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Can someone explain to me please how a substation converts high voltage three wire to low voltage 4 wire?
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im looking at star-detla now but im just stuck on this today for some reasonThink about how transformer windings are connected.
There are three types of connection Delta, Star and zigzag
Doing a sketch will help you work it out.
sorry thats what i meanttry delta-star
exactly. with delta ther is no neutral butonce converted to star via the transformer ( as the psecondary is connected as star) the star point is your neutral.so the 3 wires coming in would be the higher voltage on the delta then would go through a transformer and come out as "star" providing an extra 4th wire (the neutral) ?
exactly. with delta ther is no neutral butonce converted to star via the transformer ( as the psecondary is connected as star) the star point is your neutral.
Would the star balance the load because of the neutral causing there to be a balanced load that the delta could take the ?yes, the teory is too complex for a forum post, but basically. if the loads on all 3 phases are exactly balanced (equal), the the neutral current is zero. there is a formula for unbalanced loads.
N current = Square root of /(L1^2 + L2^2 + L3^2) - (L1*L2 + L1*L3 + L2*L3
no. the balabce of the load on the star supply is determined by what loads are connected. you could have 110A on L1, 70A on L2, and 30A on L3. that would be unbalanced, and there would be current in
Ahh yes Iv seen that on a diagram where you connect the phases using the N and have them all measured accordingly, I take it delta would only be used for distribution and we would transform to a star for buildings and such, because of the unbalanced loads we would be most certain to pull?no. the balabce of the load on the star supply is determined by what loads are connected. you could have 110A on L1, 70A on L2, and 30A on L3. that would be unbalanced, and there would be current in the neutral accordingly.
this is brilliant thankyou, very comprehensive, the second part you posted I had no idea about.No, it's nothing to do with balance.
We use delta for transmission because line plant is expensive and the lowest number of wires wins. For a 3-phase system that's 3 wires.
In theory we could use 3-wire delta for distribution to individual installations and some systems work like that, without a neutral at all. Each single-phase circuit is connected between two of the three lines. E.g. one load is connected between L1 and L2, another is connected L2 to L3 etc. There's no need for the loads to be balanced, if they are unbalanced the three line currents are simply different. Shipboard domestic power is often delta, historically it was popular in parts of Europe.
But for consumers, 3-phase 3-wire delta has drawbacks. Everything has to be double-pole switched and fused because both wires of a single-phase circuit are lines. More importantly, it misses out on an important advantage of 3-phase 4-wire which is that you can take power at one voltage L-N and a different voltage L-L according to application. E.g. with 3-phase 4-wire one supply can provide 230V single-phase power with the convenience and safety of an earthed neutral, and at the same time 400V 3-phase for industrial loads with the advantage of reducing the current by sqrt(3) saving on copper and losses. These advantages of the 3-phase 4-wire system come at the cost of providing four wires instead of three, and for installations of buildings that extra cost is well justified.
So we have standardised (at least in the UK and many countries) on 3-phase 3-wire for transmission on grounds of economy, and 3-phase 4-wire for distribution to normal consumers on grounds of flexibility. Hence, most local substation transformers are wound delta-star.
That is very similar to the most common UK setup for final distribution transformers with a 3-wire 11kV delta-wound primary, and a nominal 400V/230V star-wound secondary with neutral.In Russia, there are three wires in front of the transformer on the 10 kV side, there is no neutral. There is a neutral after the transformer on the 0.4 kV side.
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