Author Topic: F&P Setup  (Read 15174 times)

0 Members and 2 Guests are viewing this topic.

dnix71

  • SuperHero Member
  • ******
  • Posts: 2513
Re: F&P Setup
« Reply #33 on: May 26, 2015, 12:21:40 PM »
In the US, UL cannot issue an approval of any plug-in grid-tie inverter. The National Electrical Code forbids that arrangement and UL is the lab that the insurers use, so they will not knowingly issue a UL cert to any device that violates the NEC.

Even if the device has proper anti-islanding features, if it plugs in, it's forbidden.

Frank S

  • Hero Member
  • *****
  • Posts: 1901
  • Country: us
  • Home with a view of Double mountain
Re: F&P Setup
« Reply #34 on: May 26, 2015, 01:36:43 PM »
There is something that I see wrong with the inverter even not used for grid tie. in the picture it shows the AC output as a 3 pin computer or electrical component input socket. No AC output on any device would ever use a cord with male contacts exposed
 I've owned several UPS units with as many as 16 AC outputs none of them ever used the recessed male socket as an output those were always reserved for input sockets. Additionally the larger UPS units and some of the smaller ones had provisions inside a removable panel for hard wiring. for the AC input and a separate panel on some for a hardwired AC output.
 My Dimensions inverter has an AC duplex output socket Plus provisions for hard wiring the AC
 If I was to buy one of the inverters that is the subject of the OP the first thing I would do is lose that recessed male AC output socket and install the proper socket if I were going to use if for anything.
 If I was thinking about the possibility of a grid tie it would have to have a terminal block inside for hard wire with a circuit breaker
 But that is just my opinion
I live so far outside of the box, when I die they will stretch my carcass over the coffin

Bruce S

  • Administrator
  • Super Hero Member Plus
  • *****
  • Posts: 5370
  • Country: us
  • USA
Re: F&P Setup
« Reply #35 on: May 26, 2015, 02:33:42 PM »
Frank S;
Man-O-Man I must be getting old! I totally missed that part; even while seeing it a wondering WTF!!

Thanks for pointing that out too!
A kind word often goes unsaid BUT never goes unheard

oztules

  • Hero Member
  • *****
  • Posts: 1477
  • Country: aq
  • Village idiot
Re: F&P Setup
« Reply #36 on: May 26, 2015, 03:26:27 PM »
Frank, it is a different animal entirely...

A UPS can output power on it's own volition, a grid tie cannot... If you look at the circuits of how it interfaces with te grid, you will see it is hard switched by the grid.. it has no way of generating the 50 or 60hz signal itself... nor can it output DC directly, as the push pull circuits control the sine wave power from the low side, and without the inout signal from the grid, cannot function anyway.

So the pins on the exposed socket can never have any output unless they are connected to the grid.... period.

All the safety ravings thus far have really been a nonsense . How a little grid tie with no ac input can cause death or destruction, trying to drive a grid is an impossibility. If the grid goes down, it will look like a dead short to any voltage source.. so thats out... maybe a generator could struggle on with huge leakage in the coils that allowed the motor to not stall would cause some residual voltage to try to drive the neighborhood on it's own.... but an output stage in a grid tie inverter that uses the grid as the driving signal.... it just does not stand up to scrutiny.

So it may be illegal over in USA but maybe not other places, it my be a silly project for other technical reasons and it may be  financially dangerous because of insurance reasons....and  any one of those is a show stopper.... but as a simple safety issue from islanding is a furphy, and does not stand up to even basic scrutiny.

It will be interesting to see how that inverter could somehow output AC when the grid goes down, and provides it with no sync  and drive signal, and a humongous short circuit of a load.... I'm  just incredulous.

Franks observations show how confusing one thing with another causes slanted truths amongst even the boffins.

To recap... the gate drives on these little units I have inspected are driven directly from the grid itself. It is not computer generated from the inverter. It is a grid slave. It cannot output any AC without the grid to switch the fets.... and Even if it had DC in the HV stage, there is no capacitive storage at all... not even 1uf of voltage storage in the HV side to even put out a stored DC shock.

It is not a ups type of thing that can generate on it's own.. it has no gate drives without the grid.... none. so cannot get through a transformer in any way even if it had some EMF somehow in the hv side.

Safety is not to be taken lightly, but crying wolf does no good either.

Upmarket fancy grid tie/back up inverters pose much more of a realistic risk of output faults, as they have drive systems that can operate independent of the grid, and a programming glitch or fault can in fact output AC without a grid, and on a small circuit, may be able to try to drive a few houses when the power drops... but these cheapy units don't have that facility.

So Frank and Bruce, it is an input socket, and once an input is established, it can "push back" against that input, and create what is effectively an output.... but not without the input in the first instance... and from then on.. it is a slave, not a master.


..... oztules
« Last Edit: May 26, 2015, 03:33:42 PM by oztules »
Flinders Island Australia

Mary B

  • Administrator
  • SuperHero Member
  • *****
  • Posts: 3169
Re: F&P Setup
« Reply #37 on: May 26, 2015, 04:22:12 PM »
If you must use small inverters go with something approved like the Enphase micro inverters.

Mary B

  • Administrator
  • SuperHero Member
  • *****
  • Posts: 3169
Re: F&P Setup
« Reply #38 on: May 26, 2015, 04:31:11 PM »
When we had the f0 tornado coupled with 95mph straight line winds across the entire southern half of MN we had line crews here from 20+ other states replacing snapped off poles. Crews who did not know the local area, crews who may not have access to information on who is using solar grid tie in the area...

Crew that worked from my town for 3 days got a treat the second day, it was my annual BBQ and we ran plates to their camp that night so they could have a warm meal. They had been surviving on MRE's... I had generator power so was able to still have everyone over plus half the neighborhood that I invited after power went down and they had no way to cook.

Do you really think that in the event of a line problem the linespeople go and manually disconnect every site that *might* backfeed incorrectly?  And then reconnect manually afterwards?

Rgds

Damon

Frank S

  • Hero Member
  • *****
  • Posts: 1901
  • Country: us
  • Home with a view of Double mountain
Re: F&P Setup
« Reply #39 on: May 26, 2015, 08:12:34 PM »
Oztules ; Thanks for the clarification on the socket in this inverter.
 I will admit that grid tie Solar without battery backup and most probably Generator back up as well makes very little sense to me. If I had grid I would want power in my home even if the entire North American grid was fried
 I was thinking that  all it would take to insure there could be no back-feed to the grid should it go down would be a NEMA or other type magnetic motor controller  rated to the appropriate size, Connected up line of the inverter (not one of these obviously)with the coil connected to the line. Should the line drop out the contacts would open with no possibility of reverse current feed to the grid.
 However in doing this it would require a circuit similar to those in a UPS to insure frequency matching to be able to reconnect to the grid.
 I am guessing that these little 1000w  solar grid tie inverters have their place for reducing the amount of electricity being paid  for through the meter 
I live so far outside of the box, when I die they will stretch my carcass over the coffin

oztules

  • Hero Member
  • *****
  • Posts: 1477
  • Country: aq
  • Village idiot
Re: F&P Setup
« Reply #40 on: May 26, 2015, 10:02:03 PM »
Yes Frank, I'm with you  there.... re isolation...

In my case it is a double pole double throw manual switch.... it is not possible to back feed the grid  this way from the big house inverter.

I have two grid tie systems in place, one is dedicated to the real grid and is approved inspected  and wired into the main panel.... upstream ( grid side) of the changeover switch.

The second grid tie panels drive into the inverters output direct, and charge the batteries through that too. It means the house does not run on the grid, unless I switch over to it.... and that isolates the home grid system entirely. The "normal" solar grid tie works with the grid all the time normally.

Auto switching between the two does not excite me at all, as I am never using the grid for the house anyway. The system is big enough to support itself in any weather, and any loads  I can find  to throw at it.... the grid is just a free emergency back up... opposite to what most folks do.

I'd dump the grid entirely... except it is revenue positive, and so cheaper than a back up generator....



.........oztules
Flinders Island Australia

Bruce S

  • Administrator
  • Super Hero Member Plus
  • *****
  • Posts: 5370
  • Country: us
  • USA
Re: F&P Setup
« Reply #41 on: May 27, 2015, 11:57:02 AM »
OZ;
My stance remains for safety.
Your knowledge of electronics is light years ahead of mine.

 I don't like being part of the wolf pack either, but,,, the units you have been able to inspect, if you have pics , I'd certainly like to compare those versus the ones available to us.

Of the different sizes I've had the luck of seeing inspections and installs for , only one was done the correct way.
AND you are very correct, it cannot be the fault of the unit if the installers do not do it right the first time, no matter if it's a cheap unit or a high dollar one. BUT the insurers are the quickest ones to jump ship !!

I have the good fortunate to work with FIU, they are the ones that go to a fire and determine was caused the fire and then report them to the insurance agencies.

Once I get the clearances I'll post the building that this occurred in and what it looks like now, but American lawyers being the way they are  >:( , I could be of retirement age before then!!
 
The fires aren't caused by the grid going down, they are caused by these units failing inside or low quality QA inspections.


This might look familar :(.
 
It is very unfortunate , cause the poor guys were sure they had done everything correctly.

OF all things, the one place the I was quietly fighting with MWS has actually put out a nice video of how to connect it correctly.

https://www.youtube.com/watch?v=S93wbGlzsJg
I'm not one to give out free advertisement, however, for those located here in the USA and are  thinking of using these units,,, PLEASE watch the posted video.

AND pay attention to the part about NOT over driving the unit.

I do not grid tie, my poky little 100w system is way to small for that. 

The unit that was installed the correct way,, is for solar only and even I pulled the AC plug and measured it just like the guy in the video, I lost a 3-drink bet on that one.

Cheers
Bruce S
A kind word often goes unsaid BUT never goes unheard

oztules

  • Hero Member
  • *****
  • Posts: 1477
  • Country: aq
  • Village idiot
Re: F&P Setup
« Reply #42 on: May 27, 2015, 05:40:17 PM »
Safety is fine to worry about Bruce, but needs to be for the right reasons.

These little units will fail fairly early on due to cap failure. They are subjected to unrealistic ripple, with the barest amount of capacity and bulk... consequently, the first part to blow will probably be on the low side pwm fets, that then possibly spreads to a problem on the hv side... and the usual black smoke.

They are not suitable nor will they ever be suitable to be connected to the grid over here, as they do not follow the AS3777 code for grid connect inverters.

Being a slave  to the grid waveform, means they cannot chose to disconnect or chose to connect... they connect and thats it. The grid drives the fets as I mentioned before.

This brings a new set of problems that can't be solved with that topology... from an islanding safety aspect, it is probably practically fine...... no grid, no run possible..... but from a regulations aspect, totally unrealistic.

The regs require that the unit WILL wait for a set period of clean power before it can begin to backfeed. Initially this is quite fast for the first connect for the day... any interruption from then on will require a mandatory set time ( minutes not seconds ) of monitoring for "clean" grid power before it can reconnect... any freq  or voltage infraction in that time will necessitate a new count down... so a noisy grid will see very little connect time......

Here we have windmills and a small power station, so the freq is unstable some days, and will vary by plus or minus 1 hz  The inverters are only allowed to see a half hertz movement before disconnect and wait all over again... so on a windy gusty day, you may get 1-3kwh into the grid, and on a still day 24-27kwh

The cheapies will follow the frequency very differently...... the output is hard switched by the mains, so the sampling done on the LV side is all that can turn it off... it cannot turn off the gate drive signals on the output fets as they are supplied gate drive from  the grid, so all it can do is stop the step up voltage from occurring... ie the low side pwm that would normally supply the sine wave  power to the fets to switch...... can be switched off.... but isolation cannot be achieved ( no relays either)... and we have no idea of what the programming is, but the fact they connect immediately gives us an idea that they do not follow the rules at all.

So it tuns out that it is not an actual safety via electrocution problem, it is a perceived safety via regulations that is at issue.... ( that and the fact that these things will likely not see a year out before the caps fail, and bing the thing to a grubby end)

House wiring , fusing and what the thing is mounted on and where will determine the fire hazard it will present..... we know it will fail... and probably spectacularly at some point, ... so it is the installation and position that will determine how that demise may spread it's pain that is far more important.... and that can be managed too, but the failure to be able to follow the AS3777 regs is terminal really.

Added together, it is very unlikely that if the thing is earthed that it can present a credible  electrocution danger or islanding danger... basically the same as an induction motor over running as a grid tie device ( micro hydro setups?).... so then it needs to be seen as a fire hazard, and that is manageable too... but the regs make it a no no... thats the real show stopper on all of this.

If they were to program the low side to follow the AS3777 regs, and had a credible isolation relay...  then theoretically is could be passed I suppose... which I guess the one Mary alluded to must do.

If your willing to ignore them at your peril, then ........ ....

But we need to keep in mind facts, and know why we are anti this or anti that... safety is a motherhood thing, like the environment with cuddly creatures appeals to the populace.... but we need to understand why we are anti whatever.... hiding behind safety or fire is too easy... we need to get back to basics and know why and what.....  or we end up with the governments we deserve... and look at what that has gotten us...


...............oztules
Flinders Island Australia

bart

  • Full Member
  • ***
  • Posts: 200
  • Country: us
Re: F&P Setup
« Reply #43 on: May 27, 2015, 05:50:42 PM »
About the video.
  I'm pretty sure those disconnects don't have a DC rating. Yes, you could use one, but....
MWS has started radio advertising in Springfield.

dnix71

  • SuperHero Member
  • ******
  • Posts: 2513
Re: F&P Setup
« Reply #44 on: May 27, 2015, 07:22:59 PM »
What is the practical effect of backfeeding the grid from a branch circuit, assuming the branch circuit is capable of handling the current? These are not plugged into the point of service, just whatever outlet happens to be handy. To push back requires a voltage higher than incoming. Would you get much benefit from that or would your appliances simply see a higher voltage when running and use more power and burn out faster.

joestue

  • Hero Member
  • *****
  • Posts: 1759
  • Country: 00
Re: F&P Setup
« Reply #45 on: May 27, 2015, 08:18:12 PM »
Would you get much benefit from that or would your appliances simply see a higher voltage when running and use more power and burn out faster.

far as i know the nec limits are 5% voltage drop.

if my numbers are right you need 133 feet of 14 awg wire to get 5 volts drop at 15 amps. so, in practice you should not see a 4% drop in voltage ever.
My wife says I'm not just a different colored rubik's cube, i am a rubik's knot in a cage.

DamonHD

  • Administrator
  • Super Hero Member Plus
  • *****
  • Posts: 4125
  • Country: gb
    • Earth Notes
Re: F&P Setup
« Reply #46 on: May 28, 2015, 07:24:47 AM »
@oztules

Just FYI, and hoping that I have my facts right, here in the UK for grid tie (G83 and G59) the inverters do have to drop off at about 50.5Hz on the high side, but I believe that they are meant to hold on like grim death all the way down to 47Hz.

The last significant nationwide event we had here involved a big nuke tripping off unexpectedly, then separately a big coal plant, and THEN a bunch of smaller gen plant that should have stayed on below 49.5Hz to help ride out the glitch tripped out prematurely and 500,000 people had to be 'load shed'...

Rgds

Damon


From: http://www.earth.org.uk/note-on-dynamic-demand-value.html

Quote
An analysis of figures supplied by National Grid for 2008/05/27 (.xls) where a series of generator problems resulted in 500,000 people being 'load shed', ie getting a 40-minute power cut, suggests that over ten minutes were spent outside normal operational limits, and about nine of those outside statutory limits, with ~5% at or below -0.1Hz (ie frequency ≤49.9Hz) and ~21% at or below -0.05Hz (ie frequency ≤49.95Hz). For a large chunk of the day various DNOs (regional distributors) were helping curb demand by reducing voltage too.
« Last Edit: May 28, 2015, 10:34:29 AM by DamonHD »
Podcast: https://www.earth.org.uk/SECTION_podcast.html

@DamonHD@mastodon.social

dnix71

  • SuperHero Member
  • ******
  • Posts: 2513
Re: F&P Setup
« Reply #47 on: May 28, 2015, 10:07:36 AM »
joestue I was thinking about the US split phase 240 being an issue. If you grid-tie a home here through a commercial vendor, they backfeed 240 at the panel. The service for the home is split, though. The transformer on the pole is center-tapped neutral/grounded. Each side from center is 120. Inside the house neutrals are typically shared, even though that isn't good practice.

So, if you backfeed 120v from a branch, you are loading back to the pole transformer assymetrically and inside the house the neutrals have stray voltages from appliances and there is an indirect connection between the two halves of 120 through shared neutrals and appliances that use both 240 and 120 like your stove. The stove burners run on 240 but the light inside is 120.

Backfeeding inside 120 seems like a bad idea, period. Backfeeding inside 240 with no neutral doesn't seem so bad.

Bruce S

  • Administrator
  • Super Hero Member Plus
  • *****
  • Posts: 5370
  • Country: us
  • USA
Re: F&P Setup
« Reply #48 on: May 28, 2015, 10:58:34 AM »
OZ;
First and Foremost, thanks for the very informative post!!
I think I'm going back to being a doorman  :o.

@bart;
Good eye!!
I'm told they do actually have a DC rating, but they haven't answered "what" the DC rating on that disconnect is. DE-rating an AC disconnect is something even I do, but who in their right mind will put their hands inside to disconnect ?
I tried to find a better video to put up, alas, GreenPowerscience's is even worse :(. and they go down hill from there!



A kind word often goes unsaid BUT never goes unheard

joestue

  • Hero Member
  • *****
  • Posts: 1759
  • Country: 00
Re: F&P Setup
« Reply #49 on: May 28, 2015, 12:19:15 PM »
dnx71, its drops in the bucket if the voltage rise from backfeeding the grid is less than 1% (which it should be, at the breaker box)
My wife says I'm not just a different colored rubik's cube, i am a rubik's knot in a cage.

oztules

  • Hero Member
  • *****
  • Posts: 1477
  • Country: aq
  • Village idiot
Re: F&P Setup
« Reply #50 on: May 28, 2015, 03:45:08 PM »
Damon...
" The limits on the 50Hz-nominal UK grid frequency are:

    Operational +/- 0.2Hz
    Statutory +/- 0.5Hz (1%)
    Maximum drop from an Infrequent Infeed Loss Risk (1320MW) is -0.8Hz

Also, your author states
"There will naturally be some 'wiggle' in the frequency as demand and supply will never balance exactly to the Watt at every instant, but if the wobble gets too big then something is going wrong and needs fixing. "

and the getting towards the "too big" is apparently seen by the regulators as 1% deviation.. after that they will want to take control of the loads, and by over 2% they panic and load shed.......

"

I am told by the generator folks here that they have a 1hz window ie 49-51hz to stay inside their limits legally. Diesel generators don't have a huge inertia to play with, and hysteresis problems with sharp large load variations.... like  250000w windmill attached to a 1mw diesel station.....If it was nuke or coal it would probably be the same as the UK at .5hz

I would be truly staggered if your micro generators were allowed to follow a drift in freq for more than 6 times what the statutory range for real  grid operators could, and a 6% variance  to the low side would be ...... well might as well use the cheapie chinese ones to start with.... thats looking for a free for all ungainly grid with no standards really.... and does bring to light a problem with islanding in areas with lots of micro generation... taking over the grid to some extent.... they may even be able to create a local grid.... feeding each others inputs, and gyrating around the 50hz region... and not turning off..... I would be disturbed.

If you look at your frequency distribution in that article, it is very tight, almost never going near 1% deviation ( .5hz), so tight rules around islanding are sensible, and realistic for a good clean power system... 6% low side variance would be very sloppy I think.

On still days, the frequency drifts here by .1hz, and very little more... windy days it gets to the 1hz limits... frequently.... and exacerbated by the grid ties dropping off all together at 49.5hz.... never have I seen it below 48.9.... and thats a dirt ball diesel plant with a comparatively huge mill trying to destabilize it.


......oztules
« Last Edit: May 28, 2015, 03:51:58 PM by oztules »
Flinders Island Australia

DamonHD

  • Administrator
  • Super Hero Member Plus
  • *****
  • Posts: 4125
  • Country: gb
    • Earth Notes
Re: F&P Setup
« Reply #51 on: May 28, 2015, 04:04:34 PM »
Just picked a random G59/3 form from the Web:

http://www.westernpower.co.uk/docs/connections/Generation/G59-3-Generating-Plant-Protection-Commissioning-Fo.aspx

Look at the asymmetry in the frequency tests there.

Rgds

Damon

PS. The earth.org.uk site is mine, BTW, I wasn't trying to claim it as an authority!
Podcast: https://www.earth.org.uk/SECTION_podcast.html

@DamonHD@mastodon.social

DamonHD

  • Administrator
  • Super Hero Member Plus
  • *****
  • Posts: 4125
  • Country: gb
    • Earth Notes
Re: F&P Setup
« Reply #52 on: May 28, 2015, 04:09:29 PM »
Just found this, see section 9.3.2:

http://www.amps.org.uk/static/assets/downloads/DraftG5931_170914updatev1280115trackchangev4.pdf?attach

Quote
b. 47.5Hz – 51.5Hz  Disconnection by overfrequency or underfrequency protection is not permitted in this range.

So, yes, it is highly asymmetric, with microgeneration having to stay on-line in the range 47.5 to 51.5Hz to help the grid ride out such events as major sudden loss of generation.  Remarkable!

Rgds

Damon
Podcast: https://www.earth.org.uk/SECTION_podcast.html

@DamonHD@mastodon.social

oztules

  • Hero Member
  • *****
  • Posts: 1477
  • Country: aq
  • Village idiot
Re: F&P Setup
« Reply #53 on: May 28, 2015, 06:01:05 PM »
No Damon... I think the testing and accuracy tests are wildy erratic.... but the only test that counts is the loss of mains  (LOM) test on page 6... your last link.
Can't cut and paste the pdf very well at all, so here is the start of the LOM test figures... low and behold, 49.5 to 50.5 This is the islanding test, the rest just test the accuracy and range of the units calibration systems I think.... thats why they are using outlandish figures.

-
Mains (LOM) Protection Tests
-
RoCoF
Calibration and Accuracy Tests
Ramp in range 49.5 -50.5Hz

Thats the test frequency test for shut down.... not calibration.


If your grid ran from 180v to 273v and 47 to 51.5hz .... why bother to calibrate at all.... anything goes... like a national phone system using tin cans and a piece of wet string. If your grid has come to that.... forget it.... and move to Botswana    they probably do much better than that when it actually runs.

Luckily the real figures for your grid system are very very good, and rarely move beyond .5% .......from your first paper.



...............oztules

.......oztules
« Last Edit: May 28, 2015, 06:09:09 PM by oztules »
Flinders Island Australia

bart

  • Full Member
  • ***
  • Posts: 200
  • Country: us
Re: F&P Setup
« Reply #54 on: May 28, 2015, 06:14:35 PM »
OZ;
First and Foremost, thanks for the very informative post!!
I think I'm going back to being a doorman  :o.

@bart;
Good eye!!
I'm told they do actually have a DC rating, but they haven't answered "what" the DC rating on that disconnect is. DE-rating an AC disconnect is something even I do, but who in their right mind will put their hands inside to disconnect ?
I tried to find a better video to put up, alas, GreenPowerscience's is even worse :(. and they go down hill from there!

  I save all the switches, disconnects and breakers off of scrapped out HVAC equipment that have a DC rating on the label. And there is not much that does. Have one of those similar disconnects on my condenser and it has no DC rating.

Ungrounded Lightning Rod

  • SuperHero Member
  • ******
  • Posts: 2865
Re: F&P Setup
« Reply #55 on: July 21, 2015, 03:14:50 AM »
Thanks for the tip guys.  So when I hook up the caps in series I take the line from the turbine and hook it to the the positive terminal of the 1st cap, then I put a jumper between the negative on the 1st cap and positive of the 2nd cap, then the negative of the 2nd cap would be my output.  Is that correct ?

Thanks
George

No:

Hook the F+P lead to + on the first cap.
Hook the - of the first cap to the - of the second cap.
Take your output from the + of the second cap.

Alternatively, tie the +es together, one - to the F&P, the other - to the output.

The point is that the caps are in series and facing opposite directions.

A slight leakage current in the caps causes the "floating" tied point to run up in voltage until each cap is cycling between being discharged and being charged in the forward direction, rather than being charged forward, then being charged backward.  (Backward voltage on an electrolytic cap, over time, causes an electrochemical reaction that breaks down, rather than builds up, the insulation between the plate and the electrolyte.  After a very short while - like seconds or a minute or so - the cap shorts out.)