Hi.
im reading a lot about the Anti-islanging (ns-protection) (na-schutz in german) device, like the Ziehl UFR1001E device, and i read that the multiplus 2 even has such an anti islanding device inbuilt.
Now: i also read that every multiplus has a LOM integration that practically does the same: disconnecting the inverter and thus discontinuing the feed-in to the grid, in case of a grid failure.
so my question: why do we need both, LOM and Anti-islanding (ns-protection)?
is it because Anti-islanding is redundant by having two relays connected in series?
Why doesnt LOM has two relays to begin with?
EDIT: Found some interesting infos about LOM:
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.
