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India - Member - New Member

Join Date: Nov 2009
Location: delhi , india
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causes of hunting in diesel genrator?

11/28/2009 3:21 PM

i want to know what are the causes of hunting in diesel gen.?

gen rating are as follows

2500kva,2405 amp. 720 rpm, 0.7pf, 60 hz,10 pole.

also tell me what r the remedies of hunting.

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Guru

Join Date: Oct 2009
Posts: 2061
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#1

Re: causes of hunting in diesel genrator?

11/29/2009 3:24 AM

There can be many resaons for hunting as:

i) Improper Regulation

ii) Poor Excitation

iii) Unstable loading

iv) Harmonics

etc.

Each issue has to be addressed seperately.

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Power-User

Join Date: Oct 2009
Location: Istanbul. European side
Posts: 151
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#2

Re: causes of hunting in diesel genrator?

11/29/2009 4:09 AM

Hello

The most common reasons for hunting (We call it searching) is the Gain abnormality at the speed governor.

It appears you have an electronic governor.

Speed of the engine is detected by means of the magnetic pickup, of reading the number of teeth passing through on the flywheel of the engine. (I'ts a teethed ring around te flywheel)

This magnetic pick up counts the number of the teeth in any moment and transfers this data to the electronic governor.

Governor evaluates this data and arranges the speed of the engine accordingly to achieve a constant speed of 1500 or 3000 RPM. (Possibly yours is 1500 RPM or 1800 RPM in the 60 Hz case) At any moment and at any load.

Now the level of the gain is important when evaluating the data from magnetic pickup to the governor.

The speed of the engine and the load applied on the engine is floating. When load increases, speed goes down, when load decreases, speed goes up.

High gain level means quick response of the engine against the load variation. (Speed also varies accordingly). Quick response is not always gives good results. High gain level means high feedback and this brings oscillations.

The governor on the engine continously tries to find the correct speed and infinitively adjusts the speed. But the feedback data from the magnetic pickup is exagerated by the high gain value, therefore readjusts and readjusts again, and it goes on like a closed loop.

Try to lower the gain setting, or play with the droop setting if existing. But not change the speed setting on the governor. Otherwise your constant speed as well as the frequency changes.

Kindest regards

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Guru
Engineering Fields - Marine Engineering - New Member

Join Date: Aug 2007
Location: Australia
Posts: 1630
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#3
In reply to #2

Re: causes of hunting in diesel genrator?

11/29/2009 8:48 AM

You need to be careful when toying with droop settings on diesel gen sets because this can cause problems with voltage and hertz settings...........particularly if you exceed approx. 1,25% droop........the r.p.m. changes become too great, causing problems with sensitive electronic equipment.

Apart from the governing of the engine.........electronic or otherwise........mechanical problems may, in some cases, also cause hunting.

One should not stuff around with equipment they know nothing about, (particularly governors on diesel engines.......it could cause catastrophic failure) and from the question, I do not think that Sandeep has that knowledge, otherwise the question would not have been asked.............no disrespect to Sandeep.

Most decent electronic governors for diesel gen sets do have an extremely small deadband and have a quick response, without hunting.........i.e. they can be set for isochronous governing.........or with droop for a main engine application........where you may have up to 9% droop.

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Power-User

Join Date: Oct 2009
Location: Istanbul. European side
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#4
In reply to #3

Re: causes of hunting in diesel genrator?

11/29/2009 9:55 AM

Out of mechanical reasons ( I am not experienced enough to give an advise for the mechanics),

Decreasing slowly the gain setting, under observation may help. Very low gain may result loosing the speed control.

Engine speed setting on the governor must stay at factory set. If lost, the engine must be run without load and the speed must adjusted to fix 1500 or 1800 RPM by checking the frequency at the output or by means of an RPM meter.

Coming to Droop setting. Droop is essentially taken into consideration when Droop Paralelling the two generators. This is the simplest parallelling way of the generators.

Generators in parallel are electromechanically locked. They control the phase angle of each other and try to match.

Advanced angle means more load according to the partner generator in parallelling.

To achieve proportional load sharing and avoid one of them overloading, Droop setting plays here the essential role.

When you lower the droop setting, engine goes to be mild to obey the other generator's forcing to increase or decrease the speed. In other words Gives permission to other generator to retard or advance his phase angle by drifting.

Otherwise (if the droop setting is high) the generator engine strictly dependent to it's own magnetic pickup and wild for external angle corrections.

I never faced problems with the droop setting when the generator is standalone and not paralleled with an other one. Droop control is almost effectiveness in standalone situations. No uncontrolled speed increase or decrease. It can be left at "0" null position. Therefore it is not playing any role on the speed of the engine. However if genset is loosing the speed in maximum loads, droop can be increased a little bit.

Regards

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Guru
Engineering Fields - Marine Engineering - New Member

Join Date: Aug 2007
Location: Australia
Posts: 1630
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#6
In reply to #4

Re: causes of hunting in diesel genrator?

12/01/2009 9:33 AM

I never faced problems with the droop setting when the generator is standalone

You haven't lived..........in the good old days most hydro/mechanical governors had a set droop in them, and you could not achieve isochronous governing even though you could adjust the droop.

An exception to this was a few of the Woodward governers........and I used to take students over to one of the patrol boats (they had 2 x 3/71 Detroit gen sets), and showed them what happened when a governor was set on zero droop.........it used to hunt wildly..............this was why droop requirements were needed for gen sets (1-1,25%) and main propulsion engines (8-9,5%)

I do admit of course that electronically controlled has changed this.........I am not a proponent of it in marine main propulsion units.........I would not like the possibility of my main engine shutting down because of the failure of a $2 electronic component, when one is in restricted waters.

I have always used synchroscopes for paralleling alternators..........although this is done automatically nowadays, one should always know how to parallel manually.............these aromatic systems are notorious for failing.

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Anonymous Poster
#5

Re: causes of hunting in diesel genrator?

11/29/2009 2:23 PM

despite havin all kinds of problems mentioned above regaRDING hunting in diesel or gas gensets,,,, the actuator may also need to be checked ...specially its rod,,, if its motors bearings have gone loose in its housing tha the rod doesnt sticks to its poisition when at idol and may move a bit with the vibration......rest do consider all of the above mentioned.

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Guru
Engineering Fields - Mechanical Engineering - New Member

Join Date: May 2008
Location: CHENNAI, TAMIL NADU, INDIA.
Posts: 1854
Good Answers: 64
#7

Re: causes of hunting in diesel genrator?

09/30/2016 12:48 PM

Dear Mr. sandeep,

The reasons for hunting will be as follows.

1. Governor is Too Sensitive

2. Fuel quantity injected is not uniform inaccordance with the load.

3. Sudden load variation frequently.

4. Fly wheel is not rigid and key might have sheared and speed of fly wheel is less when compared to engine speed.

5. Disturbance in quantity of air entering the cylinder resulting in proper combustion.

6. Carbon soot is excessive.

DHAYANANHAN.S

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