Multiple AC Source Synchronisation.

[NEO]

Hi ALL,

    I want to synch up several different intermittent AC sources. (and I hope this is the right place in the forum for such a discussion) I will try and be brief about what I am thinking, and hopefully people will ask pertinent questions or better yet point out glaring omissions or errors in my thoughts!

I have a large house and family and even with education and conservation lectures by me and the use of low energy products like CFL's etc, the desire, no the demand to keep all life's electrical luxuries is high.

I/we want all the benefits of being on the grid without being on the grid. and remain carbon neutral.

I want to cut lose from the grid and this is the plan.

1. 5Kw PV array
   
2. I would like two wind mills (home brew) got plenty of wind for most of the year :-) (separate project)
   
3. Solar thermal panels
   
4. 3 small bio diesel gen sets rigged as co generation to supplement power on demand and to add to the thermal solar panels contribution.
   
5. The obligatory battery bank.
   
   

The idea is to have a system that is entirely demand driven and dynamic with no single point of failure.

I am leaning towards outback inverters VFX3048E...anyone have any experience?

I know how to parallel up generators manually but could certainly use some electronics pointers or help to figure out a home brew way of doing the synching up with out actually having to be there to watch the light bulbs or pay for a commercial synchroniser.

I am thinking two mills with different cut in voltages and power curves that overlap so that one is always making power even if it is a little.  Hopefully something somewhere in the system is generating some power regardless of the weather or other environmental conditions.

I am thinking the best way to do this is to trick the inverters I put on the mill/s and the solar panels to thinking they are grid tied by perhaps having a stable "reference" voltage and frequency perhaps supplied from the battery bank.

I am concerned that the renewable connected inverters would disconnect from the bus bar when a load is added like a motor starting or some other induced load that affects the "reference" voltage or frequency.

If the battery bank can absorb any switch on loads for the duration it takes to start and have a gen set settle in order to meet the new demand load. Obviously time is a factor, there is no point in starting up a gen if the "over load/demand" is very brief.

    If demand continues to grow then another source is started up and added. The reverse would also be true if the renewable generators were able to cover more of the demand, then a gen could be dropped out into a cool cycle and then stopped.

Ideally I want the gens to take it in turns so the hour's usage is the same.

Thoughts?

Kind Regards ALL

[fungus]

Welcome to the board,

The general idea that most people go with is to have all the renewable sources directly charging one main battery bank and then the battery bank powering one main inverter, thus making there no need for more than one inverter. If however the inverter(s) available are not high enough capacity then I believe(aand please correct me if I'm wrong) that you could parallel a sinewave inverter and a grid tie inverter together to have more power capability.

[Volvo farmer]

Those Outback inverters work very well with a generator (singular) in off grid situations. I'm having a little trouble understanding what you are trying to do but I think it would be very hard, if not impossible to have three separate generators running at the same time and synch their waveforms.

The traditional way to do this is to run all AC loads through the inverter and off the batteries. If the batteries get too low, the inverter can be programmed to turn on the generator and charge the batteries. I believe Outback inverters can only charge batteries at about 20A AC, if you have more generating capacity than that, the inverter can bypass the extra for your house loads. My experience has been that the transition is seamless, If I turn on or off the generator, all loads, even things like electronics don't even hiccup when the source switches.

I don't know how luxurious you are with your electric loads but my wife runs her hairdryer and a toaster every morning, before it's light, off the batteries. We only have 680W of solar and no wind (yet). On a sunny day like today, I'm still out of absorb and into float by noon or 1PM.

There's tried and true methods for building an off-grid electric system, a lot of this stuff was learned through trial and error, from folks using the technology, over the last twenty years. Maybe it would be best to start with the regular formula that most folks use and play with it later if you don't like how it performs.

[Countryboy]

If you want to be off grid, I would recommend hooking up all of your electric producers to charge a battery bank, and then get an inverter to run off the batteries to power the house.  You need DC current to charge a battery bank.  Solar PV panels produce DC.  If you have an AC producing windmill, you will need to convert that AC production into DC current.  You do this with rectifiers.

If you want all the benefits of being on the grid, while living like you are not on the grid and being carbon neutral, I would recommend that you grid tie.  In a grid tie application, you use the grid like your battery bank.  Any time you are producing more electric than you are using, that excess is pumped out onto the grid.  This will turn older electric meters backwards.  If you need more electric than you are generating, (cloudy windless days) you use grid power.  (and when you start producing again, you replace the power you used from the grid)

Battery banks are limited by how much current you can charge them with.  If you get excellent winds, you will need a dump load to burn off your excess production.  That is wasted electricity because you don't have the storage capacity to save it for later.  In a grid tied application, if you get high winds, you get credit for all the power you produce.

If your monthly production exceeds your grid use, you may even be able to get the electric company to pay you for your electric.  Any electric you put out on the grid is that much less the electric company has to produce.

Being off grid with a battery bank, your own home is 'green'.  Being grid tied, you are 'green' too, and your excess 'green' electric is used by your neighbor, so you help your neighbor be 'green' too.

[NEO]

parraleling generators is not the black art people think it is, the generators should be of the same voltage and frequency preferably identical alternators the process is this; and it works the same for 3 phase. once two are running in sync the process to add another is the same. here is a clip i cut from the web a while ago and it has served me well.

If the neutrals are connected together and then the voltage between the hot

legs of the two generators is measured (hot leg to hot leg and not

hot to ground), the following conditions will be noted:

In phase:  zero volts

180 degrees out of phase: the sum of the two voltages.    Since the

voltages must be the same, this will be 2X the nameplate voltage.

The generators can only be connected together when the voltage

between the hots is zero, e.g. in phase.  This suggests a phasing

method.

The standard power plant method of synchronizing two generators is

to use a very expensive instrument called a synchroscope.  This

instrument indicates whether the incoming generator is faster,

slower or in phase with the bus.  Since the rotors of power plant

generators weighs many tons, the phases must be extremely accurately

matched or else the rotor will be forcibly yanked into phase,

possibly wrecking the generator.  For small units, we don't need to

be so precise.  We can use a pair of lamps.

What you'll need is a couple of lamps hooked in series and connected

between the hot lead of the running generator and the hot lead of

the newly cranked generator.  You'll also need a switch of some

sorts to parallel the units.

If the generators are 180 deg out of phase, the voltage across the

lamps will be 2X the nameplate voltage (240 volts in the case of two

120 volt generators.) and the lamps will burn full brilliance.  If

the generators are nearly in phase, the lamps will be out because

there will be no voltage on them.  If one generator is faster than

the other, the lamps will flicker on and off as the gens are in

phase one moment and out the next.

The procedure is as follows.  Start the second generator.  The

lights will be flickering or slowly coming on and off.  Manipulate

the throttle of the incoming generator which ever direction is

necessary to slow the flickering.  As the speeds become almost

equal, the lamps will stay off for a long period of time and then

slowly start lighting, slowly get fully bright and then slowly dim

again.  You want to manipulate the throttle until the lamps are off

for as long as possible.  You want to close the breaker when the

voltage between the generator is the least.  Since the lamps will go

out before the voltage reaches zero, you'll want to mentally time

the period between going out and coming back on again and close the

switch about in the middle.

Once the breaker is closed, the generators are locked together.

Indeed, you could close the throttle of one engine and the coupled

generator will motor the engine at precisely the sync speed (3600

RPM for small gens).  If the generators are just a little bit out of

phase, then they will be yanked into phase as momentary heavy

current flows between them.  And if you close it out of phase, then

you have a double voltage short circuit.  Usually there is severe

mechanical and electrical damage.

Once the generators are in parallel, the load accepted by each

generator is governed by the governor setting.  The generator with

the most throttle will accept the most load.  On larger generators,

the field excitation is manipulated to control VARs but you don't

have that control and so you have to accept what you get.

Actually, the idea of using more than one generator is very good if

you only occasionally have a heavy load to drive.  If you bought a

generator large enough to run this occasional load, then most of the

time it would be running very lightly loaded and thus very

inefficiently.  Cranking the second generator for only those

occasions when the large load is needed is a good solution.

[Nando]

The idea of doing multiple synchronization steps of multiple AC generating sources becomes quite complex with the protection circuitry that needs to be going into a matrix controlling the different units at the same time.

For Your case, without the need of an expert there 24 / 7, would be to have a master battery bank charged by the different sources and a single AC source to fill your needs.

Incrementing power, as You would like to have, becomes, for the alternative Energy user a kind of nightmare to control -- also, difficult to get the necessary equipment to operate the power sources.

We did one that had a battery bank of 200 volts that was converted to 200+ and 200- supplies and from there an AC converter producing the wanted AC voltage.

The AC modules (large boards, I still have 4 or 5 of them) were rejects of a commercial product each capable of 5 KW with 4 units in parallel that came on automatically with the increasing current.

A power module was added automatically when the current increased to certain level.

Each board had a 5 KW back up module in the board, still after about 15 years the systems is working well, built at a very low cost, indeed

Every power source charged the 200 volts bank, as each power source was available or needed.

The system has a power transformer to isolate the electronics from the external world.

When running machinery, the alternate power sources were used to produce ( really, added to) the +/- 200 volts supplies to improve the efficiency of the system.

I understand that now are changing the battery bank by adding a 200 - volts bank to for additional capacity and improvement -- that was initially taken care for future implementation --

Nando

[NEO]

Hi thanks for the comments.

That's pretty much the essence of what I want to achieve. What I am suggesting is not new nor untried or tested the generator companies have been doing it since generating electricity was marketable, the sources of power or fuel are maybe different.

I do very much want to be off the grid..grid tie is not an option nor is sale of excess at the moment. A demand driven system for me is very efficient and cost effective. As posted above I am looking for ways to get the "kinks" out with the synchronisation...particularly with automating the gen synchronising.

I had considered what you say about all generators feeding the battery bank and then stacking inverters the "outback" way. But I see no advantage in running the gens which make AC and converting it to DC to charge the battery bank only to invert it to back to AC again....very, very wasteful IMO, especially as I know I can cascade as many gens as I like (alternators permitting) the out back inverters have contacts to auto start and gen controls. What is missing is a bit of electronic wizardry to interface with that and the gen/s.

          I think also the battery bank can be much smaller because it only needs to hold the troughs and brown outs...less maintenance there, less expense. Perhaps a bank that could carry the property for say 12 to 24 hours only. Unless I am missing something else??

Thanks for the thoughts keep em coming

Regards

[Countryboy]

A demand driven system for me is very efficient and cost effective.

Think about what you are proposing.  It is ridiculous.  A demand driven system will force the windmills to produce more power as you need it.  How do you propose persuading the wind to blow harder, exactly in the amount needed?  How do you persuade the sun to shine a little bit brighter to get the PV panels to produce more, as demand increases?

With fancy electronics and a gearbox, you can get a windmill to produce constant 60 Hertz AC, and with variable pitch on a large enough turbine, you can get it to produce the level of power you want.  However, it certainly won't be cost effective.

I had considered what you say about all generators feeding the battery bank and then stacking inverters the "outback" way. But I see no advantage in running the gens which make AC and converting it to DC to charge the battery bank only to invert it to back to AC again....very, very wasteful IMO,

You're overlooking one teeny tiny super critical thing.  Windmills produce what is known as 'wild AC'.  While it is AC current, the voltage, amperage, and frequency all vary.  It does not remain constant.  The electric appliances in your home require pure AC.  They need a constant voltage, at a constant frequency.

If you can find a way to convert variable frequency AC into a constant frequency AC current easier than rectifying the AC to DC and then inverting back to AC, we want to know.

There is a huge hydroelectric dam between Venezuela and Paraguay, if I remember correctly.  The grid in one country uses 50 Hertz AC, and the other uses 60 Hertz.  There are about 18 or 20 generators in the dam, with each country owning the half on their side.  One of the countries (I forget which) sells a lot of their electric to the other country.  However, the electric they produce is a different Hertz than the buyer's need.  How do they convert the 50 Hz to 60 Hz?  You guessed it - they rectify several megawatts to DC, and then run it through an inverter to produce the desired AC frequency.

Unless I am missing something else??

You're missing a lot of somethings here.  It is easy to say you want your generators to all produce the exact same frequency and voltage.  It's a totally different thing to be able to actually get them to do it.  Synchronizing multiple generators, which produce from fluctuating power inputs, is far more difficult than it sounds.

I think also the battery bank can be much smaller because it only needs to hold the troughs and brown outs...less maintenance there, less expense. Perhaps a bank that could carry the property for say 12 to 24 hours only.

Most people choose a battery bank that can sustain them for 3 days.  Sometimes it is cloudy for a couple days straight, and the wind doesn't blow much.  Also, please keep in mind that you do not want to run your bank below 30% charge if you want the battery bank to last very long.  Plan on a super expensive, extremely large battery bank if you want to be able to maintain a grid lifestyle off grid.

You haven't even addressed the issue of charge controllers, to prevent overcharging your battery bank, which is just as destructive as an undercharged battery bank.

I have a better idea for you.  Eliminate the battery bank.  Simply use electricity only while you are producing it.  You have lights while the sun is shining on your PV panels, and when the wind is blowing.

Personally, I get the idea you think these generators will be able to constantly produce nearly the amount you constantly consume, with minimal periods of slightly lower production and minimal periods of higher production.  If you want a constant source of electric, you need to look at hydro - not wind or solar, which is variable.

[NEO]

Thanks for that Nando, very much appreciated

                   Certainly something to consider. You will I trust forgive my stubbornness if I try to persevere a little more:-)

It's very easy to come buy G77 disconnects purposely designed to disconnect power systems from each other and to reconnect them speficaly for grid tie applications where the inverter does not have the necessary disconect built in to sense the loss or change of grid supplied power. The relays could be either in ROCOF or vector Shift relays or even combined units that perform both functions.

       I was hoping someone would know if I can use them in some configuration for what I want to do.

       For those that don't know ROCOF (Rate of Change of Frequency) relays operate by monitoring the rate of change of frequency with respect to time (*f/*t). The relay will operate if *F/*t exceeds a preset limit in Hz and this is adjustable.

       Vector shift relays monitor the length of each cycle, operation of the relay occurs if there is a step change in the length of a cycle or cycles. The step change is measured in degrees and is also configurable. Obviously a combined unit does both functions.

       Into the mix for additional parameters and the safety conscious we could add Under/Over voltage sensing relays and under/over frequency sensing relays. Also the presets are adjustable.

These are all readily available, affordable units designed with very high tolerances and failsafe performance. I was thinking of a modular approach.

        It was my thought that by measuring the RPM of the gens I could automate the gen speed synchronisation with a small servo. Then use the relays to close a contactor when the gens were in phase.... or alternatively or in combination monitor the bulb link between the HOT sides with a timer that measured how long the voltage was at zero in conjunction with another timer to govern the zero voltage duration and at the zero voltage point close a contactor. With droop governors on the engines allowing both units to evenly load share with out putting undue stress on either unit.

    Start up and close down could be controlled by monitoring the flowing current with a ct coil or coils and another timer contactor configuration. Drop out of sources governed the same way.

Regards

[NEO]

If you will permit, addressing in sequence your response.

With respect I never once suggested that I could alter the wind or the sun! please read more carefully.

I fully understand the principle of wild AC. At no point did I mention trying to sync wild AC

Please read more carefully

Taking the above into account I have missed nothing...yet

The outback inverters I proposed connecting to a battery bank and the wind mill and the solar array ALREADY synchronise with an external stable voltage and frequency. No miss alignment there!

I am pleased you mentioned charge controllers I was thinking of a couple of MPPT tracking MX60 again from outback connected to the array and brand X for the rectified DC from the mill...would you like to make a suggestion or flame away....

The post was about synching up AC sources particularly my bio diesel generators...I have shown how it can be done and stated another methods one a commercial approach the other a manual approach.

Hydro is not an option no water I am afraid.

I can already synch my multiple AC generators using the above described method...EXACTLY synchronised for voltage and frequency no deviation at all and load sharing.

I think that you completly missed the point that I have 3 small generators.

I am just looking for someone with a little knowledge of AC control devices to suggest ways of achieving the auto AC synchronisation....the battery bank/inverters from the renewables synchronise! The generators can be synchronised I want to automate the joining of the two systems...this is not rocket science and there is no requirement for deity status to alter the elements!

The very fact the renewable vary with output is the sole reason I want to supplement the demand with my gens!!

To clarify then;

A solar array and wind mill or mills feeding a battery bank (no size stated) with stacked sine wave inverters for the output..(They can stack to make 30 or 36KW (not that I want that much!)) . These inverters already auto synch! They are designed for grid tie.

My generators auto starting and auto synchronising home brew style and auto stopping based on any excess demand placed by my home and business.

It's often considered polite to ask a question than make an assumption when you don't understand a premise...

Hope this helps to clear up the missunderstandings you had if not I can try again.

Kind Regards

[NEO]

I was under the impression that in the damn example it would have been better to direct drive an alternator of the phase voltage and frequency required by a motor of the voltage and frequency and phase available providing that you dont want more out than you can put in.....I would have expected poly stacked rectifiers in the multi megawatt range to be less efficent loosing out under thermal loss ...the direct drive alternator would have less loss IMO but I am happy to except that there is more than one way to skin a cat.

I am not sure why you brought up the frequency example..all the equipment is rated to "produce" 50Hz the gens diliver 50 hz on the nose @ 220v with a voltage tolerance of +/- 5%

The outback inverters output and synchronise between 45 and 55hz. If they cant synch in that frequency range they dont output...

Regards

[vawtman]

Start building and report back NEO.

 If you run into problems along the way just ask.Lots of help from great guys.

Have fun

[jimjjnn]

   wouldn't it be cheaper to stay tied to the grid rather tahn running 3 gen-sets ?

[NEO]

Hi Jim,

      I make my own bio diesel from reclaimed resturaunt fat which I get for free powers my old oil fired boiler and all my vehicles and gens with just enuff to spare to suplement my brothers family. Anything to avoid paying the "Man" :-)

Regards

[Nando]

The procedure to synchronize one or more generators is not the problem, is to keep the generators (In your case) in synchro for long time .

This reason plus others is why I do not try to suggest the steps or the way to do it.

So, I prefer to play complete ignorance !!!

Nando

[NEO]

Hi Nando,

        Could I ask why you perceive it would be difficult to keep them in phase?

They can get into trouble for a number of reasons not least of which I will put below. But generally speaking once they are engaged together they cant by themselves get out of phase. In fact the very action of joining them pulls them into identical alignment. This is where the opportunity for damage arises. One gen under load will forcibly pull the lighter loaded gen into alignment or worst case scenario destroy the armature and the bearings of the device you are trying to get in synch, especially if trying make a connection with them 180 Degrees apart!

The common problems are below; anyway just for reference. Each is easily addressable and in all cases damage preventable. Awareness is necessary as with all things from moving rotors to big NEO magnets you just need to know what can or will happen under different conditions, then figure away to avoid the dangers.

One generator failing, if one engine fails because its out of fuel or the oil pressure switch cut off is activated, the alternator of the working unit will attempt via the stallled alternator to drive the stopped engine in order to preserve the phase synchronisation.  This will in turn burn out one or both generators and if the engine is low on oil, damage the engine also.

Resonance-induced hunting, the phase synchronisation between the two alternators is or becomes elastic. If the governor on one engine is not functioning correctly the frequency of hunting will increase and then it begins to resonate with the electrical coupling, the generator will then start to do some heavy duty searching to obtain the correct RPM to drive the load. This can result in the engine coming to a stop and in turn will cause the other alternator to drive the stopped engine the same as above.

Unequal voltages, this will cause a heavy circulating current to flow between the alternators. Causing overheating and excessive load on one or both generators.

Unequal voltage slope, one alternator regulates the voltage compared to the load demanded better than the other. Same result as above but varies with load.

Unstable voltage regulation, for generators that use electronic voltage regulation particularly with brushless designs, also the regulator may not handle the new dynamics and either fails or oscillates.  This can damage the control and field windings and the other alternator.

With one exception here the alternators cant get out of phase and any attempt or occurance to do so is very strongly resisted by one or all connected alternators....to distruction if necessary, presuming the appropriate safty measusres have been ignored!

Kind regards.

Neo

[Volvo farmer]

I think you are a lot smarter than me and will gain no valueable information from my posts. It seems like you already know a lot more than I do as to how to synch three generators at the same time. I wonder about this though... If the lights are flickering while you're synching the waveforms, what are the satellite modem and the television and the DVD player doing?

I think I realize what you're trying to do now, and I do not think it is impossible. Perhaps you will succeed, despite the naysayers on Otherpower. Sorry I can't be of more help, I'm just plodding down the trail of those that have gone before me. I wish you the best and encourage you to post your results of your experiments here so that others may benefit from your experience.

[thefinis]

Well most of these guys are way more informed than I am but it seems to me that your tiered system might work but not quite the way you have it laid out. Most of your load will be during certain periods of the day if your house is anything like mine. First time period is when folks wake up to the time they leave for work and school. Second is when they arrive back from school and work till bed time. During these peak use periods use the diesel genset and kick the inverter off line. Have a charger for the battery bank that can be turned on if needed. During off peak times use the inverter and the battery bank. Anytime the battery bank is too low or the demand is too high for the inverter the genset will need to kick on and the inverter should be kicked off. I am assuming that the inverter can pull from the battery bank faster than the bank is being charged under normal circumstances. A large water heater could be used for a dump load.

okay now I have a question will an outback gridtie inverter push power into a home grid powered by a small genset without major problems? There could be times even with the above setup when the battery bank is recieving power and the bank is full but the inverter is not able to keep up with the demand.

Your idea of using two gensets is out of my league but I do understand what you are saying. It would seem to me that a second induction genset would work better than what you are wanting to try. It would auto regulate itself to the homegrid. One problem I see here is the idea of trying to conserve energy by using two smaller gensets instead of one large one. It would seem like you would just double the upkeep and the problems without a real gain in efficiency. Usually bigger means better, more efficient, and longer lasting. Diesels like long run times and hate cold starts.

My two cents is to spend the money to get a nice diesel genset capable of running the house at peak load. It will provide all the electric power and all the hot water you can use and probably heat the house in the winter to boot. Now add the battery bank and an inverter sized to run the house in the off peak periods with a charger run off the genset. Now add the wind or solar or both to charge the battery bank and streach the time the house can run off the bank. A nice big genset should make clean enough power that the gridtie inverter may not have problems with the homegrid. I don't know how the gridtie inverters handle when the power goes out and then comes back on but it is something I would look at very closely.

Good luck and it is a goal worth aiming for.

Finis

[Countryboy]

At no point did I mention trying to sync wild AC

Oh bullcrap.  You keep saying you want to synchronize the output of all your generators.  The 2 windmill generators are going to produce wild AC.

If you are suggesting that you wanted multiple biodiesel or gas or diesel generators to be synchronous output, then you are ignoring the obvious.  The easy obvious solution would be to get ONE biodiesel generator capable of meeting all your needs.  That way you don't have to screw with multiple machines.

The post was about synching up AC sources particularly my bio diesel generators...I have shown how it can be done and stated another methods one a commercial approach the other a manual approach.

Once again, the simplest solution is getting ONE biodiesel genny capable of meeting all your needs, and not having to screw around with multiple small diesel generators.

If you DID want to run multiple small diesel generators, you would rectify all outputs to DC, and then invert to produce a constant pure AC.

I can already synch my multiple AC generators using the above described method...EXACTLY synchronised for voltage and frequency no deviation at all and load sharing.

If you can already do this, then why are you asking us uneducated amateurs for advice?  What could we possibly know?  I agree with Volvo Farmer - you already know far more about what you are proposing than we do.

I think that you completly missed the point that I have 3 small generators.

I am just looking for someone with a little knowledge of AC control devices to suggest ways of achieving the auto AC synchronisation....the battery bank/inverters from the renewables synchronise! The generators can be synchronised I want to automate the joining of the two systems...this is not rocket science and there is no requirement for deity status to alter the elements!

I think YOU missed the point!  We ALREADY told you the easiest solution is to use all of your gennies to charge the battery bank, and then run the inverter off the batteries.  Forget trying to synchronise the outputs of your gennies.

Yes, synchronous inverters CAN synchronise.  That means they produce the voltage and frequency the line already carries.  The diesel generator is a 'master' and the synchronousinverter is the 'slave'.  You seem to forget that a slave can't serve 2 masters.  If you hook 2 generators to a synchronous inverter, the inverter won't know which generator to be a slave to.  The inverter will fry trying to please 2 masters.

Maybe you don't understand the meaning of a synchronous inverter.  A synchronous inverter does not make the generators match the inverter voltage and frequency.  A synchronous inverter synchronizes its output to the voltage and frequency of the generator's voltage and frequency.

But generally speaking once they are engaged together they cant by themselves get out of phase. In fact the very action of joining them pulls them into identical alignment.

Where are you getting this?  Why can't they get out of phase?  Where do you get the ridiculous notion that the output of 2 generators will be in sync with each other?  A synchronous inverter won't join two generators together.

One gen under load will forcibly pull the lighter loaded gen into alignment or worst case scenario destroy the armature and the bearings of the device you are trying to get in synch*,

Um, once again, how do you propose joining the two generators together?  A synchronous inverter is not capable of doing that.

The closest thing I can think of to anything remotely close to what you are describing, is the process of running single phase current through a 3 phase motor spun in reverse in order to generate 3 phase.

If you were to power an induction motor to spin a generator, the generator's output would be synchronous with the frequency of the power supply to the induction motor.

My advice is to sit back, and read the board for a month or two.  Once you have learned the basics, THEN start asking your questions.

Had you spent a month or two reading the board before asking questions, you would have understood why Nando told you he preferred to play dumb.  I have a difficult time understanding Nando sometimes, due to language translations, but I have learned to recognize that Nando has a wealth of knowledge and experience with setting up non-typical electric generation situations.  The man has probably forgotten far more than I will ever know about electric controls.  When he tells you that he prefers to play dumb, it means that you have asked something ridiculous, and even if it was possible, it is not cost efficient or practical.

[NEO]

opps the formating whent way wrong.......can i delete it ?

Neo

[NEO]

Countryboy,

         It is quiet clear to me that I have made a mistake due to the vociferous nature of your responses. And I do apologise most sincerely. I posted my questions because I believed that there would be some one here who had attempted to do what I wish to do or was interested in the concept.

          I do not have all the answers. My concern is that you highlight comments out of context; this with the greatest of respect is so verging on the appearance of troll like behaviour. Not once have you asked me a question all you have made are self opinionated statements based on a failure of comprehension of what I have been asking or saying. I have re read my original post to see if the questions and premise still make sense.

         I am not sure if I should even address your last post but I feel in someway responsible, as I wrote my own words. Perhaps if I take your formatting approach?

"Oh bullcrap.  You keep saying you want to synchronize the output of all your generators."

              hmmm..ok slight missleading due to terminology. The statement is true and way to broad. The point at which synchronisation occurs is the fundemental difference. I have no intention what so ever tyring to synchronise a diesel generator set and an AC mill at the same point. Might I surgest a slightly smaller hammer to crack the wallnut shell as opposed to a wrecking ball.

"The 2 windmill generators are going to produce wild AC."

               Agreed it is my intention and always was that I should rectify this with inverters, connect them with appropriate charge controllers to a battery bank.

Using grid tie inverters that will synch to a stable reference voltage and frequency...to copy from my original post

     "I am thinking the best way to do this is to trick the inverters I put on the mill/s and the solar panels to thinking they are grid tied by perhaps having a stable "reference" voltage and frequency perhaps supplied from the battery bank."

"If you are suggesting that you wanted multiple biodiesel or gas or diesel generators to be synchronous output,"

              Yes I am, I want to automate my generators starting and synchronising to each other and the bus.

"Then you are ignoring the obvious.  The easy obvious solution would be to get ONE biodiesel generator capable of meeting all your needs.  That way you don't have to screw with multiple machines."

              I am not ignoring it I am trying to find away around it. I can produce the power in the right format and I believe with the appropriate switching technology at a much lower cost than a new generator I can by application or `screw around' as you put it to get the desired result.

"Hombrew" to my mind is all about `screwing around' your phrase not mine, to achieve something that in the case of windmills is available from another source. By your analogy everyone should not bother `screwing around' with a mill when there are other proven and tried techniques that in your opinion are less fuss and less hassle.

"If you DID want to run multiple small diesel generators, you would rectify all outputs to DC, and then invert to produce a constant pure AC."

              1) Why? When a pure constant wave form already exists from the output of the alternators, in fact not only does it exist but aside from the phase angle probably being different the output is identical to the supply the renewable inverters are connected to. Back this up with some facts please ones that can be verified by pointing me in a direction or to someone qualified to validate your opinion.

"If you can already do this, then why are you asking us uneducated amateurs for advice?  What could we possibly know?  I agree with Volvo Farmer - you already know far more about what you are proposing than we do.

                I know it can be done, I do not know the best way to do it, so I am asking.

Hmmm uneducated amateurs...you do your fellow board members a disservice! There seems to be a lot of highly educated people connected to this forum with many experiences from many walks of life. `Flux' and Nando for example seems to have a fine and solid education and experience in electronics and electrical theory. My replies to this thread are to pass on what knowledge I have; in the hope someone interested in this subject will gain from what I have to offer. It's a community thing.

"I think YOU missed the point!  We ALREADY told you the easiest solution is to use all of your gennies to charge the battery bank, and then run the inverter off the batteries.  Forget trying to synchronise the outputs of your gennies."

                This is a (one, simgular) solution....but need to be taken in context, as above at point 1)

"Yes, synchronous inverters CAN synchronise.  That means they produce the voltage and frequency the line already carries.  The diesel generator is a 'master' and the synchronousinverter is the 'slave'.  You seem to forget that a slave can't serve 2 masters.  If you hook 2 generators to a synchronous inverter, the inverter won't know which generator to be a slave to.  The inverter will fry trying to please 2 masters.

Maybe you don't understand the meaning of a synchronous inverter.  A synchronous inverter does not make the generators match the inverter voltage and frequency.  A synchronous inverter synchronizes its output to the voltage and frequency of the generator's voltage and frequency."

                This is the point that you have got ALL backwards. The first line is nearly spot on; they produce a voltage and frequency that as near as damit exactly matches the reference voltage in this case the grid voltage and frequency.

Then it where it all goes horribly wrong for you again with another erroneous statement. There is NO master and slave generator in a synchronous set up by definition they DO NOT exist! and I am not discusing alternators with different power outputs. I don't forget that a slave can not serve two masters because there are not to masters to be served! What is also erroneous in your statement is the inverter will fry! absolute rubbish! A grid tie invert will disconnect itself from the reference source if the frequency or voltage or angular phase, changes beyond the preset parameters that govern its synchronisation in the first place.

If you take two running generators that are synchronised together they will be in phase and they will; all things being equal appear to be one single source of power.

If the two above generators that now function as one and having a stable output voltage and a stable frequency, (and there is no reason they shouldn't) that closely matches the tolerance for the grid tie inverters synchronisation parameters, then the inverters will in turn synchronise to the alternators output adding to the total power available. In the case of a grid tie inverter, it assumes it's connected to the grid and then synchronises with the generator supplied output. Exactly what you said in your last paragraph, and I have never implied differently!

"Where are you getting this?  Why can't they get out of phase?  Where do you get the ridiculous notion that the output of 2 generators will be in sync with each other?  A synchronous inverter won't join two generators together."

                  What exactly is ridiculous here? How exactly do you think a generating company creates enough power to supply demand? It does not have one almighty generator! It has a number that it brings up and synchronises with the ones currently in operation, to supply any additional power demand. The grid then delivers that power from synchronised mixed sources to the homes, where some people have grid tied power generation that then synchronise with the voltage and phase parameters seen at the point of delivery from the grid. In fact there is more the same grid also allows the connection to other power generation companies not afiliated with the first whose generators also have to be in sync with the grid prior to connection. This is the established practice, this is the way it is done.

You are correct an inverter will not join two generators together. I never said differently!

"Um, once again, how do you propose joining the two generators together?  A synchronous inverter is not capable of doing that."

                  At the risk of repeating myself. There are two methods known to me one a manual interaction which I have detailed the process of and use, the other is with what's called a synchroscope. I do not want, nor can I afford a synchroscope based upon those I have found that will suit my needs, hence the whole reason behind this post "A way to do it automatically with out a commercial synchroscope"

Your last sentence is again correct that an inverter is not capable of doing that and again nor did I suggest that it could.

"The closest thing I can think of to anything remotely close to what you are describing, is the process of running single phase current through a 3 phase motor spun in reverse in order to generate 3 phase."

                   This statement is another statement of yours that again highlights your yet unrecognised desperate need to ask more questions and read the replies more diligently. Your thought/response here is so far off base and erroneous it might as well be in response to how to plane a piece of wood. I use one of these to supply my 3 phase milling machine but nowhere does it spin in reverse! It's called a rotary phase converter and works on the principle of induction to generate a phantom 3rd phase from one of the windings that is naturaly in phase with the source single phase supply.

Here is an easily comprehendible page on how it does work and it has even got some diagrams

http://www.metalwebnews.com/howto/ph-conv/ph-conv.html

"If you were to power an induction motor to spin a generator, the generator's output would be synchronous with the frequency of the power supply to the induction motor."

                    completely irelevant to this post.

"My advice is to sit back, and read the board for a month or two.  Once you have learned the basics, THEN start asking your questions."

                     I think you ought to take your own advice before you cause your self further embarrassment or make any further erroneous statements that someone might take for granted as fact and have a mishap with!

"Had you spent a month or two reading the board before asking questions, you would have understood why Nando told you he preferred to play dumb.  I have a difficult time understanding Nando sometimes, due to language translations, but I have learned to recognize that Nando has a wealth of knowledge and experience with setting up non-typical electric generation situations.  The man has probably forgotten far more than I will ever know about electric controls.  When he tells you that he prefers to play dumb, it means that you have asked something ridiculous, and even if it was possible, it is not cost efficient or practical."

                      I am not going to enter into a verbal rant with you.

I have proven categorically that it is possible and that it is likely to be very cost efficient with the control devices I have in mind and a little help..compared to either a new generator set or the cost of synchroscopes I have seen.

As for interpreting Nando's reply, he posed a situation very similar in concept to what I am talking about, but declined not to comment further because it was beyond his field of expertise. At least that was my interpretation and will remain so until he voices different. I am confident that he can a) speak for himself and b)re address any miscoception I may have on his thoughts! with out you speaking or asuming for him. Thats just plain rude!

Quite frankly you need to read more carefully and digest what is written or proposed and then think on it for a while.....then ask questions if you are unclear as to the concept being proposed. You also need to stop making assumptions and making wildly defamatory and erroneous remarks. It will so help the perception you have given to me and others I am sure, that you are the resident forum troll.

If you do not understand something I have said ask and I will try and clarify but I will not address another one of your posts if it comes in the same style again and I will also seek admin advice.

update.....

I was just re reading this for accuracy and I have to thank you, you  have helped me with one thought, not the automation or its feasibility but with, what will happen to the inverters when a generator starts.....it will disconnect itself from the reference voltage But it will reconnect as soon as the generator settles down. . Having said that if a single generator start and is synchronised with the reference voltage the same voltage the inverter is synchronised to before the breaker is closed then nothing potentially adverse will happen because all the units on in synch. Starting another generator and synchronising that will have no further impact because it will not be delivering any power to the bus until it is synchronised with the bus....

Thanks, now how to automate the starting and synchronisation part.

Neo

Sorry its been long response everyone but the truth will out.

[Countryboy]

How exactly do you think a generating company creates enough power to supply demand? It does not have one almighty generator! It has a number that it brings up and synchronises with the ones currently in operation, to supply any additional power demand.

If this is your goal, then I propose you do it the SAME way the utility grid does it.

Each and every single generator will have a synchronizer to get it to match the grid voltage and frequency.  If you have a windmill, you will need variable pitch blades, going into a gearbox, with high dollar electronic controls, in order to keep the alternator producing at a constant frequency and voltage.  If you use a diesel generator, you will need a RPM governor which can keep RPMs constant, regardless of load, just like the utility companies use.

Why? When a pure constant wave form already exists from the output of the alternators, in fact not only does it exist but aside from the phase angle probably being different the output is identical to the supply the renewable inverters are connected to.

Since when do homebrew windmills produce a pure constant waveform?  They don't, and that's part of what you are overlooking.  Homebrew gennies put out wild AC, which is not pure or constant.

[NEO]

Afternoon Countryboy,

          Your doing it again oh well...

"Since when do homebrew windmills produce a pure constant waveform?  They don't, and that's part of what you are overlooking.  Homebrew gennies put out wild AC, which is not pure or constant."

           For the love of God! I NEVER SAID THEY DO!! I said REPEATEDLY they should be connected to a battery bank via rectifiers and inverters with charge controllers...then the output waveform from the inverter/s will be a pure stable wave form..... as you move along the chain of devices you travel from an intermittent unstable AC wave for through rectification, through an inverter and the output on the other side is a stable wave form voltage and frequency...but then you know this already...why do you assume that I do not know this?

"Each and every single generator will have a synchronizer to get it to match the grid voltage and frequency.  If you have a windmill, you will need variable pitch blades, going into a gearbox, with high dollar electronic controls, in order to keep the alternator producing at a constant frequency and voltage.  If you use a diesel generator, you will need a RPM governor which can keep RPMs constant, regardless of load, just like the utility companies use."

            This is hard work but we are getting there mate, I can feel it in my water. It is not necessary to have a complicated mill with variable pitch nor are high dollar controls necessary. You obviously missed the line in the post about the generators having droop mechanical governors. There purpose is to adjust engine RPM based on load. They permit load balancing across the sets. As both alternators receive equal quantities of load then they both adjust RPM to compensate in unison. still maintaining I hasten to add a stable output.

Now what we need to do is to think smaller...take ANOTHER look at the proven manual process for the synchronisation of engine driven alternators and look for ways that, the process can be automated using readily available off the shelf relays that sense ROCOF/Vector shift and under/over voltage sensing and under/over frequency sensing and other cheap techonology like CT coils and AC contactors.

I honestly do admire your tenacity.

Neo.

[Nando]

Neo:

I am always worried when some ideas are presented. to this group, by people that with just the way that the question is presented, the member indicates limited capabilities in all the technical areas of electrical systems.

I see that you may have the technical capabilities to perform phasing.

The problem with large systems is that the systems are time stable and once in synchro it is easy to keep time stable.

For smaller systems with much smaller hydrocarbon fuel engines with low time constants, the correction becomes a bit complicated and a bit massive in dynamic control.

My suggestion is for each generator to have a massive flywheel for stability, then the generator itself have the ELC's and the sharing current transformers in a matrix for power equalization.

If some of the generators can be Induction motors then it is easier to couple them, bias them from the master power with proper tracking of the Power Factor and peak power limitations to avoid a possible oscillatory conditions due to the master being overwhelm by the slaves greater power, easy the power sharing including capacitors with each added SLAVE.

Fast PF detection and Slave cut off may be required to avoid a quasi - massive internal shorts with out of phase generators.

This is an interesting project for me just to make them phase initially and long term under variable loads.

And Thinking a bit more:For small systems, the slaves should be INDUCTION MOTORS AS GENERATORS for a more natural an easier power addition, with current sharing transformers to get the PF and the % of current sharing as desired.

Nando

[NEO]

Hi Nando,

        The units have mechanical governors and these are easily trimmed and very responsive to the slightest change in load. When two are coupled and one engine is mechanically retarded then the other instantly increases rpm by what I can only imagine is the difference needed to accommodate the load. But that said I believe that is an electrical response. Having non linked governors' means that both are able to try and match the alternator demand independently. A good thing because if there is a change to one alternator you only want its coupled engine to adjust itself and not the engine of its counterpart..

I can't speak for larger alternators with a wider load margin between minimum and maximum delivered power versus load as they may have a different dynamic. However; with smaller units 5Kw when one is running under say 75% of load (lets call it number one gen) and the other (number two gen) is then started, engine speed is brought up to match closely #1 then using the synchronisation process the alternators are paralleled by closing a breaker. At that point assuming that you are not holding #2 at an artificially high rpm both engines simultaneously shed RPM and share the load, and near as I can tell both will maintain the same RPM.

Just by observation no one unit seems to lead or have priority. Impeding the airflow into the engine at the filter causes one to slow and the other to speed up and vice versa. Increasing the RPM of one unit at the throttle also causes the other to speed up but I think in both cases this is due to the one alternator driving the other in an attempt to balance the load.

 If I have this right and I think I do. If an attempt is made to pull one out of step a current develops that circulates between the machines this current either speeds up the slower lagging machine or slows the faster or leading machine thereby acting to prevent either of the machines from pulling out of  synchronisation. I believe it's actually called the synchronising current. I am willing to stand corrected on this. I will Google that to, to check.

However; when the load or demand changes both units respond almost identically, I stress almost. One does seem to be slightly faster for a brief moment and then they seem to settle to the new load again at the same RPM. As a note though it appears to be random which unit is briefly faster, this I suspect is due the synchronising current constantly changing fractionally the armature position by a very small amount either  faster or slower temporally compared to its sister.

I have yet to see them behave in any manner other than expected even when there are three together, and I have not seen a destabilisation in the voltage or frequency, but that is only a four hour time period and the load was relativly stable.

There is no electrical sensing or sense's disconnects at present and I strongly agree its definitely something to include in the circuit design at the earliest opportunity to protect against any untoward condition developing either mechanical or electrical.

Regards

Neo

[Nando]

FIRST:

Venezuela and Paraguay are about 2000 kilometers apart

Second:

The Hydroelectric plant you refer to, is in the Brazil/Paraguay borders

Third:

Rectification is very in-efficient, in-practical, what is done is that some of the generators are slowed down to generate 50 Hz

Paraguay is a country of about 6 millions, so most of the power is for Brazil and Argentina since it does receive as well.

~~~~~~~~~

Several member have been hitting this guy and his message because they can not understand why such electric set up.

Examine what he really has in mind and liberate yourselves from the idea of only Wind generation.

Nando

[robl]

I've quite enjoyed all the churn over this topic. some of the theoretical musings have also been quite worth reading.

Might as well throw my two cents in, from ( I think) a more practical perspective. I have about 20+ years personal experience with off-grid power production, storage and distribution. I am very familiar with a multiple genset approach. However, every single one of these setups (up to three, usually Yanmar/Deutz/Cat with Stamford lashups)were designed to be independent from the get-go. That way one glitch doesn't take out the entire setup. Individual banks of loads can be powered up and down as needed (via timers even), optimizing efficiency, and reducing noise. Thhey may not alll even be the same size - the smallest, quietest unit may be the one that runs the lights all night long, while the bigger units cool the freezers, run the pumps and compressors during the day.

Regards

Rob

[Volvo farmer]

Dude, he doesn't want to synch windmills, he wants to synch diesel generators.

[Countryboy]

Nando,

  I stand corrected about the countries involved.  The Itaipu Dam is on the Parana River, between Brazil and Paraguay.

However, I was correct that the 50 Hz AC generation from Paraguay, which is sold to Brazil, is rectified into DC, and then inverted back to AC at 60 Hz, which Brazil uses.

Brazil built two transmission systems.  One carries the 60 Hz AC produced on the Brazil side of Itaipu at 750 Kv.  Brazil purchases some 50 Hz AC from Paraguay.  It is rectified into 500 Kv DC current.  The 500 Kv DC current is then inverted into 60 Hz AC at Ibiuna, right outside of Sao Paulo.

http://www.solar.coppe.ufrj.br/itaipu_ee.html

If rectification is so inefficient and impractical, why are 6000 Megawatts of 50 Hz AC rectified into DC, and then inverted back into 60 Hz AC?

[Flux]

Automatic synchronisers have been available for many years. I have met them but was never involved and have no idea of the circuitry.

With modern electronics it should not be difficult but I have never had need to give it thought.

Smallish diesel generators are not as easy to synchronise as large turbo alternators.

I would be reluctant to try it with single phase and even with 3 phase I would only try it with identical machines or machines intended to run in parallel.

As you say you need similar governor characteristics to share load. To be sure of stability you need quadrature droop compensation on the AVRs to share reactive power.

It generally works better with one generator bigger and with more precise governors and no quad droop running as a master and sync the others on to it.

It may be simpler to use one synchronous alternator as a master and to add other induction generators, perhaps with a bit of power factor correction.

I suspect that to automatically synchronise you will need a motorised control on the speeder spring of the alternator you wish to sync. A circuit will cause that motor to bring the speeds to very close to the same value, then a phase sensing circuit will close the breaker when they are in phase.

Attempting to do it without equalising the speed will probably result in tripping even if you can hit the in phase point.

Good luck.

Flux

[maker of toys]

to autosync gens:

place a resistor/s of moderate value in the place of the lightbulb/s in the manual method; say 10kohms or so. choose numbers that make you comfortable with the currents and wattages involved.

connect a bridge rectifier across the resistor/s, with the assumption that the resistor will be the AC source for the rectifier.

place a capacitor across the DC outputs of the recifier. put a bleed resistor across the capacitor such that you wind up with a 'no input' discharge time that makes you comfortable. 1/2 second or more would be my choice. . . your milage will certainly vary based on your grasp of, and comfort with, the amount of frequency mismatch  your equipment can stand.

the voltage across the capacitor will now drop as the sources get closer and closer to phase, reach a low point when they are in step, and rise again as they fall out of step.  you can use a voltage divider in place of a single bleed resistor to bring the voltage across the capacitor into line with what integrated circuits can manage.

the low-voltage condition across that capacitor can be used with suitable sensing to drive a transistor-contactor cascade to switch the new source into the microgrid.

the basic method requires some operator attention, mainly to feather the throttle on the 'new' source until the hardware is happy and pulls in the contactor.

alternately, an ADC and a microcontroller can watch the voltage across the capacitor, send speed correction signals to the governor of the 'joining' source, and proceed as above. the 'Ball bearing' sort of RC servos make good end effectors for the throttles of engine driven equipment;  small gear-head motors or stepper motors work well, too.

sensing can be as simple as an optocoupler or as complex as an ADC input into the computer console that runs the entire house. . . the programming of the uController or computer can, of course, be as complex as you like, and can easily manage the start/run/cool/stop behavior of the whole complex. . .  as well as things like time balancing, maintenance reminders and the control of co-gen heat or cooling to the structure. It's all a case of how much programming you are willing to do. . . .say hello to HAL?

in any event, use a contactor rated for the full output of the gen (duh?), and provide 'semiconductor' type fusing on the output of every energy source in case of serious wrongness. These very fast fuses will probably save an alternator, but I wouldn't count on them saving an inverter. . . so the inverter doesn't get to be the 'master' without some additional thinking by an engineer you pay to get it right. . . . free advice being worth every penny you spend.

have fun!

-Dan

[NEO]

Hi guys,

       They say a picture says a thousand words, I feel I have spent a long time trying to explain only to be miss understood. So I have done a quick pencil sketch of what I am trying to achieve.

There are something's I expect you to take for granted;

1. This is not a circuit diagram more a block representation.
   
2. Safety fusing or circuit protection is not drawn in and in many cases it's to be taken as inherent or implied at different points of the diagram. Common sense stuff.
   
3. The engines and the exhaust temperatures will be exploited during operation to recover heat via heat exchangers to supplement space and or water heating.
   
   

        Now this is where it may or may not come all unstuck and have to be re worked (something I fully expect will need to happen). You will notice what I have termed as a "reference Inverter" this one is on all the time directly connected to the Battery bank. Its purpose is to output an "as stable as possible" voltage and frequency on to the bus bar in order to give all the intermitant souces something stable to synch up to.

The idea is the GTI box's (grid tie Inverters) will view this "reference" frequency and voltage as being the grid and in turn synch to that voltage and frequency and deliver power to the bus bar.

The Auto start/Stop box senses current and starts or stops the engine based on load or demand as well as duration i.e. when the current reaches X for A minutes start  gen one when current reaches Y for B minuets start gen 2 and when current reaches Z for C minutes start gen 3.

As for stopping, when current values are detected to be falling and reach for example Y minus 5 for A minuets disconnect gen 3 from the bus bar and run for D minutes to cool down then stop the engine.

The synch Box does what is says on the tin synchronises a started running generator to the bus bar by closing a contactor (C) at the appropriate moment. It will also disconnect the generator from the bus bar if an abnormal voltage or frequency is detected.

Finaly the bus bar delivers power to the Distribution Board and to the different loads.

Least that's the Idea

Dan thanks that was the sort of reply I was expecting from the very beginning :-))

Thanks for your comments and thoughts, please keep em coming.

Kind Regards ALL

Neo

[NEO]

Dan, Flux Rob,Nando, etal,

Here is a retyped text from the alternator manual, think I need to RTFM more frequently :-)

6.2 PARALLEL OPERATION

Understanding of the following notes on parallel operation is useful before attempting the fitting or setting of the droop kit accessory. When operating in parallel with other generators or the mains, it is essential that the phase sequence of the incoming generator matches that of the busbar and also that all of the following conditions are met before the circuit breaker of the incoming generator is closed on to the busbar (or operational generator).

1. Frequency must match within close limits.
   
2. Voltages must match within close limits.
   
3. Phase angle of voltages must match within close limits.
   
   

A variety of techniques, varying from simple synchronising lamps

Neo comment:- This is what I was doing as per the manual synch description I posted in this thread)

to fully automatic synchronisers, can be used to ensure these conditions are met.

Important !

Failure to meet conditions 1, 2, and 3 when

closing the circuit breaker, will generate

excessive mechanical and electrical

stresses, resulting in equipment damage.

Once connected in parallel a minimum instrumentation level per generator of voltmeter, ammeter, watt meter (measuring total power per generator), and frequency meter is required in order to adjust the engine and generator controls to share kW in relation to engine ratings and kVAr in relation to generator ratings.

It is important to recognise that

1. kW are derived from the engine, and speed governor characteristics determine the kW sharing between sets.
   
2. kVAr are derived from the generator, and excitation control characteristics determine the kVAr sharing. Reference should be made to the generating set manufacturer's instructions for setting the governor controls.
   
   

Neo comment :- I do not have the  droop accessory--- droop is by a mechanical droop governor --- a small RC servo could manipulate this??.. Rob?.

6.2.1 DROOP

The most commonly used method of kVAr sharing is to create a generator voltage characteristic which falls with decreasing power factor (increasing kVAr). This is achieved with a current transformer (C.T.) which provides a signal dependent on current phase angle (i.e. power factor) to the AVR. The current transformer has a burden resistor on the AVR board, and a percentage of the burden resistor voltage is summed into the

AVR circuit. Increasing droop is obtained by turning the DROOP control potentiometer clockwise.

The diagrams below indicate the effect of droop in a simple two generator system

Generally 5% droop at full load current zero p.f. is sufficient to ensure kVAr sharing. If the droop accessory has been supplied with the generator it will have been tested to ensure correct polarity and set to a nominal level of droop. The final level of droop will be set during generating set commissioning.

Kind Regards

Neo