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Power stability with PTO generators
This subject came up in the "Receiver hitch for iMatch" thread and I thought I'd start a new one here.
How do PTO generators maintain voltage and frequency stability when powering variable loads (refrigerators and freezers cycling on/off, etc). It seems to me this would be a concern. I know my standalone Gillete genset throttles up and down to stabilize voltage and frequency as the load changes, but I don't see how a PTO generator can do this. Is it even a problem?
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Power stability with PTO generators
Sounds like the unit you have has an auto idle?
The pto setup once you set it at rpm for freq you need it will be fine unless you hit it with a big draw and it may bring tractor to knees. You'll hear the tractor knuckle into load and work as things start but will be a good sound. RPM may drop a tad but will come right back. Not so with a big draw. Did you ever watch a big tractor run a blower? Same sounds as wads of siliage hit.
One of our friends years ago pulled their 150+hp out with gen hooked up and pulled the big power pole disconnect. Fired off generator tractor bogged way down and would not run the set. When they shut it down to check problem the disconnect lever had worked but it had not pulled the shunts out of the sockets. Good thing no power people on that line then...They got ladder and a stick to force shunts out.
If you have HP enough for your load you will be fine. But you won't run the block  .
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Power stability with PTO generators
Harvey, we have had trouble with people overloading pto generators to the point of melt downs from the heat. The way they do it is to use to big of a tractor to begin with, it never shows the actual load from compensating the tractor engine rpm. Then go in the barn and start turning on the big 5 and 10 horsepower motors. When they see that tose are up and no problem ten start turning on the rest of the lites and overload the generator.
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Power stability with PTO generators
A standalone generator engine has a governor that attempts to maintain rpm under varying loads and so does the tractor engine. As Harvey noted, having a PTO generator that's capable of sustaining a load that the tractor can't carry is a bad idea, although potential problems could be managed by using smaller main breakers if somebody is around to reset the breakers.
Yikes, back-feeding a utility line with a 150hp tractor sure could knock linemen off poles for quite a distance. Fortunate there weren't any nearby indeed. Some immediate probably thought power was coming back on.
I know that utility companies aren't very happy about any kind of transfer switch but they might be even less happy at the idea of somebody hooking into one side of a disconnect. I think transfer switches are set up so it's virtually impossible for the gen feed contacts to be made unless the utility feed is disconnected. Around here we have to use 3-point disconnects and I imagine that most disconnects and combination service panel mains have 2-point disconnects.
Irrespective of code requirements, I like my linemen and know they work in conditions I wouldn't want to work in. I want them be happy so I'll what ever equipment the utility says I have to use even if I'm certain I'm not going to backfeed a line.
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Power stability with PTO generators
Ken, I think you're mixing up auto idle with voltage/frequency adjustment as Harvey pointed out. The speed up, slow down, you notice on your gen-set is just a load triggered automatic throttle, as the load on the engine increases the engine automaically gives itself more throttle. This is purely a reaction to load, nothing to do with maintaining voltage or stabilizing frequency levels.
On most big gen-sets, including our big Winpower PTO gen-set (80 kw. max, 50 kw. continous) on the farm merely have a meter of the "safe range at" type of voltage adjustment, in other words there is a big voltage meter visible from the tractor's seat, you play with the throttle until you get the desired output then just leave it there. The frequency is automatically set internally.
The problem of course with running anything delicate off these things is that even these big monsters can only keep the voltage to within plus or minus 5% of the set voltage point, on 120V. circuit that means the voltage could be anywhere between 114 and 126 volts, computers for example don't like that at all.
Toms comment about the transfer switch is right on the money, when we wanted to re-locate our generator a few years ago, into a shed below the pole on which the meter is installed, the hydro people were VERY involved, they had to approve the design before we could even install it, then they had to inspect it after construction to ensure it was built to spec. The transfer switch in our case also had to be a 3 point break system, the same bars that connect the gen-set disconnect the grid feed, and it is a long throw at that to be sure there is no chance of arcing.
Best of luck.
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Power stability with PTO generators
Ken, I have been asking the same question here and to my self for several months. I think I found the key to understanding the dynamics in one of my tractor manuals.
If I have this wrong I hope someone will speak up and set me straight.
I was pondering the fact that my 4115 as a "low idle" setting (850 rpm) and a "high idle" which is listed at 2650 rpm.
That got me scratching my head until I realized that a diesel engine with no load is considered to be idling even when it is turning max RPM's. The governor adds more fuel when it senses a load, trying to maintain the rpm's as they are set with the throttle.
So a diesel engine with no load turning at PTO rpm burns way less fuel than the same engine, at the same speed, running a big load.
I think when you set the throttle on your pto/diesel/generator there is a minimum amount of fuel that will be injected/burned just turning all the parts.
When you start adding a load the governor compensates by increasing the fuel flow. If you add too big a load, the engine and governor maxes out and the excessive load will begin to drag the RPM's down, and a big overload will overheat the generator and/or stall the engine.
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Power stability with PTO generators
Thanks everyone, I think I understand now. There is no voltage/frequency controller, just a governor to hold the rpms. If the engine doesn't have enough power to handle the load the rpm will drop off, a sign that the engine is overloaded. A little variation in engine speed is normal as loads start and stop until the governor can make adjustments. I can see how electronics may not like the variations in voltage and frequency.
Our genset doesn't have auto-idle, but when it's running I can listen to the engine and tell when loads cycle on and off. I thought there was some sort of electronic controller making those adjustments but I can see how a simple governor could do that job. It's now less murky.
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Power stability with PTO generators
I din't think anyone still made a generator WITHOUT auto-idle.
It is a five cent cost to the manufacturer but makes a HUGE difference in fuel consumption. I have several small portables, various makes of engines, Tecumseh, Honda, Briggs & Stratton, even an old one with a Wisconsin Robin, even it has auto-idle on it. The generators make 110v. even at idle, but as load increases it speeds up to produce larger current capacity.
The easiest way to check is to start a generator with nothing connected, then add a reasonable load, say a circular saw, then shut off the load. If the generator goes from idle to full throttle and back to idle, it has auto-idle. If it goes to full throttle with no load, it is not so equipped.
Best of luck.
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Power stability with PTO generators
My standby genset is approaching five years old now. I'm not sure when auto-idle became a popular feature, but I don't recall hearing about it when I was shopping.
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Power stability with PTO generators
You probably didn't hear about it because by then it was built in to every generator made, regardless of make, calling it a 'feature' would be kind of like saying "and it comes with spark plugs too!".
Best of luck.
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