50Hz 230 volt power in a 60Hz world

[weressl]

I was trying to be nice.........

I am not under such gentlemanly obligation, I am not British. :bye: I mean I should be, but somewhere along the line I stopped giving a flying.....:rotflmao:

 

[kwired]

In this particular instance, he has little or no useful knowledge.

Grid-tied systems have requirements that are intrinsically hard to satisfy because the equipment is designed very carefully to NOT connect to something that isn't the electric grid.

The indication that he had no clue was suggesting that the 50Hz power be rectified and then converted back to 60Hz with a 4 quadrant VFD. That =can= be done, but controlling how much power is converted becomes its own problem. In particular, there still has to be a 50Hz signal that behaves sufficiently like the electric grid (or is stout enough that it can't be "moved" by the anti-islanding logic in the inverter) to keep the inverter from disconnecting.

A far simpler solution, and one that's guaranteed to work is to set the system up for AC coupling. Inverters that can AC couple are readily available and solve all the problems with a minimum amount of equipment and handle the change in the direction the power is flowing very automatically. They're also listed for the purpose and meet the appropriate UL and IEEE standards.

Why are you asking questions if you already have (or think you have) the answers? If you disagree with something give us logical reasons and don't just tell someone they don't know what they are talking about. He may not be all up to speed specifically with PV systems, but he does understand electricity and especially inverters.

 

[jim dungar]

Enough!

The discussion seems to be headed toward personal attacks. Everyone needs to take rest or risk the closing of this thread.

 

[SolarPro]

A far simpler solution, and one that's guaranteed to work is to set the system up for AC coupling. Inverters that can AC couple are readily available and solve all the problems with a minimum amount of equipment and handle the change in the direction the power is flowing very automatically. They're also listed for the purpose and meet the appropriate UL and IEEE standards.

You probably void your own product warranty in the process. But if it works, you could be the first company to plant a flag in ac coupled micro space.

 

[Besoeker]

Why are you asking questions if you already have (or think you have) the answers? If you disagree with something give us logical reasons and don't just tell someone they don't know what they are talking about. He may not be all up to speed specifically with PV systems, but he does understand electricity and especially inverters.

Thank you for that,kwired.
And if the issue is converting 50Hz to 60hZ I perhaps ought to mention that the last couple I did were rated at 5MVA, 13.8kV output.
I accept that I still have lots to learn and that there are gaps in my knowledge. But, after about 45 years dealing with electrical equipment and particularly power electronics at least some of it was bound to stick.

 

[iceworm]

...A far simpler solution, and one that's guaranteed to work is to set the system up for AC coupling. Inverters that can AC couple are readily available and solve all the problems with a minimum amount of equipment and handle the change in the direction the power is flowing very automatically. They're also listed for the purpose and meet the appropriate UL and IEEE standards.

tall -
I had to look up "AC coupled". Is this what you have in mind?
http://lses.org/version1/AC%20Coupling%20WHT%20Paper%20(2).pdf

If so, the output to the utility is 50 Hz. I read all nine pages. It appears you are looking for a method to use the excess energy to power 60hz equipment - not 50hz.

Or perhaps you were thinking the second inverter (the one tied to the mains) the be a 50hz input from the micro inverters and then 60hz output to the utility. I did not see any inverters that were "readily available" that will do this.

We have a growing amount of 50Hz 230 volt power (single phase of a 230/400 volt system) that's being produced at the office. Right now it is all being turned into heat courtesy of a rather large dump load.

The way things are wired right now, there is a several KW 50Hz power supply that is providing a grid reference to what I think is a 2 or 3KW solar array that is powering 50Hz microinverters. The microinverters are back-feeding the supply, which has its output paralleled with the dump load. So, if the sun isn't shining, the dump load is turning most of that 50Hz power into heat. And if the sun is shining, even more of it is turned into heat.

What are the code issues that might be associated with actually =doing= something useful with that power?

When the EE's were originally setting up the testing system, my proposal was a quad stack of OutBack gear -- a twin stack of 50Hz grid-interactive inverters, and a twin stack of 60Hz grid-interactive inverters, with batteries in the middle. Controlling the output of the 50Hz array with a contactor, with the coil power from the 60Hz grid, would have been fairly easy.

It certainly sounds like you are saying the existing test setup has micro inverters driving into a stable 50hz grid that has an integrated load bank. Or you are saying the micro inverters can drive the load bank directly and don't need a stable 50hz grid.

Which might it be? There has been enough wobbling I can't tell what the equipment is capable of and what you are trying to do. The posts leave me uncertain.

ice

 

[iceworm]

...I'm not completely privy to all the decisions, but my understanding is that the batteries were the deal-breaker. ...

...It's a lot easier and cheaper to just turn the electricity into heat -- I think we average 3 to 5KW on a 24 hour basis. That's $0.50 / hour, or $12 / day at residential energy rates. ....

If it is just the case of the price of a battery bank, I'm wondering just how much money is available. $12/day, ~$4000/year, test setup to be abandon, maybe 3 year pay back - not counting interest, maybe $12k. That's not much - take off 2/3 for engineering and installation labor - gives $4000 for equipment.

It certainly is a lot easier to turm the energy into heat - the company could easily be spending multiple $10K/day for product development. They need to stay focused, get done, stop the cash hemorage, get in production, and get selling.

I'm not surprized you can't find any corporate interest.

But, if you do get some interest, perhaps suggest an ultra capacitor instead of a battery bank. Russian desgn/mfg, Canadian company selling them last time I looked (couple of years ago). Just an idea.

ice

 

[iceworm]

Whoops - fat fingered the keyboard - duplicte

 

[tallgirl]

You probably void your own product warranty in the process. But if it works, you could be the first company to plant a flag in ac coupled micro space.

One of my objectives is to get the company to officially support AC coupling. Most of my background is off-grid and grid-interactive systems with batteries. Working for a microinverter manufacturer means I'm usually at odds with the marketing and engineering staff ...

The usual approach to AC coupling with grid-tied inverters is to disclaim support -- that's what our main competitor does, they say the warranty will be voided if that other brand's inverters are AC coupled.

 

[tallgirl]

tall -
I had to look up "AC coupled". Is this what you have in mind?
http://lses.org/version1/AC%20Coupling%20WHT%20Paper%20(2).pdf

If so, the output to the utility is 50 Hz. I read all nine pages. It appears you are looking for a method to use the excess energy to power 60hz equipment - not 50hz.

Or perhaps you were thinking the second inverter (the one tied to the mains) the be a 50hz input from the micro inverters and then 60hz output to the utility. I did not see any inverters that were "readily available" that will do this.

This thread was originally posted to the NEC forum, then moved here. The =original= intention was to find out what code impediments there are to directly utilizing 50Hz 230VAC power within a building that is otherwise 60Hz. I think the migration from the NEC forum to the PV forum has been less than beneficial.

When the applications crew was originally discussing the array setup, my suggestion was to use a 50Hz OutBack inverter to provide the grid signal and AC couple to the 50Hz microinverters. That inverter would charge a (small) battery bank -- DC coupling, as it were to the 60Hz inverter. Excess power going into the batteries would then have been sold back to the grid by a 60Hz inverter. That, as I noted earlier, was rejected in favor of the current setup.

It certainly sounds like you are saying the existing test setup has micro inverters driving into a stable 50hz grid that has an integrated load bank. Or you are saying the micro inverters can drive the load bank directly and don't need a stable 50hz grid.

Which might it be? There has been enough wobbling I can't tell what the equipment is capable of and what you are trying to do. The posts leave me uncertain.

ice

The current configuration is what you described at first -- a stable 50Hz supply feeding an array on the roof with a paralleled load bank. The microinverters can't operate, with the current firmware, without an external 50Hz signal due to anti-islanding requirements.

 

[iceworm]

...The current configuration is what you described at first -- a stable 50Hz supply feeding an array on the roof with a paralleled load bank. The microinverters can't operate, with the current firmware, without an external 50Hz signal due to anti-islanding requirements.

Curiousity about the existing test setup: What is providing the stable external signal 50hz signal?

...A far simpler solution, and one that's guaranteed to work is to set the system up for AC coupling. Inverters that can AC couple are readily available and solve all the problems with a minimum amount of equipment and handle the change in the direction the power is flowing very automatically. They're also listed for the purpose and meet the appropriate UL and IEEE standards.

Of course, AC coupling (as currently defined here) to transfer power from 50 hz micro inverters to a 60Hz system is not possible, and you didn't like any of the profered solutions, so your original queries of how to use the waste heat power is no longer the topic?

Ok

So what is your prefered topic? The thread is mildly interesting - but some focus would be good.

ice

 

[iceworm]

...What are the code issues that might be associated with actually =doing= something useful with that power?

The OP did pose a lead to an interesting problem. Code issues are no different than most ordinary building/equipment - trivial. The interesting part is how to do it. Lots of suggestions on power electronics with 4 quadrant control - all certainly interesting and as you noted, all certainly with probable waveform distortions.

I'm thinking an elegant solution is brute force - copper, iron, and not AC coupled nor DC coupled, but mechanically coupled.

Consider a 12 pole synchronous motor coupled to a 10 pole synchronous generator. It would provide a stable 50hz external reference for the micro inverters. As the inverters came up, the power angles change on the generator and motor and it would automatically pump power back into the 60Hz utility, serving both as load dump and waste energy recovery. It has near perfect sine wave outputs (minor issues with generator winding pitch that likely wouldn't matter here).

Certainly stone-age compared to solutions from bes, wer, k and others. - but oh so elegant. Maybe even better conversion efficiency than the power electronics.

But I couldn't bring it in for the money you have available either.

ice

 

[tallgirl]

Curiousity about the existing test setup: What is providing the stable external signal 50hz signal?

An over-sized power supply fed from the grid. The dump load is large enough to consume everything that could ever be made by the inverters, just to avoid having the power supply back-fed. If more inverters are added, the amount of power from the grid will have to go up as well.

And yes, the motor-generator would be an awesome solution.

 

[GoldDigger]

An over-sized power supply fed from the grid.

So the power supply provides the low "grid" impedance that the GTIs need to see, as well as the stable frequency?
You adjust the dump load as needed to make sure that some fraction of the power comes from the supply, or do you just set the dump load to the highest possible output from your GTIs and let the power supply make up the difference?
If you do come up with a way to transfer the dumped power back to the 60 Hz grid, you will need additional regulatory circuitry to control the amount of power backed, or else set it up for a constant maximum back feed, just as you would use a constant high power dump load.
I could see this being a problem with the MG set. (And the MG itself would not necessarily be stable enough and appropriately UL listed for grid feed.)
And if you go with a 50Hz to DC, DC to 60 Hz combination with the minimum required battery in between for stability, you would have to work hard to get the 50Hz to DC conversion running with a low distortion PF to avoid requiring a high compensating distortion current from your reference supply.
Unless you are generating a really substantial amount of power from your 50 Hz GTI, I am not sure that it would be economical, regardless of the gut aversion to wasting the power.

 

[hillbilly1]

............And yes, the motor-generator would be an awesome solution.

Really.............seems like something similar was suggested early on in the postings, just not selling it back to the POCO, utilizing the power on site.:roll:

 

[iceworm]

I'm assuming that this is part of a testing process, so you need a consistent load, otherwise I would say power a motor/generator set, or something similar to convert it back to 60hz to recoup some of the power loss. Otherwise, plenty of hot water for the cafeteria?:lol: On a serious note, maybe a steam turbine/generator set? Don't know how much heat you are producing, so I don't know if that's viable. I have heard of "Tornado" type generating stations that use the heat rise to spin a turbine, which should have smallest effect on the load bank.

Really.............seems like something similar was suggested early on in the postings, just not selling it back to the POCO, utilizing the power on site.:roll:

Yes you did - in post 2. Sloppy me. I try to catch and credit all of these.

In my defense, I didn't see the concept of coupling a synchronous 10 pole gen to a synchronous 12 pole motor to capture the 50/60hz conversion, nor the idea of running the power transfer bi-direcction to both cover the stable 50hz source to allow the micro inverters to start as well as provide a load dump for the micro inverters that seamlessly transfers the power to the 60 hz utility.

ice

 

[iceworm]

...If you do come up with a way to transfer the dumped power back to the 60 Hz grid, you will need additional regulatory circuitry to control the amount of power backed, or else set it up for a constant maximum back feed, just as you would use a constant high power dump load.
I could see this being a problem with the MG set. (And the MG itself would not necessarily be stable enough and appropriately UL listed for grid feed.) ....

For a synchronous set, little regulatory circuity needed. Set both sides up for a 1.0pf. Power should transfer di-directionally. Which ever side has the leading power angle will transfer power to the other side. That's the beauty of what one might call mechanical feedback. Gets rid of a cubic foot (or cubic yard) of electronics.

I'm not sure where the stability issue comes from. Synchronous motors are as frequency stable as the utility line frequency is. We are talking "Locked in Step"> Now that I think about it, use synchronous motors on both sides. They will work fine as a generator when the power angle reverses.

As for the UL, that is just a matter of getting their MG spec - if there even is one. If not, use recognized components (which motors generally are) and build under NEC 409. And since this is product development testing, may not even need to be listed. Install under NEC 590

...Unless you are generating a really substantial amount of power from your 50 Hz GTI, I am not sure that it would be economical, regardless of the gut aversion to wasting the power.

Of course it isn't economical - that was covered several posts ago. The project can't even afford a battery bank.

I personally don't have an aversion to wasting energy. I have an aversion to wasting money or time. Using energy to save time or money is an accounting decision. Excepting Safety, Environmental, or Regulatory, if the project does not have an acceptable ROI --> to the junk heap, sooner than now if possible. Just my personal thoughts.

However, this is not about economics - its just some interesting thinking about what if.

ice

 

[SolarPro]

Best signature line I've read in a long time, Ice man. Thanks.

 

[Besoeker]

And yes, the motor-generator would be an awesome solution.

Which can be replicated using solid-state power electronics.

 

[ggunn]

Best signature line I've read in a long time, Ice man. Thanks.

It's sort of a different way of stating what my mom is fond of saying: No drop of water blames itself for the flood.