Regulated output generator

[compig]

Did somebody correct the math on this?


> a 600 rpm engine and 60 hz output frequency, there are roughly 10 rotations of the crank in one complete output cycle. That's 2.5 power strokes.

600 rpm = 10 strokes/sec = 5 power strokes/sec = lots of 60Hz cycles between power strokes.

600 rpm = 10 REVS /sec , but on the power stroke once every 2 revs power or force is only exerted on part of that revolution of the crank , for approx 100 degree's or less than a 3rd of the revolution. It's the number of sine wave cycles that occur in that 3rd of a rev thats the issue.

[compig]

Found it , http://listerengine.com/smf/index.php?topic=3895.0   , 10th post down by MJN.

[Tom]

Jens, you are indeed an honorable fellow.

[MacGyver]

I certainly think that a good controller could keep the average RPM much more constant by watching the load current and "anticipating" governor changes before RPM changes occur as Jens mentioned.
And obviously the RPM  variation that's due to the power stroke can only be cured with more flywheel mass and no amount of "controller will help that problem.

But I guess I'm still not sure what all the fuss is about..? Why a bother with a PID controller?
What equipment do you have that can't  tolerate a plus/minus 2 Hz variation from "optimum"?

I've got my unloaded frequency set at 61 Hz, and with a 3KW load it drops to 58.5 Hz..
When going from no load to full load or full load to no load it never goes outside of a 58Hz to 62 Hz range. That's +/-  3.5%

When I cleaned/assembled my 6/1, I did some minor detailing on the governor parts to make sure everything worked smoothly, and especially cleaned, smoothed, and radiused the area where the weights contact the sleeve that they move.
I had to do some work on the external linkage parts to make them work without binding, then I spent time selecting a spring with the right length and stiffness to get good  response.

Certainly the governor response could be better, but it seems pretty darned good now and none of my equipment has any complaints about it.
And any equipment that whines over a =/- 3.5% variation in frequency doesn't inspire much confidence anyway. Even most clocks  use quartz oscillator instead of line frequency to derive the time these days. I suppose your ancient record turntable with the synchronous motor might make your music sound kind of funny, but I can't imagine anything else that would freak out about it.

I'm far more worried about the "short term" variation and resulting flicker that comes from the power stroke. That IS annoying.
I don't see any cure for that except a good AVR and/or more flywheel mass.

[Tom]

The clock on our oven looses time when on 'roid power. I've got the governor set to hold 120v with a 3125 watt load. I don't have a HZ meter to see where that is at, but it must be a bit low. I am running a "modern" rectifier in the ST5 so the voltage may be a bit high.

Interestingly I am seeing a consistent 3 volt difference between the legs. It stays the same from no load to full load. Perhaps there is a missing winding or 2 on the field coils.

[compig]

Occasionaly I put a digital voltmeter and frequency counter on my house supply. Variation has been as much as 8 volts and 1.2 Hz from a nominal 240v and 50Hz supply !!

[MacGyver]

If your average speed is off by 0.2% (about 1/8 Hz) , that's still almost 3 minutes a day discrepancy on a line frequency driven clock.

I guess it's no problem for the PID controller to keep the average speed correct if it has a good timebase to reference from.

[mobile_bob]

i did a similar check on the power company frequency here in south tacoma a while back
it varied from as low as 58.9 to as much as 60.2 hz if i recall, i do remember thinking that odd at the time.

maybe we get our power off the columbia hydro and a beaver got sucked through the pipe?



it just slowly went up and back down over about a minute of so that i was checking it.

i always assumed it would be spot on 60.00000 hz,, maybe it ain't?

bob g

[compig]

Thats gotta be almost impossible with all the loss's and demand fluctuations that must occur. Presumably there are performance regulations to be met though ?

[AdeV73]

Ooh, I know a bit about this stuff (more than I currently know about Listers...!)

Your home/industrial supply has, believe it or not, exactly the same problems as your Lister[oid] supply: Varying loads cause the generators to bog down or overspeed, which changes the frequency and voltage of the supply.

The power companies will be switching generators in & out to keep the voltage & frequency as close to the desired values as possible (230v/50Hz in the UK; whatever the official US voltage is these days (117v rings a bell) and 60Hz across the pond). Entertainingly, the power companies have to do "demand management", or - roughly - gaze into a crystal ball, to anticipate future power requirements and pro-actively switch generators in or out.

For example: Here in the UK, there's an advertisment break half way through Coronation Street. IIRC, about 15 million people watch Corrie, and something like 5m of them will jump up and put the kettle on (to make a cup of tea, naturally!) when the break arrives. That's approximately a 10 million kW [10GW] change in load in the space of a few seconds. However, the power company know this is going to happen, and have their 10GW of generating capacity on "hot standby"; they start switching it in as soon as the ads start; and (literally) watch a big "frequency meter" which they try to keep as close to target as possible. I can't rememeber the range they have to keep the frequency to, but it's around 1-2hz either side of 50, or something of that order.

In the US, I guess the closest analogy would be when you get an ad break at the Superbowl - when everyone leaps up to make a coffee (or do you all just grab a cold beer?).

Anyway... sometimes, the system goes wrong. If the frequency (in the UK at least) drops below a certain level (or goes above, presumably), then the grid starts tripping out. Low freqency is caused by an overload - we saw this recently when a nuke & a coal station both unexpectedly tripped, leaving insufficient generating margin to maintain 50Hz; with the result that approximately 1/4 of the UK lost power for between 5-120 minutes, depending on area. Ironically, that event was what started me down the road of looking at Lister power.

There's quite a bit of stuff about this on Wikipedia, some of which is quite accurate... Another interesting factoid about the grid: If you attach a generator to it, the grid will force the generator to synchronise to it...

e.g. Restarting the Grid in a total blackout situation: http://en.wikipedia.org/wiki/Black_start

[compig]

Oh goody , a power company professional !! Meant in a respectful way !!  Is the official UK mains now 230 V ? Not 240 ?  Can you enlighten me on the issues regarding selling my surplus Lister power to the grid ?

[compig]

Coronation St in the USA !!!!  Arrrgh , thats my illusions shattered then !!

[AdeV73]

Oh goody , a power company professional !! Meant in a respectful way !!  Is the official UK mains now 230 V ? Not 240 ?  Can you enlighten me on the issues regarding selling my surplus Lister power to the grid ?

Ah, sorry, no - not a pro... related to someone who works in what used to be the Electricity Board's R&D labs, so I've picked up a bunch of knowledge via osmosis... I also worked there for a year (some 15 years ago now, eek), but on HV transmission line fault finding (echo location of cable faults - fascinating stuff).

As for voltages, IIRC mainland Europe used to be 220v, the UK 240v. In order to harmonise, Europe have raised their average voltage to 230, just as we've lowered ours... something like that anyway, I'm a bit fuzzy on the actual numbers there. Certainly 230v is the "new" standard, though.

As for selling your surplus power - you're on a hiding to nothing at the moment. Most elec companies simply aren't geared up to do anything like that; and those that have the capability are desperately trying not to push it... In one of life's ironies; Big Power has a real (and genuine) problem with allowing micro-gen plants, such as people with solar arrays, Listers (or any other genset), wind turbines, etc., to sell back to the grid.

The problem is one of safety. At the moment, the power company can isolate any given area by operating the correct sequence of switches. 'Leccy workers can now go and do stuff - like repairing switchgear, transformers, etc. - safe in the knowledge that there's no power on. Now consider the situation where, half way through the repair, someone attached to the switched-off area throws their genset online; BANG! One fried worker.... And one person - assuming they survived - is wondering why his genset leapt a foot in the air....

IMHO, it's not something that's likely to happen in the near future; not unless the elec companies can guarantee that your genset is isolated off the mains if the power is deliberately off.


Jens: 3 breaks to a 1/2 hour! I don't know I could cope with that. It was bad enough watching F1 on ITV when they stuck 5x 3 min breaks into a 90 min race [ITV always claimed to only put 4x 2.5 min breaks in, but they lied consistently]. Can you not watch Corrie over t'Internet? [disclaimer: I have not tried this]. Just in case you can't, I can give you a synopsis of any episode right here:- Some people will shout at some other people; a mysterious stranger will arrive & mysteriously fall into a relationship with someone else who just lost someone who left/died recently. An enormous number of "never heard of before" relatives will come & go. Someone will buy a pint. A fight (or scuffle, at least) will break out at least once, and someone somewhere will cry. Theme music & credits. There - that's saved you an hour & a half per week

Oh, PS: HV=high voltage (11kV & above IIRC), LV=low voltage, typically 440 or 230vac

[compig]

Ah yes , I had overlooked the safety thing. Ah well , I'll keep it all to myself then  !!  Thanks for that info , very interesting.  Whats the actual efficiency of prime power generation plants now ?

[jzeeff]

Just think how much better life would be if we all used Tivo (or any TV time shifting device).