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Anti-Islanding devices?


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Hi all,


I'm playing with Victron's Hub-1 setup at the moment, but to really make it safe I need to add an anti-islanding device: Something that will disconnect the grid if the grid goes down.


From what I can see, this isn't an easy problem to solve in a generic manner, mostly because of the dead zone (when your incoming power is balanced very closely with your consumption). I haven't been able to find any commercial devices (except for a company in Germany) to do this sort of thing.


One guy used two series-wired contactors for the job, powering the coil from the mains. The idea is that if the mains drops out, the contactor should disconnect. I'm worried that feeding back enough power might be sufficient to keep the contactors closed, that is: I don't see how the contactor cannot accidentally be powered by feedback power.


Any advice would be appreciated.



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What invertor you planning on using?

Only reason I ask, is because only Grid Tied Invertors can be connected directly to the grid. Any other invertor will blow itself up if you connect it directly to the grid.


Getting back to your question regarding the contactor,

Yes, it would work. For your invertor to keep the contator closed during a power failure, your invertor would need to supply enough power, to power the rest of the grid :)

That should be one beefy setup :D

Now, allthough this solution might work in practice, legally this is not allowed, as the contactor might fail in the closed position, resulting in somebody's death :(

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To answer the first question: Yes, traditionally only the GTIs can be connected to the grid. But Victron has done something really amazing and all quatro and multiplus inverters are supported. You can run it in hub configuration where it can run connected to the grid, exporting power. So to answer your question: I have a Victron Multiplus, and I want to use a hub configuration. Perhaps not immediately... I'm doing the research for the moment :-)


What I really want to do is export just enough to power the rest of the house without any of it actually getting out on the grid. Confusing? Let me explain. Like many people, my inverter feeds only some circuits in the house, leaving the rest to run from the grid only. In other words, there is somewhere I can export electricity to where it can be used by myself (before the inverter, but after the grid connection), before it ends up going out on the grid (which I don't want, because I have a dumb prepaid meter).


But I must have a anti-islanding device for this to be even half-legal.


I ideally want a current sensor on the main incoming line, and I want the software in the inverter to balance things so that current on the incoming line hovers just above zero, thereby avoiding export. If I can convince someone at Victron to write an assistant for this use case... I'll be in business, but this sort of thing only happens if enough people want it. In theory it should be possible: In hub-1 configuration the multiplus is in communication with the mppt controller and controls how much power is pushed onto the DC bus, son in theory all you have to do is balance this with whatever the sensor is telling you (plus a little extra to keep the batteries floated and compensate for losses).


Regarding the contactor solution: There is a specific case where it will fail, and which is unacceptable. Sure, if my whole neighbourhood (or just all the houses in my street on the same phase) go out, the grid would turn into a very low impedance load and it will trip out. But if the outage is caused by a problem a bit closer to my home, for example if the cable feeding my own home is severed, I could very likely end up energising my end of it, and because things are perfectly balanced, the contactor won't drop out.


The regulations also specify that you must have two series-configured issolators and at least one of them must be of the physical kind (the second may be solid-state), so in theory if two contactors in series could do the job it would be legal.


I found one anti-islanding device so far. I almost cannot believe that there's only one in the entire world. It's the ENS26, made by Ufe in Germany. I expect it to cost somewhere between R3000 and R7000, but I really have no idea, and even at the lower end it's a little expensive. ABB Also seems to make one (based on some pdf documents I found) but I cannot seem to find it in a catalog anywhere.

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It's relatively simple

Put a current sense on your grid side, electronics must monitor amps and if it exceeds rating of your system the grid contactor must drop out. Mean while power continues thru the inverter powered contactor to the house load.

the fact that the grid is down means that south africa is demanding power from you, excessive load. when you set the trip current it must supply the house and excess to the grid but any more than that it must drop the grid contactor out and protect the inverter and electricians working on the line. Extra electronics can be used to monitor a balance. IE Load is using 10A, inverter is supplying 20A and grid is taking 10A. 3 current sensors. now grid voltage goes down from eskom supply and grid becomes intensive load to your system. amp are up current load becomes excessive, contactor drops out. Now you monitor the grid voltage to see its down on the town side of the contactor. Make the contactor only pull back in when the town side voltage comes back up. It's a combination connect and disconnect for different reasons thru 2 or 3 contactors.


Just remember when all contactors are out, voltages can be picked up on both sides of the contactors to signal your electronics or power your contactors on when you want them on and off. when all contactors are in it acts as one line, so breaking the line momentarily and sensing voltage as there or not will work. As soon as the voltage is back from Eskom that contactor or relay in back in. Flip flop contactors can also be used and there are more angles that can be wangled out but at more cost and parts. hope this helps

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The problem remains with the edge case where your grid connection drops out without turning into a large power sink. Suppose the cable that feeds your house is severed for example. Your grid connection is now open circuit with a high impedance, causing no load on your system. If the technician comes to fix it, the wires will be live. If he does the right thing (which is to short the wires to ensure they are dead) I end up with possible equipment damage.


In the mean time I did find more anti-islanding devices. This one looks particularly good:




It complies with the German VDE 0126-1-1. It looks at changes in voltage and frequency, basically exactly the same thing that a Grid-tie inverter would do (though also monitoring rate of frequency drift is probably a good thing too).


That device is however still around 2k, shipping excluded.


I also noted that ABB makes one now, called the CM-UFD.M33. It's brand new, released in May this year. No idea what it costs.


There is also this one: http://www.shop.inelmatec.be/?product=g4pf33-1-230vac


Even more expensive though at 5.5k.


I think I'll postpone my hub-1 plans a bit and spend money on other things, like adding more panels or saving up for a better battery bank.

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Dear Plonkster,


Good post about Anti Islanding devices and  information. There are several Hub 1 Installations around South Africa and Namibia at the moment. The VEConfigure 3 software issues a warning to users and installers that a Anti Islanding device is needed when settings up the Hub 1 software configuration. Clearly you have seen this.


The Hub 1 Set up uses our Self Consumption Logic, if i can call it that. This means users optimize the the power they generate from their PV installation, in the case of a Hub 1 it is MPPTs. The Generated power is first used by the connected loads, then used to charge the battery bank and the balance is fed into the Grid. Inside the software set up there are 4 options on how the system should manage the grid connection and prioritize how the batteries are looked after, i am sure you have seen it under the switching policies. There is also a option not to feedback energy at all. Maybe that is the option for you?


if you have more questions please email me at [email protected]

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  • 2 weeks later...
  • 1 year later...

Any update on this topic?


Victron has an anti-islanding device as a complete pre-wired enclosure:


but it is VERY expensive (based on one local quote in Rand)


Eskom and various local municipalities specify NRS 097-2-1 which requires et al 2  breakers in series, one of which can be an internal solid state switch (the other must be electro-mechanical). From what I understand about the Victron Quattro, it has only one internal breaker, and therefore, although it can isolate the island in a grid abnormal condition state, it does note meet the requirement of NRS 097-2-1 and consequently a hub-1 configuration would not be legal without the anti-islanding device.


I need to have a grid connection for my Quattro (to supplement PV for self-consumption, not grid-feedback) and I am still searching for a reasonably priced solution.


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No update. The only device that meet specs and is somewhat readily available is the Ufe ENS26/27 devices and the UFR 1001 made by Ziehl. I got a quote on that before the Rand tanked (though of course it is permanently on a long-term-tanking-trip) and that was around 4k. I would expect 6k by now.


The only other thing that's changed in the mean time, is that some Victron inverters have gained Anti-Islanding as a standard feature. I have no idea which models has it, and if it complies with the standards.


I had much the same idea as you, to supplement rather than feedback. If you read Victron's self-consumption whitepaper, you are left with the impression that they can already do this. It practically urges you to buy an undersized inverter because of this supposed feature. If there is one thing I've been disappointed about... it is this.


In the mean time, things have changed. With the projected price increases from Eskom, I think it is better to spend the money on a larger inverter or more batteries than to mess with this stuff (or in other words, I've given up on this idea).

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plonkster, if I install a standalone grid tie inverter, e.g. Fronius, will I also need this anti islanding device? I thought that the inverter automatically disconnects should the grid supply fall away. Or is this not sufficient for NSR097?

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I've considered building my own :-) It's not trivial however. You have to consider three things: 1) Change in voltage, 2) Change in frequency, 3) rate of change of frequency (RoCoF). After all that, nobody is going to certify it as compliant anyway :-)

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I am also watching it all very closely. Instead of trying to be safe, all the loops and hoops with connecting to the grid, get as much off it as you can, wisely and cost effectively.


THINK it will work out cheaper in the long run.

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I investigated all and sundry, for most UPS'es at the time, was not designed to run 24/7/365. And solar controllers was a secret domain.


So UPS was out, there where no Axperts, and the Victron Phoenix 1600VA was about R8600.00 at the time. Made sense.


During the last few years, UPS's like Axpert / RCT/ Mecer / and few other names (for same device), got a huge boost and suddenly the game changed completely!


If I was buying today, AFTER reading all that is here, I would probably maybe consider a Axpert, because yes, the Victrons are not worth the extra cash today.


What I would LOVE to see in the next generation, is the same tech as what is in online UPS'es.

I hate the dips sometimes experience with inverters. As a matter of fact, my Victron feeds a online APC UPS because when all is working, and the fridge starts, I have a dip ... till the APC was introduced. It handles these dips when things start and stop like a master.


As a further matter of fact, I tried for a long time to get online UPS'es as the inverter. The problem with all of them was the battery voltages - moerse lot of 96v 9ah batts.

And having started on 12v, then moved over to 24v, going for 48v was the last ridge that broke the camels back. 96v batts, not a bloody chance.

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Plonky you not supposed to like the above post. You are the Victron champion.


Truth be told I like the Victron but price puts me off. Axperts may develop the reputation for being reliable but it is too early to tell. From the little reading that I have done it seems Axperts are being made with high end components so perhaps the initial hiccoughs they had are a thing of the past. 

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Plonky you not supposed to like the above post. You are the Victron champion.


Truth be told I like the Victron but price puts me off. Axperts may develop the reputation for being reliable but it is too early to tell. From the little reading that I have done it seems Axperts are being made with high end components so perhaps the initial hiccoughs they had are a thing of the past. 


Truth be told, I'm like the BMW fan who drives a 318 because that's all I can afford! :-P


Give props where it is due, I think. Price is definitely an obstacle. Sometimes it's not so bad. I paid 9k for a charge controller... it's a lot of money, but what else is there? There's the Microcare boikies, and there you're talking 7k or so if you want the same capacity. There's WRND, but they have limited open circuit voltages. Outback, Morningstar... those are all imports that aren't significantly cheaper if at all.


(That, and I started doing the research for building my own MPPT as a hobby, and realised that I'm probably going to spend 1.5k and more just in parts for a small unit...)


But then, as jou say, you also get the VE-Direct cable that costs R1050 (actual price from ExSolar a while back), which at present exchange rate should be closer to R700, but only because the original is like 45 Euro, which is also a little nuts. I'd actually buy it without complaining at R500.

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Buy an Axpert for R10k and they throw an inverter into the deal free! ;)


Only kidding but that is the reality with the Victron.


Sure, but the MPPT in the Axpert doesn't come close even to the Microcare!


It is definitely a case of paying double just because you want that little extra :-)

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Sure, it's getting a bit off topic :-) I'll keep it short.


Looking at the range of Axpert inverters and the MPPT in them, most of them have fairly low current and open-circuit voltage capabilities (25 amps, 70V-100V), and that limits what you can do with them. Some local people were selling the smaller models, and they are literally so limited that you can't put two >150W solar modules in series without exceeding the voltage limit.


Even my modest little system pushes over 30 amps and does voltages as high as 76V. So this isn't really a big criticism: A good MPPT just costs money. While toying with the idea of building my own, I realised that MOSFETs and Schottkys that does both high voltage and current isn't cheap, not to mention the big old inductor that you cannot buy off the shelf. The Axpert is cheaper, and this is one reason why :-)

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  • 2 years later...

plonkster and. others,


iam thinking of an anti_island system too, BUT that victron anti island thing is just like an under and over voltage checker with a relay , yes?

what if i place this :


and this 



does the same i think.. right?

ok, maybe not german ok, but still beter than nothing..


grtz kristof (belgium)

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1 hour ago, kg666 said:

victron anti island thing

They resell a device made by Ziehl. It's a passive anti-islanding device.

1 hour ago, kg666 said:

is just like an under and over voltage checker with a relay , yes?

It's a bit more than that. It checks...

  • Under- and overvoltage
  • On three phase systems, phase to neutral and phase to phase.
  • Under- and overfrequency
  • Vector shift (I'll explain below)
  • Rate of change of frequency (ROCOF)

The first three are self-explanatory, but the other two are interesting. First, the last one (ROCOF). The anti-islanding switch will allow the frequency to drift as long as it doesn't drift too fast. If the frequency shifts very quickly from 50hz to 51hz, that's a bad sign, and it will disconnect.

Finally, Vector shift. When a mechanical generator (eg Diesel) runs at a constant pace the AC waveform crosses the zero point exactly every 0.01 seconds. If there is a sudden change in load, the engine might speed up or slow down and this will cause the waveform to shift slightly and miss the expected crossing point by a measurable angle. If this is too much, the switch will disconnect.


The Ziehl has two internal relays (redundant setup). These are used to drive external contactors. When used with a Victron Multiplus, you only wire up one of the relays, as the inverter itself already has LOM detection (loss of mains), as well as active anti-islanding.

Active anti-islanding: This is where the inverter actively tries to create a frequency or vector shift, but cannot succeed as long as its connected to the grid. Most countries requires at least one active component in your anti-islanding setup.

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i understand plonkster....it must be doing more, lol because its 100times more money than the items in my link...

maybe i have to save and buy the ziehl island and some relay of 63a... , the packet that victron sells is way to expensive.. imo

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14 hours ago, kg666 said:

way too expensive

I had a quote from Ufe (another German company) for the ENS26, some years ago, and it was only a little cheaper. The ENS26 was also for the older German standard. There are others who make similar devices, ABB has one for example, but that costs even more than the Ziehl. I concluded that this kind of specialist equipment simply doesn't come cheap and that is that.

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