3 ms·

Not sure sharing the neutral buys much as conductor size needs to go up vs just running separate wire. Most hybrid inverters now days are high frequency and ha

Not sure sharing the neutral buys much as conductor size needs to go up vs just running separate wire. Most hybrid inverters now days are high frequency and have a HVDC bus sitting between battery DC/DC, solar MPPT and AC inverter/converter. Since solar comes down from roof with HVDC it can be inverted without a transformer to AC then the LV battery uses a physically smaller HF transformer on the buck/boost to that bus. Seems to be lots of talk to tap that HVDC bus for say EV charging as its around 400v, also some inverters moving to HVDC batteries as well simplifying the DC/DC even more so. Could see a future where houses have a HVDC panel with battery, solar, inverter and EV charger hanging off it, perhaps even HVDC from pole with solid state transformers. If/when EV become popular then you will have much more readily available/cheap HVDC switching gear at 400/800v. Hard to beat the simplicity and reliability of AC using transformers though for distribution.

MisterTea 1y ago
> Not sure sharing the neutral buys much as conductor size needs to go up vs just running separate wire. The article mentions a system which will balance the shared current. But that sounds like needless complexity that was introduced to entice power companies by saving a few bucks not needing two insulators and conductors installed on each pole.
- aaronmdjones 1y ago
  > The article mentions a system which will balance the shared current. Not quite. It mentions the asymmetric Neutral current, and this is because in a balanced multiphase system, there is (almost) no current flowing on the neutral conductor, i.e. if you are consuming 10 amps from L1, 10 amps from L2, and 10 amps from L3, then there are zero amps flowing on Neutral. This is also why inherently-perfectly-balanced multi-phase loads (e.g. 3-phase motors with identical phase windings) can be constructed such that they do not require a Neutral connection at all. In the UK for example it's quite common that houses only get connected up to one of the phases, so if you have 60 houses on a street, 20 each would be connected to only L1, only L2, and only L3. This achieves a reasonable balance in practice; the current flowing on the street's Neutral conductor(s) is/are very small in comparison to the currents on the Line conductors. As in, it is already fairly well balanced, and there is nothing to be done in this regard. Within the single-phase installation the currents on Line and Neutral are of course equal under fault-free conditions (typically up to 100 amps for a residential installation). There's nothing you can do to reduce that. A lot of countries in mainland Europe wire up residential properties to all 3 phases (with much smaller permitted supply currents; I've seen as low as 20-amp main supply fuses), but again they go to some degree of effort to balance their phases with respect to single-phase loads. This is for grid stability reasons. For the street example again, they could have wired up every house identically, but connected the phases in a round-robin fashion, such that the socket outlet circuit(s) are on a different phase in each house, and so on. If there were ever a severe imbalance (which would be detected automatically, or by routine maintenance and inspection of distribution transformers, depending upon how bad it is), typically it would be arranged for some rebalancing work to be performed, for example by disconnecting an outgoing feeder line serving some dozen properties or more and rotating their phases (connecting the old outgoing L1 to the transformer's L2 output, L2 to L3, L3 to L1). This still maintains the phase rotation order (very important for 3-phase loads, like some EVSEs and motors) but allows a more equal distribution of loads. See https://docs.openenergymonitor.org/electricity-monitoring/ac-power-theory/3-phase-power.html https://docs.openenergymonitor.org/electricity-monitoring/ac... for why this is important. This is somewhat simplified though. Real-world loads vary their consumption dramatically, and also feature reactive components that shift the current forward or backward with respect to the voltage. A 10-amp capacitive load on L1 and L2 will not cancel out a 10-amp resistive load on L3. Harmonics are also a problem, as the article mentions.
  - MisterTea 1y ago
    Well aware of how three phase systems work. You're not guaranteed perfect balance which the article addresses by stating that DC current injection is monitored and controlled which is what I was referring to.

MisterTea 1y ago

> Not sure sharing the neutral buys much as conductor size needs to go up vs just running separate wire. The article mentions a system which will balance the shared current. But that sounds like needless complexity that was introduced to entice power companies by saving a few bucks not needing two insulators and conductors installed on each pole.

aaronmdjones 1y ago
> The article mentions a system which will balance the shared current. Not quite. It mentions the asymmetric Neutral current, and this is because in a balanced multiphase system, there is (almost) no current flowing on the neutral conductor, i.e. if you are consuming 10 amps from L1, 10 amps from L2, and 10 amps from L3, then there are zero amps flowing on Neutral. This is also why inherently-perfectly-balanced multi-phase loads (e.g. 3-phase motors with identical phase windings) can be constructed such that they do not require a Neutral connection at all. In the UK for example it's quite common that houses only get connected up to one of the phases, so if you have 60 houses on a street, 20 each would be connected to only L1, only L2, and only L3. This achieves a reasonable balance in practice; the current flowing on the street's Neutral conductor(s) is/are very small in comparison to the currents on the Line conductors. As in, it is already fairly well balanced, and there is nothing to be done in this regard. Within the single-phase installation the currents on Line and Neutral are of course equal under fault-free conditions (typically up to 100 amps for a residential installation). There's nothing you can do to reduce that. A lot of countries in mainland Europe wire up residential properties to all 3 phases (with much smaller permitted supply currents; I've seen as low as 20-amp main supply fuses), but again they go to some degree of effort to balance their phases with respect to single-phase loads. This is for grid stability reasons. For the street example again, they could have wired up every house identically, but connected the phases in a round-robin fashion, such that the socket outlet circuit(s) are on a different phase in each house, and so on. If there were ever a severe imbalance (which would be detected automatically, or by routine maintenance and inspection of distribution transformers, depending upon how bad it is), typically it would be arranged for some rebalancing work to be performed, for example by disconnecting an outgoing feeder line serving some dozen properties or more and rotating their phases (connecting the old outgoing L1 to the transformer's L2 output, L2 to L3, L3 to L1). This still maintains the phase rotation order (very important for 3-phase loads, like some EVSEs and motors) but allows a more equal distribution of loads. See https://docs.openenergymonitor.org/electricity-monitoring/ac-power-theory/3-phase-power.html https://docs.openenergymonitor.org/electricity-monitoring/ac... for why this is important. This is somewhat simplified though. Real-world loads vary their consumption dramatically, and also feature reactive components that shift the current forward or backward with respect to the voltage. A 10-amp capacitive load on L1 and L2 will not cancel out a 10-amp resistive load on L3. Harmonics are also a problem, as the article mentions.
- MisterTea 1y ago
  Well aware of how three phase systems work. You're not guaranteed perfect balance which the article addresses by stating that DC current injection is monitored and controlled which is what I was referring to.