Re: [RE-wrenches] feed-in imbalance

[Jamie Johnson]

Marco,

 

I believe some of the discussions in the past had to do with the old 6kW imbalance limit that is used by several utilities on a 120/240 small residential single phase transformer. (don't remember the CA utility that came up with this)

I had this discussion with our local utility (FPL) recently and they look at it on a case by case basis due to the many variables involved with 3 phase power distribution, such as the size and type of transformer(s), 3 phase loads on the premises, the harmonic distortion if any on a shared 3 phase transformer, core saturation, load balancing, etc.

 

If you install a system in the FPL service area that is not balanced and either the harmonics or voltage is out of spec as a result (yes, they do test them), then you basically have 2 choices, balance the system or pay to upgrade the service drop and transformer.

 

There has been talk of testing various 3 phase transformer(s) to determine the maximum/safe out of balance configuration by our local utility, however, again there are a lot of variables, so it would be difficult to cover every scenario.  And this usually is only an issue on small 3 phase transformer(s).

 

I think that the 8,9,10TL 208v inverter has a load limiting ability that is incorporated in the inverter when you install 2 or more inverters, and it is programmable to limit the output of a single inverter to 6kW.  I believe you have to purchase the additional communication cables from SMA (cables available after the first of the year? or so I have been told).  Also, the design parameters seem a bit limited on the TL's.

 

Jamie

 

 

-------- Original Message --------
Subject: [RE-wrenches] feed-in imbalance
From: "Marco Mangelsdorf" <ma...@pvthawaii.com>
Date: Fri, December 10, 2010 2:00 pm
To: "'RE-wrenches'" <re-wrenches@lists.re-wrenches.org>

Now that SMA has come up with their new 8, 9 and 10 kW transformerless line of single-phase 120/208V inverters, it brings up the question once again about how practical and wise it is to have one or two of these inverters feed into a three-phase service.  That is, is such an unbalanced feed much, if any, of a big deal?

 

I spoke to my consulting E.E. about this and he said that the large majority of utility-provided transformers are so large these days that an unbalanced feed of, say, a 10 kW inverter that only has output power through L1 and L2 should not present a problem.

 

Any other thoughts out there on this matter?

 

Thanks,

marco

 

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