 Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me. |
Forum Index : Other Stuff : 3 phase mains questions
| Author | Message | ||||
| domwild Guru  Joined: 16/12/2005 Location: AustraliaPosts: 873 |
Hi, Have just learnt something: If you are feeding a three-phase mains supply from PV you need three inverters plus balancer; presumably to balance the phases. Just looking at a new 6,000W SMA SMC6000A solar inverter with balancer, three sold at auction for $800-$1,300 each. New price of this discontinued model was US$3,000? A few questions relating to a Perth three-phase mains supply if I may: 1. How is the three-phase power cut at the meter with the mains switch? As the switch is only small, does it cut the neutral line? 2. Is it the same at my fuse box? 3. How are all the three phases balanced load-wise as the power circuit would be the largest load and the light circuit the smallest perhaps, do they split the power circuit two- or three-ways? Or does the power station hope with every electrician connecting the circuits at random for every house, in the end all three phases are balanced anyway? My wife reported a power failure in Forrestfield (WA) messing up her doctor's appointment and judging by our power policy shambles, we can expect a few more of them. 4. Am dreaming of connecting my generator to one power circuit, does that mean I may have power to our fridge but no light? With the mains switch off at the fuse box, will it be safe or will there still be some back feeding to an unhappy lines man? Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up. Winston Churchill |
||||
Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Hi Dom No, all 3 phases are switched off, switching the neutral wont work. Yes a 3 phase mains switch is surprisingly small. 3 phase is a much more complicated and dangerous beast than single phase. Dont touch it, get a sparkie. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
||||
Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
Sound advice there from Glenn. From your questions its quite clear that tinkering with 3 phase mains might be a bad idea for you. Its not something you can learn here, there is a reason for the lengthy apprenticeship electricians have to to do to qualify. Klaus |
||||
| domwild Guru Joined: 16/12/2005 Location: AustraliaPosts: 873 |
Thanks for answers. Any idea how the balancing is done is done at the home or is it only factories as big consumers which have to balance or get penalised? With SMA building solar inverters with balancers, it looks like as if in the EU even a home is expected to balance to the net on all three phases supply-wise? Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up. Winston Churchill |
||||
| Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
Well, the way I learned it - a very long time ago - there are a number of fuses/ C/B's in your meter box. Each protects a 'circuit' of expected loads. The 'circuits' are connected to an individual phase so that the expected loads on each of the three phases are roughly equal. They are almost never exactly equal as not all loads are on at the same time. This is for single phase loads, connected between a phase & neutral. Klaus |
||||
| domwild Guru Joined: 16/12/2005 Location: AustraliaPosts: 873 |
Thanks Tinker. Looks like in any single house all three phases are never loaded equally, but in the grand scheme of a suburb it may just balance out. As most suburban houses in Perth only have one inverter but are on a three-phase supply it looks like the electrician will most likely connect it to the circuit the fridge is on? Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up. Winston Churchill |
||||
| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
That is pretty much it. All three phases plus neutral are on the power pole out in the street. Each house is connected to a particular phase (could be any of the three). Some larger houses might get two phases. Large blocks of flats or home units often get all three phases if the total expected load is heavy enough. Over several streets with a large number of properties connected, the loading on each phase should pretty much balance out, though it will never be perfect. About the only reason you might want three phase at home is to run large motors. In that case you do need a proper three phase supply. If its just a very large number of individual single phase loads distributed between three phases, you could just use three inverters without any particular requirement for balancing or phase locking. Cheers, Tony. |
||||
yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
there are costs/penalties for having unbalanced or reactive and inductive loads on a three phase business or industrial connection these are usually waved on domestic systems but not always, it pays to talk with someone professional if the guff from the power retailer is not clear about this. Regarding inverters, SMA sell the tripower range of 3 phase inverters. They have have some really nice software that lets us customize the grid feed-in mix to avoid paying penalty rates when the house is drawing on one phase. Running three separate inverters is pretty old school on small solar systems, it is all in the one box these days. Have to admit it has been a while since I have played with a sunny tripower, my preference now would be to use a Fronius Symo. they are very good quality and have swap modules that are repairable onsite by a local techie. I'm confused, no wait... maybe I'm not... |
||||
| domwild Guru Joined: 16/12/2005 Location: AustraliaPosts: 873 |
Have Our area in Perth has just received a new meter with screen, the kind of meter, that has been in Vic. for a long time. Noticed three large 100A fuses below the meter, so it looks like I am getting all three phases at least past the meter. When I looked at the stove, I noticed two phases going in. Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up. Winston Churchill |
||||
rustyrod Senior Member  Joined: 08/11/2014 Location: AustraliaPosts: 121 |
My power box has a 3 phase power point (nothing plugged into it) One phase is connected to the house and the grid tie at the house. One phase is connected to the oven. One phase is connected to the night rate off peak hot water and is not used any more, note the meter uses one unit every quarter to power it's self which I pay for! The three phase meter indicates I use power from all three phases adding up to my total power use. I had two phase disconnected after the meter to see if only one phase would be billed It made no difference with units being across all three phases. Very smart meter must switch between phases to supply one phase continually to the house! This meter also uses one unit per quarter to power itself which I pay for! Then they have the nerve to hit me with around $100 per quarter for a "service fee" In my box the three big 100 amp fuses do disconnect the mains so the sparky does not have to climb the pole to disconnect the power should it be necessary to work on the meters. Always Thinking |
||||
| yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
hi rustyrod, that sounds like a polyphase meter the way they are normally set up is the total of the imported from the three phases is summed together for the billing. In SA we are still allowed a 5kw inverter connected to a single phase, I think I heard it is a lot less than that in WA. Normally the replacement polyphase import/export meter can handle solar on a single phase or all the phases and it doesn't effect the credit received . Each house in the street is wired differently in a rotation to balance the load back to the grid. I poked my nose in a couple of powerboxes in my local town yesterday, the business connections here seem to be about 50/50 polyphase meters and three meter systems (one on each phase) I was hoping to chat with someone about their billing on the three meter system with solar to see if it has changed recently but I couldn't find anyone, they must have been all out to lunch. I'm confused, no wait... maybe I'm not... |
||||
| domwild Guru Joined: 16/12/2005 Location: AustraliaPosts: 873 |
Thanks for the many answers. I am definitely not going to fiddle with it myself. To get an export credit I would have to get a sparkie in, especially with the new "smart" meters. There is a rumour around, that the older "dumber" meters just ran backwards once illegally connected to mains, but this theory I would also not have tested! Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up. Winston Churchill |
||||
 Print this page |
