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johnjaymack avatar image
johnjaymack asked

ESS, LOM, and Feeding from DC to grid not allowed

I am currently using two Multiplus-II 24v/3000 2x120 inverters in parallel. From the manual, the following are the two types of internal relay connections, one for single phase and one for split phase. This is single phase.

1697240956063.pngAnd this is split phase.

1697241079634.png

In the Ve Configure 3, the grid type selection is None - (feeding energy from DC to grid is not allowed). In this configuration, the inverters will provide power assist when incoming power is insufficient either on all output legs when the incoming power is single phase, and to leg one only when connected to split phase incoming power. In this configuration, the Inverter MUST provide anti-islanding LOM functionality to be legal. This point is important.

In this configuration, the automated generator control will work, but there is no warm up and cool time functionality.

To get generator Warm up and Cool down functionality, ESS must be enabled. But if ESS is enabled, the inverter apparently loses its anti-islanding, LOM functionality. The FAQ states in one part:

Q2: Can I use ESS in a vehicle or a boat?

A: No you cannot. After unplugging the shore cord it can take up to a few seconds for the system to detect the loss of mains and open the back-feed relay. During those seconds, the shore power plug will be `live`: there is 230 Volts AC on the terminals. The exact number of seconds differs per country and depends on the local requirements.

The same applies to other solution where the wiring is not protected against accidental removing, for example a simple cable with end-user removable plug, such as a portable power supply.

Q3: Can I use ESS with a generator?

A: Yes you can. Note that the only installation type where that makes sense is a land based installation (no boat, and no vehicle). A Quattro must be used with AC input 1 connected to the generator, and AC input 2 connected to the grid. The role of the generator will be to provide power during a long grid failure.

Some, bigger or better quality generators, will be able to work with LOM Type B. For other less stable generators it will be required to disable LOM entirely. In that case make the installation such that it is still safe: no simple extensions cords, use enclosed wiring cabinets with warnings on the outside and/or an external ENS.

Note that it is also possible for some generators that it is not accepted by the inverter/charger at all, unless very specific grid codes are chosen. See the section “Disabling LOM” above for details.

More information about Victron Inverter/chargers combined with Generators is in the MultiPlus Generator FAQ.

Q4: I use ESS, but have disabled feed-back, is a grid-code still required?

A: Yes, also in this case LOM is required to make for a safe and also local regulations compliant system. Running ESS with disabled-feed-back is still not the same as using a Multi in its default configuration without ESS.

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Now VE Configure ALWAYS seems to assume that the inverter being used is Quattro with two AC inputs. The Multiplus II only has a single AC Input. But this does not change the requirements for LOM.

So here is the basic question. If the LOM function is good enough and legal to use when the inverter is told not to supply DC power to the grid, Why is the LOM not good enough to allow ESS use and define zero DC feed to the grid?

Remember that in answer Q2, "No you cannot. After unplugging the shore cord it can take up to a few seconds for the system to detect the loss of mains and open the back-feed relay." Is ESS disabling proper LOM functionality, is proper LOM functionality working and using ESS changes recommendations to a more conservative value, or is LOM functionality not working properly even when ESS is not enabled and the plug connections may be energized for a few seconds even in the "the grid type selection is None - (feeding energy from DC to grid is not allowed)."

Something does not make sense. I would like a clear explanation. Maybe someone for the mother ship can explain the apparent contradiction in operation.

ess settings
1697240956063.png (27.4 KiB)
1697241079634.png (30.3 KiB)
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3 Answers
Alexandra avatar image
Alexandra answered ·

@JohnJayMack

To run ESS a grid code must be selected. So it must comply to that standard and be a fixed install. If people are not following that then it is on them. The warnings are there.


Grid code - feeding from DC not allowed -does not allow feedback and does not allow the ESS assistant to be programmed at all.


Grid code other allows the user to alter LOM detection and even disable it. So you will be non compliant. And if it is not a fixed install (because of feedback) there can be dangerous voltages at the input for a few seconds before relays open.

If you need generator warm up and cool down then assistant/relay programming (or going back to the good old days) is what you need to do.

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johnjaymack avatar image
johnjaymack answered ·

Thank you @Alexandra for the response. I have asked another question that I would like you to look at entitled:

ESS, LOM, and Feeding from DC to grid not allowed

In that question, I have pointed out an inconsistency in the operation and documentation. To summarize, the connections of the inverter are the same whether used in a No Power fed back to the Grid and in a grid-tie usage. In a No Power fed back, the Inverter evidently has a Code Approved Loss of Mains function to disconnect the internal transfer switch from the external power source if the external power is lost. This code approved LOM function disappears if ESS is activated.

You wrote "Grid code other allows the user to alter LOM detection and even disable it." If this is the case, the LOM configuration that exists for "feeding from DC not allowed" should be available and using that configuration for LOM should give the same code compliant behavior as using grid code " feeding from DC not allowed."

I guess my basic question is how the LOM function is good enough for non-ESS use but is not good enough if ESS is enabled. The physical external connections are the same and the internal transfer switch is the same. In normal use, if the incoming power is insufficient for the load, the inverter will use DC battery power to increase the output. This is called an "assist function." In this case, the inverter power is running in parallel to the incoming power. If the shore power fails or is removed at this point in time, the internal transfer switch must detect the LOM and drop immediately. If it does not, then DC power inverted to AC will be present on the incoming plug. From my reading of the literature, the Multiplus II, in non-ESS mode, will prevent the problem. But turn ESS on and suddenly the LOM is not capable of preventing this issue.

I wonder if this is a case of different internal departments at Victron not communicating with each other. The department responsible for the non-grid-tie use have determined that the LOM function is code compliant. Thus, my use without ESS is "safe." The department responsible for grid-tie use looked at the same LOM function and decided that in a grid-tie application, the LOM function does not meet code.

I spent 40 years in the Elevator industry and personally know of at least one instance where two engineers at the same company sitting side by side came to opposite conclusions regarding code approvable for a passenger elevator control system. After a conference, an agreement was made.

I may have over simplified this issue and I hope someone can help make it clearer.

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Alexandra avatar image Alexandra ♦ commented ·

Probably are overthinking it.

But it is to do with local regulations the grid code thing. While some of what Victron does is to meet requirements, the rest is up to the installer to be compliant with how they implement the system.

The way the inverter works is not the same between an ESS and non ESS system as the system 'pushes' back against the grid and if it can 'frequency shift' the grid it disconnects as it sees the grid as weak (LOM detection). Where as on a basic system it does not do the 'push' back. Hence the possibility of live power at the terminals in the ESS system and why it must be implemented in a fixed install.

If you have every used LOM on a generator and then disabled it with an ESS system you will hear what I am referring to.

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johnjaymack avatar image
johnjaymack answered ·

Thank you for staying with me, @Alexandra. Your response caused me to dig a little deeper into the manuals. I interpret from some research that in the "None" setting for grid code, the Multi monitors grid current and only inverts to boost output power when input power is insufficient. This is probably not consider a true LOM function.

It is sad that using a generator properly meaning being able to warm the generator up before a load is applied, and cooling the generator off with no load before turning the generator off is only available when ESS is enabled. I am using the Color Console to monitor and control my system. The Generator control is very robust, but significantly lacks the warmup and cool down functions without ESS enabled. I can and will hack the system to gain these functions, but it seems to be an oversite not to provide the functionality in the basic generator control.

I may try ESS since I may have external LOM functionality already in place. If I do try the ESS functionality, I will take responsibility for the safe operation.

Also, I will have to test to see if the Ignore AC 1 must be enacted of just one inverter as the manual suggests, or must be enacted on both inverters as you suggest. Once again, thanks for your help.

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