No neutral on three phase

[magnoliafan89]

Hi all
Need some help remembering some college work.
Been doing a job and we are pulling in 400mm singles in parallel, got three phases and a seperate earth but no neutral.
From what i remember from college was it becuase if you had the phases all balanced youd have no current to go on a neutral so dont need one. I was trying to remember all those calculations and diagrams we did in college so i asked the bloke i was with to explain it to me so i could better understand but he said he couldn't remember either.
Is this why there is no neutral and it is as simple as the loads being balanced or was there another reason?

Thanks for any help guys hope you're all keeping busy

 

[Pete999]

Hi all
Need some help remembering some college work.
Been doing a job and we are pulling in 400mm singles in parallel, got three phases and a seperate earth but no neutral.
From what i remember from college was it becuase if you had the phases all balanced youd have no current to go on a neutral so dont need one. I was trying to remember all those calculations and diagrams we did in college so i asked the bloke i was with to explain it to me so i could better understand but he said he couldn't remember either.
Is this why there is no neutral and it is as simple as the loads being balanced or was there another reason?

Thanks for any help guys hope you're all keeping busy

What Voltage are the single operating at LV or HV and what are they feeding?
Comparison between Star and Delta Connections - Electrical Technology - https://www.electricaltechnology.org/2014/09/comparison-between-star-and-delta-connections.html

 

[Squid]

Three-phase electric power - Wikipedia - https://en.wikipedia.org/wiki/Three-phase_electric_power

 

[benji]

If its coming from lv side of transformer to feed a switchboard i would have thought it would need a neutral because the star point connection would be at the transformer winding

 

[Pete999]

If its coming from lv side of transformer to feed a switchboard i would have thought it would need a neutral because the star point connection would be at the transformer winding

That's right who's idea was it to run just the 3 phases, this doesn't have anything to do with a wind generation install does it?

 

[Lucien Nunes]

You don't need a neutral for:

a) 3-phase loads that are delta connected, regardless of whether they are balanced or not. All current is taken between the lines and there is no neutral point to connect. Line currents may be equal e.g. motors, or different e.g. machinery with a delta-star input transformer.

b) 3-phase loads that are star-connected, provided they are inherently balanced. E.g. 400V 3-phase heater battery with 230V elements, the star point will sit near neutral volts and it doesn't matter if it strays a little due to differences in resistance, so there's no need to actually connect it to supply N. Line currents will be equal.

c) Single-phase loads operating at line-line voltage. E.g. some welders, control transformers in 400V machinery. Again no neutral connection on the device as the current is taken between two lines. Often referred to as 2-phase loads (because they connect to two phases) but technically single-phase.

A machine with a mainly balanced load (e.g. 40kW of 3-phase motors, 250W of single-phase 230V computer) will often have a 400-230V stepdown transformer to supply all single-phase loads line-line to avoid the need for a neutral connection.

 

[sevuk]

Look up Delta connections, and compare it to star connections, it should jog your memory.

 

[Pete999]

That's right who's idea was it to run just the 3 phases, this doesn't have anything to do with a wind generation install does it?

A response would be nice?

 

[sevuk]

A response would be nice?

Actually, there's a point, what on earth is this for?

 

[Pete999]

Actually, there's a point, what on earth is this for?

#2

 

[magnoliafan89]

Hi guys thanks for the answers sorry i haven't replied its been a long day. They are being fed off a 11kv sub which is obviously stepped down to then feed the switch they come from and its feeding a machine the other end.
Again thanks for the responses guys

 

[LewisM]

400mm each phase that's one big ----ing machine !

 

[magnoliafan89]

400mm each phase that's one big ****ing machine !

400mm in parallel and yeh its bigger than the average bear

 

[ipf]

.What is it feeding?.... one big panel with all control necessities involved, maybe?

 

[magnoliafan89]

A machine that supposedly melts plastic.

 

[ipf]

A machine that supposedly melts plastic.

Not much known about it, then?
Some form of extruder.....may be melting plastic for remoulding purposes? You don't just melt plastics, it's for a reason.
Still, with such a supply, it'll be big....if it's specifically for that purpose.
In such cases, though, it would have to be assumed that other local machines would be involved....for remoulding, at least.

 

[Squid]

.What is it feeding?.... one big panel with all control necessities involved, maybe?

Wales.......

 

[ipf]

Wales.......

You mean whales?

 

[Squid]

You mean whales?

Nope, the fat layabouts past Bristol I believe........

 

[magnoliafan89]

Not much known about it, then?
Some form of extruder.....may be melting plastic for remoulding purposes? You don't just melt plastics, it's for a reason.
Still, with such a supply, it'll be big....if it's specifically for that purpose.
In such cases, though, it would have to be assumed that other local machines would be involved....for remoulding, at least.

Yeh an extruder. I dont know much about the machine ive just seen the plans and came up midway through the job