Loss of mains detection

Can somebody please educate me on why loss of mains detection is needed.

The inverter disconnects from the grid supply when your voltage goes below 195V anyway. So it would seem that function does what the LOM does anyway?

The only possible reason I could think that it is needed is when there is other equipment in your area feeding back and they keep the output voltage above 195V in a grid loss.

Or what am I missing?

Are you asking about the built-in Loss of Mains detection (LOM) in Victron devices or why is a device like a Carlo Gavazzi ET112 needed?

There’s some info here that explains LOM and the role of the grid code : VEConfigure: grid codes & loss of mains detection [Victron Energy]

I am talking about the built in LOM detection in the multis. Specifcally the 2 more advanced LOM detections that tries to shift the frequency to see if it is still connected to the grid.

The question is - why does it need something complicated like that to detect that the grid is off. Isnt it enough to just detect the input AC voltage.

I have read all the victron stuff about it but cant understand why it is needed over and above just detecting the grid voltage.

Well, effectively the input and the output are connected together in this situation (grid-connected), so it’s kinda difficult to only measure the input voltage alone. Aside from that, the complicated part is probably already part of the control loop to sync with the grid.

Shortest answer, NRS requires that mechanism for compliance. The inverter tries to push the grid out of phase. Because it’s too weak it won’t succeed, unless the grid fails. According to them it’s the quickest way to determine a grid failure without waiting for the inverter to sense the Voltage drop.

Trying to explain this in the simplest way i know to do it, the clever boys should add/correct me if i am wrong in my explanation.

@plonkster ?


Yeah, Jaco’s got it, more or less. I’m not sure if Loss of Mains (LOM) detection is an industry name or more of an internal Victron thing, but it comes down to the same thing.

All the grid codes in the world that allow for distributed generation require that a device detects that there is a loss of mains, and then takes action to prevent islanding.

Islanding happens when a group of inverters start mistaking each other for a grid connection, and forms a little powered island in a sea of dead grid, potentially endangering people who has to work on that grid.

I don’t know if you’ve ever heard this line of argument, but I remember it coming by often on the other forum: Someone would say that it is easy, just connect a contactor to the Eskom side, and if Eskom fails, the contactor drops out and you are disconnected! Voila!

Well, no, if you have a group of inverters making enough power, they will also hold that contactor in.

So how do you know? Well, there are several ways.

Some are passive measures. Those are watching the frequency and the voltage, for example. Sudden changes in voltage or frequency (called a vector shift) may indicate an islanding event, and will cause the inverter to disconnect, and then monitor the connection for 60 seconds before reconnecting. A more advanced one is called RoCoF, it measures the second derivative, the rate of change of frequency. It is okay if the frequency changes, but if it changes too quickly (even if it remains within range), you also trip.

Other measures are active measures, and Jaco already alluded to one. You actively try to speed up or slow down the grid frequency. The grid is way too heavy to yield to the tiny force of a small inverter, so normally it doesn’t succeed, but if the grid falls out, your collection of distributed generators made by different manufacturers immediately destabilise things quickly enough that one of the passive methods picks it up.

So with all that rambling out of the way: Depending on how sensitive you need it to be, you pick an LOM setting when you configure your Multi or Quattro. For SA, type B is sufficient (type A is more sensitive). If you turn it off completely, the Multi still employs passive methods of detecting an outage, but it isn’t sensitive enough to comply with NRS097.

But of course sensitive LOM settings sometimes cause heartache with generators that might not have a clean signal, so you may want to use a less sensitive setting if you have such a thing.


And since we’re now discussing this, I’d like to quickly touch again on the topic of Frankfort and why Eskom forced them to implement load shedding despite their sizeable distributed generation.

Because the equipment they use very likely has anti-islanding of some sort, it means that a large disaster (the kind that could cause a complete blackout) will probably be felt by distributed generators, they will see a sudden change in frequency or voltage, and they will disconnect, as designed.

The generator will literally trip.

When a generator trips, the remaining ones immediately has to pick up the load.

That means that if the DG at Frankfort trips, Eskom immediately has to pick up the load. And they were not happy about that added risk.

What I understand from your explanation is that Frankfort could disconnect from the grid due to anti-islanding measures it has to have in place. How would it then be possible for Eskom to have to pick up the load? There’d be no connection to the grid?

Are you saying the the DG isn’t sitting in front of Eskom and the loads it is powering (i.e. loads are on the output of the DG), it is sitting parallel with Eskom to the loads. So the DG can still trip and the loads would remain connected to Eskom?

Aha this is what I wanted to know. Now the LOM with phase shifting makes sense. Several inverters together in an area could potentially keep each others AC inputs live since they keep the voltage up.

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Sorry for not answering the question, but I am not in tune with the exact circumstances.
Frankfort won’t be able to dictate unless they have the wherewithal to go off-grid.
Otherwise, they are just a larger version of any domestic user with some solar.

That said, I can’t help but think this caper was allowed to become an adversarial standoff.
I think the community could still gain concessions with a more cooperative stance.
That ship may have sailed, but I hope not.

Correct. This is what I am saying.

Also correct. But as I understand it, they need slightly more battery capacity (they already have a big bank), and they need to comply with NRS048.

I wasn’t aware they had a battery, the article I read indicated they hadn’t.
Edit: Another recent article indicates an expectation that ESKOM stores the power as a point of contention.

Mmmh. For some reason I thought they have some battery capacity already. It appears I was wrong about that. The media did however say they would have to add battery capacity to get around it.

Edit: Or not… see post below :slight_smile:

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The “Frankfort PV Independent Power Project” apparently has a PV capacity of about 3.8MW and 1MWh battery (solarMD if curious)

Frankfort apparently has a peak load of around 6.5MW.

The major bone of contection was around → Instead of switching off the entire town of Frankfort, it has divided it into four main zones, with zones being switched off for one-and-a-half to two hours instead of the ‘standard’ two to two-and-half hours, as is the case in the rest of the country.

Eskom said problems between the two parties emerged when RFS introduced “voiding”, a term created by RFS to describe a situation where it did not implement load-shedding as per the approved schedules during daytime hours when its solar PV plant was in optimal operation.

Responding to a claim that Frankfort had been forced to dump excess solar power generated by the plant, Eskom said: “Assuming their dumping claim is true, we met with Rural Maintenance twice in May and presented them with our standard offer. This entails that we wish to buy any excess electricity generated by their plant.”


I think the real issue with Frankfort is that they did not generate enough power to offset the savings that loadshedding would give Eskom. I believe for their proposal to work, they would essentially have to island themselves during loadshedding, which they clearly don’t have enough grid-forming capacity for.

(Eskom also argued that the PV plant is already part of Eskom’s base generation and cannot be used to offset loadshedding.)


Unless they (Eskom) used the savings outside “Frankfort Hours” to help another areas. Eskom has played a nice political game here and as much as RFS didn’t follow process I feel Eskom is achieving their objective - scare off others for the moment and delay the big move to RE (IPP’s).

The Cape Town drive will be very interesting to follow…

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I really don’t think they have given it that much thought (or even have the capacity).

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But would this trip of their Solar Farm/Batteries and the impact of this tripping me very similar to a major transformer trip as far as Eskom is concerned, where they see the entire town drop of the grid.


No, the town wouldn’t drop from the grid because the town isn’t on the output of the generation. The generation is parallel with Eskom to the town. I assume they couldn’t “rewire” the town to feed from one supply line only and therefore had to opt for the parallel route. :man_shrugging:

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