50Hz 230 volt power in a 60Hz world

Status
Not open for further replies.

tallgirl

Senior Member
Location
Great White North
Occupation
Controls Systems firmware engineer
I figure y'all are the right people to ask. Not that you've ever been asked this before, but because I'm sure this will be an interesting discussion.

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?
 
Last edited:

hillbilly1

Senior Member
Location
North Georgia mountains
Occupation
Owner/electrical contractor
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.
 

Besoeker

Senior Member
Location
UK
I figure y'all are the right people to ask. Not that you've ever been asked this before, but because I'm sure this will be an interesting discussion.

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?

I don't know about your code issues but it wouldn't be very difficult to rectify it and put it back into the supply via a mains-commutated inverter.
It's something we routinely do with some of our larger drive systems.
 

BillK-AZ

Senior Member
Location
Mesa Arizona
Years ago when testing battery capacity we solved this problem with a stacked pair of Trace (now part of Schneider Electric after being Xantrex) SW4024 inverters that were programmed to sell when the battery voltage was above a specified value. We used a simple DC/DC down converter from the nominal 48-volt battery, set up for constant current out of the test battery. Worked fine.
 

SolarPro

Senior Member
Location
Austin, TX
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.

Hey, at least it's offsetting your heating loads for the time being.

The rub comes in the summer, when you're paying to generate the heat, and to eliminate it!
 

tallgirl

Senior Member
Location
Great White North
Occupation
Controls Systems firmware engineer
Years ago when testing battery capacity we solved this problem with a stacked pair of Trace (now part of Schneider Electric after being Xantrex) SW4024 inverters that were programmed to sell when the battery voltage was above a specified value. We used a simple DC/DC down converter from the nominal 48-volt battery, set up for constant current out of the test battery. Worked fine.

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.

I'm not completely privy to all the decisions, but my understanding is that the batteries were the deal-breaker. I have a 520Ah bank for my system, and I'm comfortable with that, but we have a growing array of 50Hz microinverter panels (these are ACPV panels, not stand-alone inverters and DCPV panels) and that can get to be a lot of power to control. I'm comfortable telling my company's clients how to set up the control equipment, but those are for systems that are "production", rather than "test" or "development".

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. What I'm curious about is any Code restrictions or requirements for taking that 50Hz power and using it for productive use, because Summer isn't all that far off.
 

tallgirl

Senior Member
Location
Great White North
Occupation
Controls Systems firmware engineer
Hey, at least it's offsetting your heating loads for the time being.

The rub comes in the summer, when you're paying to generate the heat, and to eliminate it!

We had some of that through the Fall. The 50Hz power supply is in the electrical closet, just outside the bullpen where the software team sits. It was definitely affecting the thermostat in our area!

I'd love to be able to talk more about what's going on, because I'm having the time of my life doing what I'm doing, but there are secrets that can't be discussed.
 

hurk27

Senior Member
I totally confused as to why one would want to install a PV system with inverters set for 50hz in a 60hz world (the US) it would seem to me to to have the least amount of conversion (for less losses) to be able to sell the power back to the utility at peak times and convert via additional inverters for the loads needed to run a 50hz then to try to re-convert the 50hz to 60hz to sell back to the utility.

A switching system to switch the two different hz inverter systems in and out of the DC buss would seem to be the most effective system to me?

But then again pardon my ignorance as I'm not really into the PV world as I use inverters for a different means.
 

tallgirl

Senior Member
Location
Great White North
Occupation
Controls Systems firmware engineer
Wayne,

It's for product development. We have a 60Hz product and want to manufacture a product for parts of the world that use 50Hz.

That's one of the things that's most interesting about PV -- all the different systems in use out there. For example, Mexico is mostly 127/240 Wye, as I understand it. Any country that's small (and doesn't get along with its neighbors ...) or is an island has unstable voltage and frequency.

Your suggestion that the power be converted on a DC bus is what I'd suggested -- some vendors inverters can be AC coupled (one inverter backfeeding the output of another) and that can be used for frequency or voltage conversion. Stick batteries in the middle and DC output of one AC coupled inverter can be DC coupled to another with a completely different frequency system.
 

hurk27

Senior Member
Wayne,

It's for product development. We have a 60Hz product and want to manufacture a product for parts of the world that use 50Hz.

That's one of the things that's most interesting about PV -- all the different systems in use out there. For example, Mexico is mostly 127/240 Wye, as I understand it. Any country that's small (and doesn't get along with its neighbors ...) or is an island has unstable voltage and frequency.

Your suggestion that the power be converted on a DC bus is what I'd suggested -- some vendors inverters can be AC coupled (one inverter backfeeding the output of another) and that can be used for frequency or voltage conversion. Stick batteries in the middle and DC output of one AC coupled inverter can be DC coupled to another with a completely different frequency system.

Actually it's 127/220 volt wye 240 volt line to line on a wye would produce a 138.6 volt neutral voltage as found on some generator configurations.

I'm a little confused? are you saying that you can feed from one inverter into another inverter then DC coupled to another to get a different frequency? how does a inverter that is outputing AC output DC?

The way I was thinking is that the PV cells produce DC, this then charges batteries that become the DC buss, from this DC buss we take DC power to feed inverters at which frequency we need such as 50hz.

At work we have trains and cranes that run on 250 volt DC, we have inverters that take this 250 volts DC and change it to 120/240 volts AC 60hz for different electronics that are used on them.

I wonder if any inverter manufacture could design an inverter that could be switched between 50hz and 60hz and the output voltage readjusted for different voltages, kind of a one size fits all inverter? I could not see it being hard to do as the voltage output is adjustable on most inverters and the frequency is fairly easy to change depending upon the design of the oscillator circuit?

As far as the unstable voltages and frequency on these remote parts of the world, you already have one of the things that will stabilize them and thats DC, convert the incomming power to DC to charge the batteries, then create a DC buss then design a PV system to recharge this DC buss then re create the AC through the inverters, Dual conversion UPS systems already do this as does VFD drives, the problem is going to be able to design a inverter that can stay in sync with the incomming supply to always be putting kws back into the grid if the frequancy is not stable, it would require a frequency regulation system that can respond fast enough to keep the inverters output always leading the grids frequency with regulation that also monitors the amount of current it is trying to upload.

The problem with the above is going to be that when the grid frequency varies so will your inverters output so the only way around this would be to use two inverter systems and let a main inverter take care of the main loads then use a special inverter to take care of the back feeding into the grid this way the two are isolated like any dual conversion UPS, no matter which way you look at it, the inverter tied to the grid will always have to follow the frequancy of the grid.

We are not used to dealing with this type of problem as we are so very acustom to having a stable grid but I can envision the problems when we don't have it, and some examples are UPS systems running off generators that have speed regulation problems that can cause the UPS to trip out on out of sync issues.

With our stable grid when we load our service down it only cause a voltage drop problem but if we are running on a generator it causes the engine to slow down causing the frequency to change at least till it speeds back up to catch up to the load so a test using a generator can be good to test whether a inverter can follow the changes in frequency when it is loaded if you can get a inverter designed to follow the frequancy and keep it leading the supply frequancy.
 

kwired

Electron manager
Location
NE Nebraska
I wonder if any inverter manufacture could design an inverter that could be switched between 50hz and 60hz and the output voltage readjusted for different voltages, kind of a one size fits all inverter? I could not see it being hard to do as the voltage output is adjustable on most inverters and the frequency is fairly easy to change depending upon the design of the oscillator circuit?

Can it be done? I think so, don't VFD's already do this?

Is there much demand to do it for standardized products vs custom made products is likely the question.
 

tallgirl

Senior Member
Location
Great White North
Occupation
Controls Systems firmware engineer
Wayne,

Thanks for the correction -- I got 240 stuck in my head eons ago and no one has corrected me since.

DC coupling refers to connecting two different inverters via a DC bus, typically with batteries on the bus as well to provide a stable DC supply. It can also refer to using an unstable generator (like a cheap gasoline powered one) to drive a plug-in battery charger. Iota, for example, makes a number of 12, 24 and 48 volt chargers that can operate off 120 volts at 15 amps or less. Rather than feeding a cheap generator to the AC inputs of an inverter, using an Iota to charge the batteries will allow a much smaller and cheaper generator to be used.

There are inverters that have some amount of selectivity with the output voltage. I don't know about changing frequency without changing some of the electronic components. I'd expect the magnetics would have to be changed, at a minimum. As for 250 volt DC, can't help you there. Sorry :(
 

Besoeker

Senior Member
Location
UK
Can it be done? I think so, don't VFD's already do this?

Is there much demand to do it for standardized products vs custom made products is likely the question.
A variable frequency inverter with an active front end can do that and they are a relatively standard bit of kit. Feed it with 50Hz at the load side and get 60Hz out on the line side.
Even simpler would be a mains-commutated inverter.
 

tallgirl

Senior Member
Location
Great White North
Occupation
Controls Systems firmware engineer
A variable frequency inverter with an active front end can do that and they are a relatively standard bit of kit. Feed it with 50Hz at the load side and get 60Hz out on the line side.
Even simpler would be a mains-commutated inverter.

Vendor and part numbers?
 

Besoeker

Senior Member
Location
UK
Vendor and part numbers?

Almost all of the major drive manufacturers.
ABB, Siemens, AB, Vacon, to name but a few.

I can probably provide you model types and part numbers if you give some fairly basic information.
Which way do you want to go? Mains-commutated or active front end?
Are harmonics an issue for you?
Single phase or three phase?
What voltage do you want out?
Is 5kW the rating of your system?
Do you need electrical isolation between input and output?
 

tallgirl

Senior Member
Location
Great White North
Occupation
Controls Systems firmware engineer
Almost all of the major drive manufacturers.
ABB, Siemens, AB, Vacon, to name but a few.

I can probably provide you model types and part numbers if you give some fairly basic information.
Which way do you want to go? Mains-commutated or active front end?
Are harmonics an issue for you?
Single phase or three phase?
What voltage do you want out?
Is 5kW the rating of your system?
Do you need electrical isolation between input and output?

The output from a VFD, or anything that remotely smells like a VFD and isn't UL 1741 and/or IEEE 1547 compliant, won't work and wouldn't be code-compliant.

VFDs don't change the frequency -- most work by using PWM to fake a different frequency. It's good enough for a motor, but lousy for a PV inverter. It's even worse to be back-feeding to an electric grid.
 

Besoeker

Senior Member
Location
UK
The output from a VFD, or anything that remotely smells like a VFD and isn't UL 1741 and/or IEEE 1547 compliant, won't work and wouldn't be code-compliant.
I did tell you that I can't comment on code requirements


VFDs don't change the frequency
So what do you think Variable Frequency Drive actually means?

It's good enough for a motor,
Yes, to feed a motor. But run from output to input does not depend on motor characteristics.

It's even worse to be back-feeding to an electric grid.
HVDC stuffs oodles of the stuff back into the grid. How bad is that??

And yes, not only will work. It does.
 

hillbilly1

Senior Member
Location
North Georgia mountains
Occupation
Owner/electrical contractor
Your original post lead us to believe you wanted to recoup wasted energy, and there has been many suggestions doing that, but apparently none of them works for you, sounds like the air in Texas will stay a little warmer!
 
Status
Not open for further replies.
Top