Consequences of no Neutral Conductor

[soldier_sss]

Good Night Everyone.

Question ?

I have a 12kV : 440/240 Y : 1.5MVA Transformer and a 3w conductor connected between supply and load (armoring included)

The Load is an Asphalt Plant that uses app. 345kVA @ 440V, 3p.

I am concerned with the fact that if the Load is unbalanced, then how does the system compensate for the return current since the

conductor is 3w with no neutral.

Thanks for your assistance.

 

[GoldDigger]

Good Night Everyone.

Question ?

I have a 12kV : 440/240 Y : 1.5MVA Transformer and a 3w conductor connected between supply and load (armoring included)

The Load is an Asphalt Plant that uses app. 345kVA @ 440V, 3p.

I am concerned with the fact that if the Load is unbalanced, then how does the system compensate for the return current since the

conductor is 3w with no neutral.

Thanks for your assistance.

1. 440Y/220 does not exist unless you are talking about a high leg delta and that has to be four wires, not three.
2. If all of the loads are three phase and there are no fault paths to ground the only possible imbalance will involve different currents in each hot wire with the vector sum still being zero. You cannot have line to neutral current without a neutral.
3. Is this grounded? If so how? If ungrounded, even a single fault cannot produce current outside the three wire set.

 

[soldier_sss]

1. 440Y/220 does not exist unless you are talking about a high leg delta and that has to be four wires, not three.
2. If all of the loads are three phase and there are no fault paths to ground the only possible imbalance will involve different currents in each hot wire with the vector sum still being zero. You cannot have line to neutral current without a neutral.
3. Is this grounded? If so how? If ungrounded, even a single fault cannot produce current outside the three wire set.

Noted:

1. The transformer is actually a 416/240 Y.
2. The load is primarily 3p.
3. The ground connection is through the armoring only.

 

[GoldDigger]

Noted:

1. The transformer is actually a 416/240 Y.
2. The load is primarily 3p.
3. The ground connection is through the armoring only.

The EGC connection through armoring only is probably fine. But is the center point of the transformer's wye secondary connected to ground? Or left floating?

You are not allowed to have any line to neutral (or line to ground loads) with this setup. If you need to feed 240 to anything you will need to add a transformer whose primary is line to line on the 416.
If all loads are line to line there is no way to produce any net imbalance. What goes in must come out and vice versa.

 

[Tony S]

I_n = SqRt(I_a²+I_b²+I_c²)-((I_a*I_b)+(I_a*I_c)+(I_b*I_c))

If a neutral ground jumper is fitted at the plant I_n is carried by the cable armourings. Not a good situation to be in.

 

[Sahib]

If your plant uses only 3 phase motor loads, no problem.

 

[Besoeker]

I_n = SqRt(I_a²+I_b²+I_c²)-((I_a*I_b)+(I_a*I_c)+(I_b*I_c))

Surely irrelevant if there is no neutral conductor?

 

[Besoeker]

If your plant uses only 3 phase motor loads, no problem.

I would still earth the transformrt star point to prevent the voltages floating to an indeterminate level wrt earth.

 

[Sahib]

I would still earth the transformrt star point

That would be silly, if the power supply is of ungrounded type.

 

[ggunn]

Good Night Everyone.

Question ?

I have a 12kV : 440/240 Y : 1.5MVA Transformer and a 3w conductor connected between supply and load (armoring included)

The Load is an Asphalt Plant that uses app. 345kVA @ 440V, 3p.

I am concerned with the fact that if the Load is unbalanced, then how does the system compensate for the return current since the

conductor is 3w with no neutral.

Thanks for your assistance.

The rest of the scenario notwithstanding, with two CCCs and no neutral there can be no unbalanced current because there are no line to neutral loads. Every circuit is a loop and the current in every part of a loop is the same.

 

[Besoeker]

That would be silly, if the power supply is of ungrounded type.

Why exactly??

 

[Tony S]

Surely irrelevant if there is no neutral conductor?

True, but the fault current still stands

That would be silly, if the power supply is of ungrounded type.

Why would a machine tool be ungrounded?

 

[Sahib]

Why exactly??

Consider this scenario:

A plant with ungrounded power supply design for greater reliability is operating smoothly.

Someone enters the plant and proposes

I would earth the supply transformer star point to prevent the voltages floating to an indeterminate level wrt earth.

Does not that appear silly?

Why would a machine tool be ungrounded?

A machine tool in an ungrounded power supply system still needs to be grounded.

 

[Besoeker]

Consider this scenario:

A plant with ungrounded power supply design for greater reliability is operating smoothly.

Someone enters the plant and proposes



Does not that appear silly?

Leaving it to float to any voltage isn't just silly. It is potentially dangerous.
That's an avoidable risk and I would avoid it. So should you.

 

[Sahib]

Leaving it to float to any voltage isn't just silly. It is potentially dangerous.
That's an avoidable risk and I would avoid it. So should you.

The code permits ungrounded power supply systems.

 

[Besoeker]

The code permits ungrounded power supply systems.

Just because you can doesn't mean you should.

 

[Sahib]

Just because you can doesn't mean you should.

It is not a case of 'Just because you can doesn't mean you should'.

It is a case of 'It does' as it is an industrial practice allowed by the code.

 

[Besoeker]

It is not a case of 'Just because you can doesn't mean you should'.

It is a case of 'It does' as it is an industrial practice allowed by the code.

For me, safety should be the overriding concern regardless of you may be permitted to get away with.

 

[Sahib]

It is not a case of 'Just because you can doesn't mean you should'.

It is a case of 'It does' as it is an industrial practice allowed by the code.

For me, safety should be the overriding concern regardless of you may be permitted to get away with.

The code is primarily concerned with safety and it allows it!

 

[iwire]

The code is primarily concerned with safety and it allows it!

Yes, that has been firmly established.

What is also a fact is that the code is a minimum design standard and most of us exceed it on a regular basis.