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Why is there a netural in Y and not Delta loads?

2443 Views 12 Replies 11 Participants Last post by  Bird dog
I know the neutral is used for unbalance loads and to complete a circuit but, how come it's not needed on 3 Phase delta circuits (3 phase 600V Motor) is there any thing as an unbalance in 3 phase delta and if so where does the unbalance amps go?
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Define "unbalanced load" better yet forget you ever heard it. It's mostly used by people with an imperfect understanding of what's going on. I'm at work so can't go into detail but I'm sure you'll get lots of direction here. Just wanted to add my two cents that this isn't an art, it's a science and as such must have well defined terms.

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What makes you think "600V" is Delta? In most of Canada, the 600V distribution is 600Y347V.

A 3 phase motor does not use the neutral for anything, so you never give the motor more than the 3 phases, regardless of whether it is derived from a Delta or Wye service.

Inside of the motor, the windings might be Delta or Wye for various reasons, but still, that has no bearing on how you connect it to the line source, it's still just 3 phases.
 

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... is there any thing as an unbalance in 3 phase delta and if so where does the unbalance amps go?
There is such a thing as unbalance in a delta, it just takes on a different form.

If you have three hot wires supplied by a delta source, A, B, and C, then balanced operation would be when the currents and power factors are identical for all three wires.

In terms of how current flows to a normal balance load, it will normally from from A to both B and C, and so on, with the net current when you vectorially add the three line currents being zero.

An unbalanced load would take current from A, for example, and return it to B with no current on C.
There is no condition of load that can result in current only on A.
 

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Neutral creates unbalanced.

I know the neutral is used for unbalance loads and to complete a circuit but, how come it's not needed on 3 Phase delta circuits (3 phase 600V Motor) is there any thing as an unbalance in 3 phase delta and if so where does the unbalance amps go?
First the neutral is not used for unbalanced loads it creates unbalanced loading. It is for getting a reduced voltage single phase load out of a three phase system.

Using two of the three phases will also give you single phase voltage at LINE voltage.

As for as Delta it can have a neutral but it is a center tap on one phase called a high leg or wild leg system.

Hope this helps.
Cowboy
 

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Typically delta is used when the load is a balanced 3 phase load. Think of it as 3, 600v loads just in one unit ex. A motor and also a transformer. Most commonly a load is used in delta because each leg needs to be balanced.
A wye connection is when loads are not balanced. Your panel is in wye. Each phase isn't exactly balanced. We try to get it as close as possible. A neutral is the safe path back to the transformer.
When you talk about the neutral carrying the unbalanced load you talking about a 3 wire Edison circuit ex. A stove. One circuit may draw more because of the 120v clock and lights, so the difference is carried on the neutral whether to or from.
 

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Here's a few things that may be relevant. Some of these have already
been mentioned above.
-the connections indicated by a delta or wye dwg could be shown in
other ways ie all 3 windings could be parallel to each other with the lines
arranged to interconnect them into a delta or wye. Why are they never
drawn in other ways? Answer: the delta and wye are not just a connection
representation, it's also a vector diagram showing the phase angle between
the phases.
-3 phase systems are much better than single phase for powering a motor
as it easily creates a revolving magnetic field. If you've been to trade school
you might have the Delmar book. Look at figures 32-1 to 32-8 to understand
how this works.
-In Canada, the street voltage is very commonly stepped down to 600V where
it enters commercial and industrial buildings. If it's being used to power mixed
loads ie motors, lights, plugs, etc, the transformers will be set up to create
347/600 wye. From there the single phases are stepped down again as
necessary.If it's picking up motors only, then no neutral is needed and so
the transformers will be set up to create 600V delta.No neutral equals less cost.
P&L
 

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Unbalanced loads are immaterial to your type of three phase supply (Wye or delta). Unbalanced loads are typically caused by electricians connecting too much single phase load to one or two phases without measuring (or observing) the loads already in use.

An example for a WYE connection: An electrician is asked to install power for a 120volt 2kW heater (16.6amps). He checks the panelboard, see the next available space for a single-pole 20amp breaker is #6. Circuit #6 is a blue phase (or "C" phase), at least here in Alberta, and only at 250volts and below (above 250vac, it's a yellow). The electrician does not realize that the "C" phase is already drawing more AC energy from it's upstream CDP (current distribution panelboard) comparative to the other two phases. If he proceeds to connect the heater to circuit #6 (the "C" phase), he is going to compound the "imbalance load" by further adding to it. In this Wye arrangement, the ungrounded conductor ("hot") and it's neutral provide the circuit in which necessary current will flow.

An example for a DELTA connection: The electrician is asked to install power for a 208vac 2kw (9.6amps). Again, the electrician does not check the existing load on all the three phases. He proceeds to connect the heater into a two-pole 15amp breaker whose one phase is blue (or the "C" phase). Again, he has further contributed to the existing load imbalance to the "C" phase. In this three-phase arrangement, there is no neutral, the ungrounded conductors ("hot") supply energy to the load regardless of imbalance.

Imbalance in either system is produced by improperly distributing 1-phase loads from a 3-phase panelboard. Naturally, 3-phase motor loads are inherently balanced. In any case, if the load to a 3-phase panel is not balanced perfectly....it's not big deal....the worse that's gonna happen is the upstream overcurrent device (breaker or fuses) is going to open the circuit. True, that's a nuisance......but the building's not gonna burn down because of it!!!
 

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I know the neutral is used for unbalance loads and to complete a circuit but, how come it's not needed on 3 Phase delta circuits (3 phase 600V Motor) is there any thing as an unbalance in 3 phase delta and if so where does the unbalance amps go?
Here's a short but useful description of Y ∆

http://www.pumpsandsystems.com/topics/pumps/why-wye-why-delta

http://www.pumpsandsystems.com/topics/pumps/pumps/why-wye-why-delta

Fairly basic, but I find it gets the points across well


As for 'where' the unbalanced current goes, I'd like to say 'BACK TO EARTH!!' ... just because :jester:

:laughing:
 

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As for 'where' the unbalanced current goes, I'd like to say 'BACK TO EARTH!!' ... just because :jester:

:laughing:[/quote]

Seriously, it goes back to its source whether it be a transformer or generator. :thumbsup:
 
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Thinking of the unbalanced current as missing current is all wrong. All the current is present and accounted for. There may be more load on one leg than another but nothing is missing. It's not like an unbalanced equation in chemistry, it's like having more weight on one side of a boat.
 

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As for 'where' the unbalanced current goes, I'd like to say 'BACK TO EARTH!!' ... just because :jester:

:laughing:
Seriously, it goes back to its source whether it be a transformer or generator. :thumbsup:[/quote]


I know .... just stirring the pot :jester:

:laughing:
 

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emtnut,
I know you were, but, I don't want the OP to get confused when the ground rod crazies come out of the woodwork. Now where did I put the roach spray...:jester:
 
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