidance. If a senior engineer refuses to do so, it means that he doesn’t deserve his rank and position onboard.
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