[RE-wrenches] feed-in imbalance
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 ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Options settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
Re: [RE-wrenches] feed-in imbalance
Marco, I believe some ofthe discussions in the past had to do with theold 6kW imbalance limit that is used by several utilities on a120/240 small residential single phase transformer. (don't remember the CA utility that came up with this) I had this discussion withour local utility (FPL) recently andthey look at iton a case by case basis due to the many variables involved with 3 phase power distribution, such as the size and typeof transformer(s), 3 phaseloads on the premises, the harmonic distortion if any on a shared 3 phase transformer, core saturation, load balancing,etc. If youinstall a system in the FPL service areathat is not balanced and eitherthe harmonics or voltageis out of spec as a result (yes, they do test them), then you basicallyhave 2 choices, balance the system or pay to upgrade the service drop andtransformer. 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 208vinverter hasa load limiting abilitythat 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 thefirst of the year? or so I have been told). Also,the design parametersseem a bit limited on the TL's. Jamie Original Message Subject: [RE-wrenches] feed-in imbalanceFrom: "Marco Mangelsdorf" ma...@pvthawaii.comDate: Fri, December 10, 2010 2:00 pmTo: "'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 ___List sponsored by Home Power magazineList Address: RE-wrenches@lists.re-wrenches.orgOptions settings:http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.orgList-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.orgList rules etiquette:www.re-wrenches.org/etiquette.htmCheck out participant bios:www.members.re-wrenches.org___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Options settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
Re: [RE-wrenches] feed-in imbalance
Marco, All 3-phase services, and single split-phase services has imbalances from time to time. The question of whether the imbalance is problematic depends on the size of the imbalance relative to the service transformer. Since 3-phase services are generally larger, a 10kW phase-to-phase connected single-phase inverter in unlikely to cause an imbalance problem unless it is indiscriminately placed on the service on the most lightly loaded phases. If the above inverter is placed on the two most heavily loaded phases (since it is a negative load), it will often reduce imbalance rather than increase imbalance. A load recorder placed on the service before construction can gather data so that when it comes time to choose the most heavily loaded phases, there is plenty of data to make that decision. The inverter in question has the same imbalance impact as a 10kW single-phase water heater on a 3-phase service. If the service utility requires a load analysis to add a water heater, then doing the same for PV is justified. If they don't require it, they should not require the analysis of the PV inverter. Bill. From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Marco Mangelsdorf Sent: Friday, December 10, 2010 11:01 AM To: 'RE-wrenches' Subject: [RE-wrenches] feed-in imbalance 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 ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Options settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
