# 3 phase 4 wire system

Dear all.

I have most common question here. I have system 3 phase 4 wire system. Assume i have connected Rphase/Yphase /B phase neutral wire connected separated with 230VAC supply.
VL = √3 VPH for Line to line calculation
and if i measure line to neutral it should show 230VAC

Suppose i have connected in this setup. RPhase/Bphase/Y phase are shorted and single Rphase voltage is given. In this case what should be line to neutral voltage should be read and line to line neutral voltage should be read.

SInce phase shift no more 120 degree

In an ideal system (each phase is perfect) connecting the 3 phases together sums the 3 line voltages to zero relative to the neutral. In practice, shorting the 3 phases could result in large circulating currents since the 3 phases will not be exactly 120 deg appart and the voltages will not all be the same so the voltage vector sum will not be zero.

Hi,

Suppose i have connected in this setup. RPhase/Bphase/Y phase are shorted and single Rphase voltage is given. In this case what should be line to neutral voltage should be read and line to line neutral voltage should be read.

What do you mean. R, B and Y phase are shorted?
Is this the 3 phase supply?
If so then you have exactly that a SHORT CIRCUIT, and an OVERLOAD situation.

Is this a school/education institution problem, or is it for a commercial project?

Tom..

Is this the 3 phase supply? If so then you have exactly that a SHORT CIRCUIT, and an OVERLOAD situation. Ideally the sum of the three phase voltages is zero so shorting them together would not cause an overload.

Learn something new every day! What will the sum of the currents be?

skyvan:

Is this the 3 phase supply?
If so then you have exactly that a SHORT CIRCUIT, and an OVERLOAD situation.

Ideally the sum of the three phase voltages is zero so shorting them together would not cause an overload.

Lets see you do it in REAL LIFE!!!

Tom… :o :o :o :o :o

Hi,

[soapbox]
When phase 1 is at zero, phase 2 is at -0.86, phase 3 is at +0.86.
What will happen when phase 2 is connected to phase 3?
That is a potential difference of 1.72, NOT ZERO.
Phase 1 to phase 2 = difference of -0.86 NOT ZERO.
Phase 1 to phase 3 = difference of 0.86 NOT ZERO.
These differences mean that current will flow, lots and lots of current in the theoretical and real world when you short them together.
That is when you load them up with ZERO OHMS.
Mr Ohms Law..
[soapbox/]

Mr Thevenin, Mr Norton and Mr Kirchhoff might have something to say too.

Tom...

JCA34F:
Learn something new every day! What will the sum of the currents be?

I have just decided that I am an idiot! Curent will most definitely not be zero. Please ignore my responses.

You could try this...
(Watch the ammeters on the back wall)

PerryBebbington:
You could try this...
(Watch the ammeters on the back wall)

I want one.....

Just a 3 phase transformer with, I think, an 11kV output and some copper pipe. Shame you are not in the UK, Gaussfest is every year, well, not 2020 obviously, but apart from corona virus restrictions it is.

Ideally one would have into a Delta L1,L2,L3, and Gnd (E) to output a Y of L1,L2,L3,N,E Where the N is created by the Y connection. And depending on the situation Y and E can be connected at the D:Y xfmer.

That only 4 wires are being given it could be dangerous assuming that the 4 wires are L1,L2,L3,N when the wiring scheme could be L1,L2,L3,E. It would be best, in such a case when the 4th wire is an unknown to look at the electrical blueprints.

PerryBebbington:
Just a 3 phase transformer with, I think, an 11kV output and some copper pipe. Shame you are not in the UK, Gaussfest is every year, well, not 2020 obviously, but apart from corona virus restrictions it is.

Is that when they stoke up the power stations and turn off Jodrell Bank.

Something like that!