Single phase inverter connection to 3phase power

[Richard Borck]

I'm making a connection to 3phase 208v. power at a restaurant with my 4.2 Aurora Power One Single Phase Inverter.

Have certifications to make this connection from manufacture, but local permits dept is telling me I'm not complying with nec 690.63A
But as far as I can tell I am.
Any comments??

Richard Borck, Pres.
Premier Homes, LLC

 

[ggunn]

I'm making a connection to 3phase 208v. power at a restaurant with my 4.2 Aurora Power One Single Phase Inverter.

Have certifications to make this connection from manufacture, but local permits dept is telling me I'm not complying with nec 690.63A
But as far as I can tell I am.
Any comments??

Richard Borck, Pres.
Premier Homes, LLC

Did they tell you precisely what aspect of the rule you would be violating? Just flatly telling you that you are in violation isn't very helpful.

 

[Richard Borck]

Thanks, yea, they are not helping as much as they think. I'll have to ask them to be more specific.

 

[Jraef]

NEC 2008 690.63(A):

Single-phase inverters for photovoltaic systems and ac modules in interactive solar photovoltaic systems shall not be connected to 3-phase power systems unless the interconnected system is designed so that significant unbalanced voltages cannot result.

So without our knowing anything about your installation, how do you think your system relates to this requirement?

 

[nakulak]

seems like aurora would have sold you a Trio for this application

 

[Richard Borck]

More specs for my issues are:

More specs for my issues are:

Thanks Jraef and Nakulak for your comments...
I have a 4kw urban green energy wind turbine. The inverter is part of a package from manufacture. The 3 phase connection is a fix, due to fact can't get a 3phase inverter this small.
10kw is smallest I'm aware of, plus I'm trying to resolve this issue without additional charges to my client. So getting a 10 kw 3 phase inverter, unfortunately is not one of the solutions.

Inverter co. Says their inverter mimics the grid connection. So I'm not sure there is any problem with unbalanced loads. NEC, doesn't seem to address what exactly is considered an unbalanced load.
inverter Co. Says an unbalance would not occurred until after at least 6kw of difference.
The wind turbine only generates 4kw at 25mph, and we only have a consistent 12 mph typically and this site in particular about 10mph, therefore I don't see how in the world, my connection with this wind turbine could possibly cause an unbalance that would be of any concern, or not meet NEC 690.63a.

Still need help, cause local utility said today. Richard this is a 3phase 120/208 v service!

So now what??

 

[Richard Borck]

NEC 2008 690.63(A):



So without our knowing anything about your installation, how do you think your system relates to this requirement?

I think that the inverter is not providing "any significant unbalanced voltages" to the system.
This is what I understand from Power One. It would be good to know what NEC has determined or how they define a "significant voltage unbalance" Power One defines it as greater than 6kw.

 

[jaggedben]

I may not be recalling correctly, but I believe there is an IEEE standard that calls for voltage imbalances between phases to be less than 2%. Your utility may have its own standard. Maybe out there on the islands they would have less ability to adjust to voltage imbalances than on a larger grid.

Bottom line, I think it is incumbent upon you to calculate what the max voltage imbalance would be and make an argument to the utility as to why it would not be 'significant'.

 

[jaggedben]

The NEC doesn't define a "significant voltage unbalance", all it says is that you can't have one. You will have to look for standards contained in other codes. As I see, what the NEC says is "don't connect a single phase inverter to a 3 phase system unless you have done calcs and gotten approval on those calcs."

Power One defines it as greater than 6kw.

Which hardly makes a whole lot of sense, because kilowatts aren't a measure of voltage. As I understand it, delta-V depends on a number of factors, but mostly the size and length of the conductors going back to the transformer.

 

[masonc]

The NEC refers to voltage imbalances, but anyone who knows much about grid-interconnected inverters knows they do not create voltage at all, they produce current, In fact, they disconnect if the grid voltage varies outside strict parameters.
The voltage is set by the grid, the inverters measures the grid voltage and pushes current back into the system. Only in the case of where there is high conductor resistance are you likely to see voltage rises as the current from the inverter causes a local voltage variation.
A 4KW inverter properly connected to a sizeable utility grid is not going to raise the system voltage.

Chris Mason
Comet Systems

 

[Richard Borck]

Inverter voltage

Inverter voltage

Thanks Chris,
Exactly what Power One said in our last conversation, 11-4-11

Now, I'm trying to get a local engineer to agree and write up a short report on this connection and how it relates to NEC - hopefully they can state I'm in compliance with this connection and that no imbalance between phases will occur due to this installation.

As it is now, the local utility and building dept officials claim that I'm not in compliance - or they can't tell if I am in complaince with NEC, and I'm to proove it to them. Until then...
They have made my client request a waiver - which they approvedto which I think is a dis service to the general public

Grid on our island is about 55 megawatts.

RB