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domwild
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Joined: 16/12/2005
Location: Australia
Posts: 873

Posted: 01:41pm 24 Apr 2013

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Hi,

Not blessed with a black belt in electrickery: The grid ties in metro areas would be grid ties for three-phase mains. Am interested to know if all three phases are loaded equally or only one phase? That would lead to the phases being unequally loaded.

Can an installer find out the loading to get it right during installation of solar panels? Or are the inverters loading all three phases?

Different question:

As power fails in the bush frequently I may need to buy a generator at some stage. If I want to watch TV (sad addict) does the generator have to be a more expensive "inverter type" or a cheaper generator, which most likely generates only a modified sine wave instead of a pure sine. Am I right in assuming a TV needs a pure sine wave? Am I right in assuming an inverter-type gen comes up with a pure sine wave?

And do not worry, I am not going to kill a lines man.

Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up.

Winston Churchill

Downwind

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Joined: 09/09/2009
Location: Australia
Posts: 2333

Posted: 04:28pm 24 Apr 2013

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My GTI feeds in on one phase out of the 3 phase supply, this is normal and the smart meters average all 3 phase power in against the single output feed.

I would think the generator would be a pure sine wave where the inverters are not always.

Most TV's will run off a square wave just as well as a sine wave.

Sometimes it just works

Don B

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Joined: 27/09/2008
Location: Australia
Posts: 190

Posted: 10:03pm 01 May 2013

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Hi Domwild,

Most supplies to individual houses - even in metro areas - are only single phase. Unless you have a very large inverter (say above 5 kW), it will also be single phase irrespective of how many phases are actually connected to the premises. Power supply authorities are the ones who have to worry about trying to balance all of the single phase house supplies across their three phase street mains. They usually do this by connecting them to the three available phases in the order A, B, C, C, B, A as they progress down a street. This evens out the voltage drop on each phase.

Some appliances don't like "modified" sine wave supply, so the safest bet is a pure sine wave generator. The original Honda four stroke ones were very nice, quiet, and expensive. Now it seems that you have a much wider choice at a more reasonable price.

Regards

Don B

domwild
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Joined: 16/12/2005
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Posted: 01:03pm 02 May 2013

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Thanks, Don

Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up.

Winston Churchill

Warpspeed
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Joined: 09/08/2007
Location: Australia
Posts: 4406

Posted: 12:50pm 03 May 2013

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Don has nailed it.
Around here, in a typical suburban Melbourne street, you can walk down the road looking up at the five power wires strung between the power poles. (A, B, C, phases + neutral + usually a thin earth wire).

Most houses run from a single phase, some run two phases, usually when there is an electric stove installed.
Some properties have all three phases suppled, particularly if there are several flats our units crowded onto one suburban block.

True sine waves are mostly only needed with inductive loads such as motors or transformers, these can overheat or become unhappy with a square wave inverter, but not always.
Frequency can also be an issue, particularly a frequency lower than 50Hz, which is entirely possible with a small standby generator with a dodgy speed governor.

Most modern appliances these days use switching power supplies that are perfectly happy with square waves of any reasonable frequency and voltage.

I guess the golden rule is, does the appliance (whatever it is) have an electric motor or a transformer inside?

A TV set should work fine from either a square wave inverter or a small generator.

Cheers, �Tony.

PlanetPresident
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Joined: 18/07/2013
Location: United States
Posts: 5

Posted: 07:36pm 21 Jul 2013

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look at the extra cost of a pure sine wave inverter or generator as insurance, better to have it and not need it than to need it and not have it. If you go cheap you can always get another TV.

domwild
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Joined: 16/12/2005
Location: Australia
Posts: 873

Posted: 01:10pm 15 Sep 2013

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Thanks for answers. I remember hearing during engineering studies that factories have to ensure (with expensive equipment) that their draw or demand is balanced over all three phases. The power companies will insist on this requirement. Finding it interesting to read from Downwind that grid tie inverters are loading one phase only.

Our supply is three-phase, even in an outer suburban property but our bush block is on single-phase only.

Any idea what the power companies charge you for installing a smart meter if one wants to add a grid tie unit?

Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up.

Winston Churchill

domwild
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Joined: 16/12/2005
Location: Australia
Posts: 873

Posted: 01:15pm 15 Sep 2013

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In my last question I mean "smart meter" to be a meter, which is running backwards during a net supply from RE sources.

Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up.

Winston Churchill

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