Generator Hunting Issue

[Alan Wilson]

Good Day,

I have a issue with a 130kVa generator of ours, to give you an overview of the history and what repairs i have carried out already. The alternator had burnt out (Generator) so we replaced this (Meccalte). We also replaced the speed control unit on the generator (Model ESD51111) as the previous one had not failed on this unit but was removed to be placed on another gen-set.

So prior to replacing the alternator we had the same issue with the gen-set, where it has extreme hunting issues. On start up the unit immediately goes into a violent hunt. We are unable to stabilize the gen-set on the speed control unit, we have since replaced a sensor on the fly wheel as it was advised that it was damaged and this could be sending the wrong information to the governor (Electrical Governor). So this was done but has had no change on the behavior of the engine, we have removed the fuel rack and injectors that have all been tested and are in correct working condition. I have noticed that if i hold the governor in place manually then the engine runs normally and can maintain RPM. I have had the governor tested however and the come back was that its fine. I am sure there is an electrical problem either with the Governor or the signals being sent to the governor on fuel control however I am now stuck on where to go next.

If it is important to note : (Although not the correct practices) i drilled a hole through the back plate on the governor housing and placed a bolt through it to restrict the back travel available on the governor rack, this in turn did help to stabilize the engine however after running for about 10 minutes the RPM ran away, all emergency stops failed to shut the engine down including the manual emergency switch. I then had to pull the fuel line to the distribution block and wait for it to run dry. Any assistance from here would be greatly appreciated.

The generator is a Chicago Pneumatic Build (Atlas Copco), Engine is a cummins BT6 with the Chinese fuel block. Spec'd at 1500RPM 50Hz

 

[waross]

I had a similar problem. Look for binding in the actuator that moves the fuel rack. I had one that was sticking. It was power to actuate and a spring return. It developed internal friction and the spring do not have enough strength to return the rack.
I note that the governor has been replaced.
Check for binding on the engine side of the rack.
You may need some lubrication, something may be bent or a spring may be broken.
Failing that:
Look at the wiring between the sensor and the governor.
Possibly replace the wiring.
Check the installation of the sensor. RTFI!
Be sure that you are using the correct adjustment procedure when you install and check the sensor.
Check the power supply wiring from the battery to the governor.
Try running a temporary wire directly from the battery to the governor for testing.
Check the rear main bearing for excess clearance. (Try prying up on the generator drive plate.)
Do you loose oil out the rear main seal?
Review you setup procedure and settings for the governor. You may be mistakenly using the wrong setting each time you setup the governor.
Check the model number of the governor with the manufacturer.
I had a problem with an uncontrollable generator.
The governor had been changed.
I called the governor manufacturer.
I was told that that governor was not capable of controlling that engine at that speed.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Alan Wilson]

Hi Jimmy,

Thank you for the reply. We have not changed the governor on the genset, although we do believe the fault is here. The part is a Bosch build BYC and we have Bosch involved in the fault finding now as well as cummins, all three of us are still unable to locate the issue. One the replacement of the Alternator where was no oil leak present and i would imagine is there was a seal issue we would have seen this on the replacement of the alternator. The Connection plate on the engine side to the fuel rack seems loose to touch so I am not sure if there is any binding present there.

I have not worked with many of these fuel systems so i am not sure what is normal, saying this there is quite alot of play on the governor solenoid side, which could be throwing the fueling off. We will test the unit as suggested against the battery today to ensure it is not sticking there. I am new to this site, so would it be possible to send a video of the unit in action?

Side note: is it possible that the wrong speed control unit has been installed here?

 

[waross]

Side note: is it possible that the wrong speed control unit has been installed here?

Yes, I have seen that.
Normal governor action:
1: There is a slight increase in load and the set slows slightly.
2: The governor detects the slight drop in speed and opens the fuel rack to bring the frequency back up.
3: As the speed approaches the proper frequency the governor eases the fuel rack back to reduce the flow of fuel.
4: The set stabilizes at the new frequency.
The governor uses power to open the rack and can overcome slight friction.
The governor may use a spring return. The return spring may not have enough force to overcome some binding in the linkage.
This will lead to the engine over speeding until vibration shakes the mechanism loose and the fuel flow is reduced. The cycle tends to repeat.

Note: The action is proportional. The normal droop setting on that size set is 3%.
At no load the set will be running 3% fast, eg: 61.8 Hz for a 60 Hz set.
At full load the set will be running at 60 Hz.
Example: The set is 50% loaded. The frequency will be 60 Hz x (1+(3% x 50%)) = 60.9 Hz.
The load increases by 10%. the stable frequency will drop by 3% x 10% or 60 x 3% x10% = .18 Hz.
The new stable frequency will be; 60Hz x (1 + (3% x 50% x (1-10%)) = 60.81 Hz.

Bill
--------------------
"Why not the best?"
Jimmy Carter