navitron
 
Renewable Energy and Sustainability Forum
Welcome, Guest. Please login or register.

Login with username, password and session length
News: Anyone wishing to register as a new member on the forum is strongly recommended to use a "proper" email address - following recent spam/hack attempts on the forum, all security is set to "high", and "disposable" email addresses like Gmail, Yahoo and Hotmail tend to be viewed with suspicion, and the application rejected if there is any doubt whatsoever
 
Recent Articles: Navitron Partners With Solax to Help Create A More Sustainable Future | Navitron Calls for Increased Carbon Footprint Reduction In Light of Earth Overshoot Day | A plea from The David School - Issue 18
   Home   Help Search Login Register  
Pages: [1] 2   Go Down
  Print  
Author Topic: Exploding inverters  (Read 1019 times)
floydy
Newbie
*
Offline Offline

Posts: 6


« on: May 16, 2019, 09:05:46 PM »

Hello,
I've been lurking on here for a few years- here's my first actual post and a tale of woe to boot!

Recently I took on what seemed a straightforward job to replace  an inverter on a Proven 6Kw machine for a friend. It was on it's original WB6000 it only has a Vac-Bfr error and some sort of firmware problem, but I've not managed to repair it yet.

I opted to replace it with an Aurora 3.6 and an SMA SB3000 (reconfigured to wind) paralleled up. The thinking being that the early SMA inverters are of transformer type and DC/AC sides are isolated. In my mind the Aurora would superimpose AC onto both legs of the DC feed from the turbine rectifier but that would have no effect on the windy boy, it would happily float around on the DC side.

The system had been running for a few weeks on just the Aurora (with a power one wind protection box) while I configured the SMA. When the SMA was added in parallel a large bang ensued at the moment of grid connection.... Aurora varistor popped (and maybe more), grid breaker tripped.

 It looks as though the SMA is not as isolated between the two sides as I thought! I can't make sense of this though. As part of my testing, I ran the SMA off rectified mains with the AC out connected back to the same feed. It was absolutely fine, which confirmed my thoughts on it's suitability.

So, what have I missed here?!

Cheers,

Andy
Logged
Tinbum
Hero Member
*****
Offline Offline

Posts: 1164


« Reply #1 on: May 16, 2019, 10:02:46 PM »

In my mind the Aurora would superimpose AC onto both legs of the DC feed from the turbine rectifier but that would have no effect on the windy boy, it would happily float around on the DC side.


I don't understand. Your trying to feed ac and dc into the DC input of the SB3000?  Huh
?
Logged

85no 58mm solar thermal tubes, 28.5Kw PV, 3 x Sunny Backup 5048, 3x Sunny Island 5048, 2795 Ah (135kWh) (c20) Rolls batteries 48v, Atmos wood gasification boiler, Brosley wood burner, 2000lt buffer tank and 250lt DHW
rogeriko
Hero Member
*****
Offline Offline

Posts: 1387



WWW
« Reply #2 on: May 16, 2019, 10:09:22 PM »

You cant parrallel inverters like that. What happens when one shuts down for some reason, then the other one has to take all the load. I doubt protection boxes react that quickly. You need isolation transformers etc to make it work and you will loose half your power due to inefficiencies.
Logged

floydy
Newbie
*
Offline Offline

Posts: 6


« Reply #3 on: May 16, 2019, 10:52:39 PM »

Tinburn - Re feeding AC and DC into SMA - no! Both + and - should should have an identical AC component. This is only a problem if it's referenced to ground, which I don't think it is. The DC inputs to SMA are floating as far as I know. They are isolated from the mains and from ground Or at least I thought they were.

Rogeriko - It's quite acceptable to parallel inverters up. I have an installation I look after with 3 WB 3800s per grid phase paralleled up on the rectified DC input from turbine - no isloation transformers there. Also if paralleling Auroras, only n-1 of the inverters need an isolation transformer, so a 3 phase install would only have them on 2 phases.

Proven themselves used to use 2 WB 3000s on these installations.

I'm just trying to work out what is different with a Windy boy with it's inbuilt isolation transformer and say a 2nd Aurora with an isolation transformer on the grid side!

Thanks for the thoughts so far...
« Last Edit: May 16, 2019, 11:20:59 PM by floydy » Logged
Iain
Hero Member
*****
Offline Offline

Posts: 1708


« Reply #4 on: May 17, 2019, 06:49:01 AM »

Hi
I would have thought that if two inverters can run in parallel they would have to have identical load curves in order for them to share the load.
So I would again imagine that 2, same make, identical curve inverters might work. (Similar to 2 generators running in parallel.)
I did hear that if 2 Auroras had to run itogether the outputs would have to be isolated from each other via transformers.

I think due to the different designs of the 2 inverters you would have a lot more problems even if it were possible on paper.
If it has been done with 2 windyboys in the past, I think that would be the way to go.
It is very difficult to isolate components on a common DC input especially running 2 different make inverters.

Iain
Logged

1.98kWp PV (11 x Sharp 180 and SB 2.5)
20 x 65mm Thermal and 180ltr unvented
Powervault 4Kw - G200 Lithium-Ion (LiFePO4)
9000ltr rainwater storage   Plymouth
marshman
Hero Member
*****
Offline Offline

Posts: 914


WWW
« Reply #5 on: May 17, 2019, 09:25:28 AM »

I haven't got an answer but when I had my 1kW Futurenergy turbine running the standard setup was to use 2 Soladin  Windmaster 500 inverters. I ran mine like that for around 5 years. They absolutely did not have identical load curves. I deliberately set one to cut in before the other. The reason was that at very low windspeeds when they both cut in together they would virtually stall the turbine, so I staggered the cut in points to make the transition more progressive.

I can't recall if these were transformer isolated or not but they were just paralleled up on both the input and output side.

Roger
Logged

3.15kWpk (15xSharp ND210)/SB3000. & 3.675kWpk (15 x Suntech 245WD)/SB4000TL, 10kW GSHP driving Wirsbo underfloor heating from 1200m ground loops. 10' x 7' solar wall (experimental). Clearview 650 Wood Burning Stove. MHRV - diy retrofit. Triple glazing.
floydy
Newbie
*
Offline Offline

Posts: 6


« Reply #6 on: May 17, 2019, 09:53:23 AM »

I've found in practice that the two inverters don't need matching curves too - it's the sum of both curves that is important. It's OK to have one inverter do more work than the other at certain wind speeds.


Logged
Nickel2
Hero Member
*****
Offline Offline

Posts: 1686


Method mixed with Madness


« Reply #7 on: May 17, 2019, 10:32:07 AM »

From a logical point of view, I see it this way: Inverter no.1 sees mains voltage, then sets it's own output level marginally above that, in order to push current into the grid. Connect inverter no.2 to the grid, it sees the voltage at the point where inverter no.1 is connected, and increases it's nominal output voltage marginally to try and push current into the grid. Inverter no.1 sees the local voltage rise and ups it's game. The two then compete until failure. If there is a long enough cable between the (low-impedance) grid and the variable source, local voltage may exceed the operating voltage of one inverter, causing it to shut down. The other inverter will then be left trying to stuff a load of current into the grid, that it cannot supply, with possible failure as a result.
A pair of inverters from the same company will have software interconnection to keep them in sync, and share the load. Unless each inverter knows what the other is doing and co-operates, there will be a fight, sometimes to the death... 
Logged

1.140kW mono south-facing at 49*
EpEver 4210A at 24v
24V 400 Ah battery. (4x200Ah FLA)
EpEver STI1000-24-230 pure sine inverter
Of course it'll work. (It hasn't caught fire yet).
biff
Global Moderator
Hero Member
*****
Offline Offline

Posts: 11878


An unpaid Navitron volunteer who lives off-grid.


« Reply #8 on: May 17, 2019, 11:18:57 AM »

Dabbling about in AC
                  Is not for the faint hearted and should never be undertaken without the proper instructions and wiring diagram. I speak to the members who are reading this thread. Even off grid efforts to twin identical UPSSs with the widow maker Y cable always ends with a bang and profanities.
  And yet this was something  that I really wanted to get to grips with. The idea being that one low powered inverter would run the house on any load up to 1kw . Then if I wanted to run the washing machine or anything more powerful I could switch on another identical inverter.. The only machine that I could find that could do this was the Symmetra RM. This UPS has 4 x 1.4kw modules and it is a life critical UPS.  It is a 120 vdc and is connected to 2 ton of  120 volt lead acid . It is the bees knees in UPSS and can do all kinds of circus tricks like swapping round power modules while under load. Even though it is double conversion it is still very heavy..
   I recall that Doug in the states built one of the first proper ground mounts and  each panel had its own little mini inverter. (I think)  they all met up at a central point at the array and fed the house in full grid voltage AC.
  That was all new to me back then. (10 years ago ?)
 Yet we all know that somewhere in these box's of tricks is a big transformer which eats the juice.
  Some things are better done by the book. 
         Biff
Logged

An unpaid Navitron volunteer,who has been living off-grid,powered by wind and solar,each year better than the last one.
Westie
Hero Member
*****
Offline Offline

Posts: 557


« Reply #9 on: May 17, 2019, 11:24:13 AM »

From a logical point of view, I see it this way: Inverter no.1 sees mains voltage, then sets it's own output level marginally above that, in order to push current into the grid. Connect inverter no.2 to the grid, it sees the voltage at the point where inverter no.1 is connected, and increases it's nominal output voltage marginally to try and push current into the grid. Inverter no.1 sees the local voltage rise and ups it's game. The two then compete until failure. If there is a long enough cable between the (low-impedance) grid and the variable source, local voltage may exceed the operating voltage of one inverter, causing it to shut down. The other inverter will then be left trying to stuff a load of current into the grid, that it cannot supply, with possible failure as a result.
A pair of inverters from the same company will have software interconnection to keep them in sync, and share the load. Unless each inverter knows what the other is doing and co-operates, there will be a fight, sometimes to the death...  

I don't think having multple GTIs connected is a problem so long as each GTI has is own generator, many of us have two GTIs at home with separate generators, many of us have modular systems where there may be 16 micro GTI's... ie. one per panel. So paralleled on AC side is fine, the big question mark  is over sharing the generator between two GTIs, I'm no expert on wind but on a PV system this would surely cause a problem for MPPT trackers as the each inverters tracker will be fighting with the others to find the sweet spot?
« Last Edit: May 17, 2019, 11:27:14 AM by Westie » Logged

4kwp south facing array  SMA 4000TL grid connected.  2x30tube Navitron solar thermal panels (east/west). Arada 5kw S/C WBS. 25000Ltr underground rain water tank. KTM E-Bike  Cool
floydy
Newbie
*
Offline Offline

Posts: 6


« Reply #10 on: May 17, 2019, 04:53:21 PM »

A quick update. The fault is actually a result of mechanical damage from the courier... A little background here - this was a job for a friend a few hundred miles away, when I was last down there I set up the Aurora and left connectors ready to plug into the windy boy, which I posted down after configuring it back at my place.

Now it's had an internal examination, the inverter has clearly been dropped on the way down, causing several of the IGBT legs to shear off and the clips to cause a short to ground. Next job is to try and explain that to the courier before having both inverters shipped back up here for repair..... At least it looks like my design is in the clear!!
Logged
rogeriko
Hero Member
*****
Offline Offline

Posts: 1387



WWW
« Reply #11 on: May 17, 2019, 08:34:11 PM »


Rogeriko - It's quite acceptable to parallel inverters up. I have an installation I look after with 3 WB 3800s per grid phase paralleled up on the rectified DC input from turbine - no isloation transformers there. Also if paralleling Auroras, only n-1 of the inverters need an isolation transformer, so a 3 phase install would only have them on 2 phases.


If you have 3 windyboys one on each phase then of course they are completely isolated from each other that has nothing to do with this installation. Lets hope the courier reimburses you for the damage and you can buy one 6kw inverter and its job done.
Logged

floydy
Newbie
*
Offline Offline

Posts: 6


« Reply #12 on: May 18, 2019, 10:21:13 AM »

If I can repair them it'll be fine in the original configuration anyhow! I've tried a claim to the courier anyway.

The early auroras are really tricky to repair without damaging the PCBs - the IGBTs are soldered to the board and conduct their heat through the PCB to the heatsink. I've never seen another design do this - the later ones saw sense and have them on the heatsink more conventionally! It normally seems to be the IGBTs that give up when a ground fault occurs, hopefully not too much else.
Logged
biff
Global Moderator
Hero Member
*****
Offline Offline

Posts: 11878


An unpaid Navitron volunteer who lives off-grid.


« Reply #13 on: May 18, 2019, 11:07:59 AM »

Scruffy  Brudder.
        Where art though.  ?
Someone is singing your songs
          Biff
Logged

An unpaid Navitron volunteer,who has been living off-grid,powered by wind and solar,each year better than the last one.
floydy
Newbie
*
Offline Offline

Posts: 6


« Reply #14 on: May 18, 2019, 10:52:38 PM »

rogeriko - What I was saying re 3 windy boys is totally relevant, but perhaps it wasn't very clear. The installation is a 20kw turbine running a total of 7 windy boys from memory. They are all paralleled on the DC side straight off the rectifier, and spread across 3 grid phases. There's no need for isolation transformers on windy boy inverters. The inbuilt transformer is isolated.

I'll post a pic of the Aurora and WB up and running once repaired. 6kw Auroras are becoming v. hard to find now - this is a solution that gives the benefits of the low voltage start up at a far lower cost than even a single 6Kw windy boy. Something like 300 in 2nd hand inverters and a bit of programming, vs 1800 for new Aurora 6kw. If you're not trying to extract any power sub 200V then a couple of second had sunny boy 3000s will do the job for less money still!
Logged
Pages: [1] 2   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.20 | SMF © 2013, Simple Machines
SMFAds for Free Forums
Simple Audio Video Embedder
Valid XHTML 1.0! Valid CSS!