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Old 24-02-2020, 14:05   #91
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Re: spit balling, AC gen on front of main engine..

There are two aspects which must be considered in evaluating whether or not the arrangement of a crankshaft end will sustain a level of power transmission; the torsional capability, and, whether it will resist the shock loadings likely to be imposed in service.

Since there is never the rapid impositions of loadings experienced by say a mechanical drive being suddenly engaged with a high reving engine, a genset might be successfully driven from the front of an engine without damaging it.

From a pure engineering judgement basis ie. without any calculations, I'd propose that up to about a 5-6 kW genset could be directly driven from the front end of a 3GM30 without it causing problems.
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Old 24-02-2020, 17:58   #92
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Re: spit balling, AC gen on front of main engine..

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Originally Posted by CassidyNZ View Post
Thank you, I learned something today.

But at the same time I’m left a little puzzled. So the governor reaches equilibrium at any speed set by the “throttle” lever. When the load decreases, it reduces fuel, when the load increases it provides more fuel. OK, I get that.

So why, when I switch in one of my alternators and increase demand for horsepower, does the RPM drop a few hundred and stay there? Why does the governor not compensate and lift the RPM back to the original setting? After all, the alternator is only drawing 4hp, hardly overloading the engine.

Another thing that bothered me with the article I read is that it said in the event of a loss of oil pressure the governor will shut the engine down, acting as a safety device. But if the pressure drops, surely the same drop will be experienced on both sides of the governor and equilibrium and consequently, engine speed will be maintained. I know the practicality of this to be true because I once had a total loss of oil pressure and had to dive for the throttle lever while the low pressure alarm screamed in my ears. So I guess the governor that acts as a safety device has more clever stuff than a normal one.

Anyway, clearly I don’t have the expertise to meaningfully engage in this discussion so I’ll bow out.
The mechanical governors fitted to most general use diesels rely on the centrifugal force generated by spinning weights against a spring to control the rack setting in the fuel injector pump. Another spring which is tension adjusted by the position of the throttle lever on the pump adjusts the variable speed setting. The droop you see with slightly varying loads is caused by the stickiness of the mechanical system.

Diesel driven generators required to have precise speed and consequent AC frequency control tend to use electrically controlled, servo mechanisms. The electrical speed signal controls a small valve which uses the engine oil pressure to move a piston which controls the rack setting.

The spinning weight mechanism enjoys a long history in speed control and is the device with two balls and cranking calipers seen on old steam engines.
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Old 24-02-2020, 19:47   #93
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Re: spit balling, AC gen on front of main engine..

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Originally Posted by RaymondR View Post
There are two aspects which must be considered in evaluating whether or not the arrangement of a crankshaft end will sustain a level of power transmission; the torsional capability, and, whether it will resist the shock loadings likely to be imposed in service.

Since there is never the rapid impositions of loadings experienced by say a mechanical drive being suddenly engaged with a high reving engine, a genset might be successfully driven from the front of an engine without damaging it.

From a pure engineering judgement basis ie. without any calculations, I'd propose that up to about a 5-6 kW genset could be directly driven from the front end of a 3GM30 without it causing problems.
We know the manufacturer's recommendations for front pulley torsional loads is often exceeded by many aftermarket alternator installations. Does anybody know of this can be actually attributed to real problems?
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Old 24-02-2020, 19:58   #94
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Re: spit balling, AC gen on front of main engine..

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Originally Posted by Q Xopa View Post
We know the manufacturer's recommendations for front pulley torsional loads is often exceeded by many aftermarket alternator installations. Does anybody know of this can be actually attributed to real problems?
Do you mean torsional loads or lateral loads. The lateral loading on a crankshaft for the same torque and belt tension depends upon the pulley diameter.
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Old 25-02-2020, 02:22   #95
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Re: spit balling, AC gen on front of main engine..

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Originally Posted by CassidyNZ View Post
Anyway, clearly I don’t have the expertise to meaningfully engage in this discussion so I’ll bow out.

Asking a good question, or saying something wrong which stimulates good discussion, is just as valuable as anything else anyone does in this forum. I've learned more from the wrong stuff I've said than from anything else I do, and others learn from it too. So no need to "bow out"!


Quote:
Originally Posted by CassidyNZ View Post
But at the same time I’m left a little puzzled. So the governor reaches equilibrium at any speed set by the “throttle” lever. When the load decreases, it reduces fuel, when the load increases it provides more fuel. OK, I get that.

So why, when I switch in one of my alternators and increase demand for horsepower, does the RPM drop a few hundred and stay there? Why does the governor not compensate and lift the RPM back to the original setting? After all, the alternator is only drawing 4hp, hardly overloading the engine.

It's a good question. I think the answer is that it should not do that. On my engine, you can hear the engine tone change when my 2.6kW alternator kicks in, as more fuel is injected, but the RPM does not change. There will be some hysterisis in the governor control feedback, but I do not believe that this should allow a variation of a "few hundred RPM".

EDIT: I see that RaymondR has posted a really convincing answer to this question.

Quote:
Originally Posted by CassidyNZ View Post
. . . Another thing that bothered me with the article I read is that it said in the event of a loss of oil pressure the governor will shut the engine down, acting as a safety device. But if the pressure drops, surely the same drop will be experienced on both sides of the governor and equilibrium and consequently, engine speed will be maintained. I know the practicality of this to be true because I once had a total loss of oil pressure and had to dive for the throttle lever while the low pressure alarm screamed in my ears. So I guess the governor that acts as a safety device has more clever stuff than a normal one.. . .


I don't think all diesel engine governors work like that. As far as I know, the one on my Yanmar does not. In any case, there is nothing inherent to the design of them, which would require them to work that way.
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Old 25-02-2020, 03:24   #96
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Re: spit balling, AC gen on front of main engine..

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Originally Posted by RaymondR View Post
Do you mean torsional loads or lateral loads. The lateral loading on a crankshaft for the same torque and belt tension depends upon the pulley diameter.
My understanding listed HP limits must be referring to Torsional loads. I don't see any mention of belt tensions listed by Yanmar in relation to the front pulley loads.

I'm sure I could be wrong.
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Old 25-02-2020, 23:07   #97
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Re: spit balling, AC gen on front of main engine..

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Originally Posted by CassidyNZ View Post
Thank you, I learned something today.



But at the same time I’m left a little puzzled. So the governor reaches equilibrium at any speed set by the “throttle” lever. When the load decreases, it reduces fuel, when the load increases it provides more fuel. OK, I get that.



So why, when I switch in one of my alternators and increase demand for horsepower, does the RPM drop a few hundred and stay there? Why does the governor not compensate and lift the RPM back to the original setting? After all, the alternator is only drawing 4hp, hardly overloading the engine.



Another thing that bothered me with the article I read is that it said in the event of a loss of oil pressure the governor will shut the engine down, acting as a safety device. But if the pressure drops, surely the same drop will be experienced on both sides of the governor and equilibrium and consequently, engine speed will be maintained. I know the practicality of this to be true because I once had a total loss of oil pressure and had to dive for the throttle lever while the low pressure alarm screamed in my ears. So I guess the governor that acts as a safety device has more clever stuff than a normal one.



Anyway, clearly I don’t have the expertise to meaningfully engage in this discussion so I’ll bow out.


To re state what has been wisely pointed out by several previous posts, there are basically two distinct types of governor, “constant speed” for applications that require a steady power input regardless of the load such as generators that need to stay on frequency but also situations where the load might frequently be suddenly removed. The second type of governor is “variable speed” and permits the engine to be held at a given speed for a given load. With this type , if the load is removed without changing the control lever position the engine will increase in Rpm, often by a lot if the load was great. The governors achieve this through several different techniques, mostly by mechanical flyweights that activate a control linkage or a mechanism that adjusts the fuel rack position. Electronic governors are often fitted to engines with variable speed governors so that they can be used as generator engines.
The Governor that you mentioned as having a low oil pressure shutdown is probably the “King of em all” the Woodward hydraulic series well known in the high end of the power generation industry.
AMSA does not allow auto shutdown of propulsion engines and even big generators are restricted as well BUT if a generator has a Woodward Governor that loses its internal hydraulic oil, the failsafe is a shutdown rather than the less than welcome ungoverned overspeed. Here’s a pic of current Woodward governors during overhaul.
Incidentally the term “governor droop” is the measured increase In rpm when all load is suddenly removed and it is a necessary fluctuation when synchronizing a pair of alternators in parallelClick image for larger version

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Old 26-02-2020, 15:04   #98
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Re: spit balling, AC gen on front of main engine..

The dreaded digitization is creeping into the precision governor field. I was visiting a friend at his place of work when his assistant came in and informed him that their $600,000/day operation had been interrupted for four hours whilst a cascading fault had shut down the four main paralleled AC gensets was remedied.
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