'Islanding' a grid tie inverter ?

[Externet]

Hello all.
Am running a H6* grid-tied inverter from photovoltaic panels on my roof and injecting its generated AC output to the utility grid trough a 30 Amperes circuit breaker. No batteries, all is working fine, am really happy.

Grid <--------------------- 30A breaker at panel <------------------------- H6 inverter <------------------------ PV panels.

From what I understand, this inverter type only outputs power if the utility grid is present and working fine. How does the sensing, do not know.
Of course, the breaker panel supplies all my house and energy excedent is fed back into the utility grid.

If instead of the 30A breaker; a tiny isolation plain AC transformer** was used just to make the grid parameters 'presence' known to the H6 inverter (showing perfectly accurate grid AC voltage and grid AC frequency to the inverter) But totally incapable of injecting meaningful power onto the grid.

Grid -------------------> tiny 1:1 transformer---------------X--------------- H6 inverter <----------------------- PV panels

Can the point 'X' supply the inverted not-from-grid energy to a dwelling ?
That is, the 'inverted' outputted energy to supply a house but not injected into the grid.
That is, the grid used only as enabling reins for the inverter.
That is, a grid controlled off-grid system.
Am not after this configuration, just trying to learn hidden cracks and inner workings.

* H6 ----> https://shop.signaturesolar.us/products/6kw-120-240v-grid-tie-inverter-by-delta
**Similar to ----> https://www.ebay.com/p/14026121495?iid=252100975003

 

[betwixt]

Not normally but I'm not familiar with your particular model. The grid tied inverters continuously monitor the line so the anti-islanding can operate almost instantly. The danger if it didn't would be that you could electrify a broken cable from your end and electrocute a linesman fixing a break. They normally only provide a slightly higher voltage than the incoming line so they inject above mains voltage on your side of the meter. They can't normally work as a power source in their own right.

I have a somewhat similar requirement here, the incoming line is unreliable, when it works my GT inverter pushes out about 2KW but when it fails I rely on a big Diesel generator. Because the Diesel speed varies under load, the inverter can't keep track of it and stays off-line. I've been thinking of buying a big pure-sine inverter and powering it from the generator so it gives a stable frequency out, then supplementing it with the PV inverter. It will be an
expensive mistake if it doesn't work though.

Brian.

 

[Externet]

Thanks.
Fully agreed, the person working on the high tension lines could electrocute if the anti 'islanding' mode fails or is tampered with. That is not a plan.

What about the impedance of such tiny transformer and its effects on the utility grid ??? ... am trying to grasp the theorical consequences...

If a grid-tied inverter has a failure in its anti 'islanding' and a -say- 1000 Ohm to 1000 Ohm 240VAC to 240 VAC tiny transformer of a fraction of a Watt capability feeds back into the grid the inverted 240VAC...

240VAC from inverter output------------------->1K:1K transf.-------------------->feeding the 240VAC neighborhood grid and a deenergized 13KV pole transformer.

Wouldn't the secondary of the tiny transformer collapse its voltage to almost nothing by the huge load the grid presents to it, barely applying any potential to the grid ?
Repeating, that is not the plan but trying to learn what would be the behavior/consequences

 

[Easy peasy]

You can can only run a grid tied inverter, "stand alone " or "islanded" if it is designed to do so,

most grid tied inverters shove a sine wave of current into the mains, they need to see the mains is there before they'll do that,

they are not designed to provide a nice sine wave of voltage to a bunch of random loads ....

 

[FvM]

If the inverter has correctly designed anti-islanding control, it can be expected to shut down in your setup, the latest if some amount of load is switched to your local net. Most likely it won't even start because the reactive current drawn by the grid-tied inverter will be sufficient to change the faked grid voltage.