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Kirchoff's Current Law states that the signed sum of the currents entering a node is zero. If the neutral point is the node, then, in a balanced system, hot matches the other two hots, resulting in no current through neutral. Any imbalance, either due to neutral to hot current flow that is not balanced by the other two neutral to hot current flows, or due to ground fault, will result in a current flow on neutral, so that the sum of zero is maintained.
When you think about this, remember that the law said "signed" and "entering". When you analyze a circuit, simply be consistent in your usage. For instance, in a balanced system, current entering the neutral node from one hot side is considered positive, and the current entering the neutral node from the other hot side is considered negative, i.e. it is leaving, not entering.
This gets more complicated in three phase power, because now you have to consider phase angle, but the concept is exactly the same...
If you are connected in wye, with a neutral, then the neutral conductor will have zero current on it only if the three phase hots have the same current on each. If you do vector analysis on this, adding up sin(x), sin(x+120), and sin(x+240), you get zero.
The same thing happens when you are delta connected, without a neutral, but then the imbalance occurs out in the distribution system, beyond the service Transformers, because the distribution system is generally a wye system.
Ground fault will, of course, "change the rules", because you no longer have only four paths to that neutral point node. In fact, that is how ground fault current interrupters (GFCI's) work - they measure outbound current and compare it to inbound current - they must be equal and opposite, i.e. they cancel each other out - otherwise there is another path - a ground fault - and the device trips.
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What is the effect of an unbalanced load of generators?
An unbalanced load prevents the generator delivering its maximum power. That is because each phase has an equal upper current limit that it can deliver, and in an unbalanced system, if one phase is delivering the rated current it follows that the others are not.
Is the line is necessary for the balanced star- connected load?
I think you probably mean is a neutral conductor necessary for a balanced star-connected load? If this is what you mean, then the answer is no, it isn't, as the phasor-sum of the phase currents will equal zero. Often, though, it is difficult to achieve a balanced load, so a neutral is then necessary, as it is needed to provide a return path for the unbalanced current -without this neutral, the phase voltages would change and become unbalanced.
What is phase current?
A phase current is the current passing through a phase, whereas a line current is the current flowing through a line.
What is the oscillating neutral in transformer?
An 'oscillating' neutral can exist when the star point of a three-phase, star (wye) connected, secondary winding becomes disconnected from earth (ground) -e.g. if copper thieves have removed the earth conductor or it simply becomes disconnected. This results in a 'floating neutral', in which the phase voltages are no longer necessarily equal to each other (in other words, the three phase voltages have become 'unbalanced') the extent to which depends upon how unbalanced the supplied load is. An 'oscillating' neutral occurs when the displacement of the neutral point changes as it responds to changes in the unbalanced load currents.
How to Calculate three phase watts with unbalanced phase current?
You will need to determine the power per phase, and add them up to give the total power of the three-phase load. To do this, you will need to multiply the phase-voltage by the phase current by the power factor -for each phase.
What is the limit or range of the neutral current in an unbalanced three phase system for it to be regarded as faulty?
The limit or range of the neutral current in an unbalanced three phase system is the third harmonic in single phase non-linear load current is the major contributor to neutral current.
What happens if neutral of three phase four wire system is break?
For a balanced three-phase load, the neutral current is zero, so the loss of the neutral would have no effect.However, for an unbalanced load, the 'difference' between the line currents results in a neutral current.So, for an unbalanced load, if no neutral current can flow, then the load's neutral point will no longer remain symmetrical, and the line voltages will become unbalanced. If the unbalance is severe, then individual loads may be subject to over-voltages or under-voltages.
What may be the maximum neutral current in unbalanced nonlinear load?
The sum of all phase conductor currents.
How do you balance the unbalanced load in 3 phase?
If the load is connected in wye (star) and it has a neutral, then the vectorial-difference of the phase currents will flow in the neutral and there will be no problem. On the other hand, if there is no neutral, then an unbalanced load would cause unbalanced phase voltages.
Can the neutral conductor be downsized in a 3 phase electrical system?
Yes, you can reduce the neutral in a three phase system. you must figure the unbalanced current the neutral will carry and also make allowances for any harmonics that may be present.
Why can the neutral wire diameter be reduced in relationship to the phase wires?
The Neutral wire should be the same gauge and size of the phase wires. Only the Earth or Equipment wire can be smaller than the phase(hot) wires. <<>> On a three phase four wire distribution system the neutral can be reduced in size. The neutral only carries the unbalanced load current and should be sized to that current. The highest current load to neutral of the three legs is used to calculate the neutral sizing. There is no reduced neutral allowed on discharge lighting and non linear loads. A demand factor of 70% shall be permitted to be applied to that portion of the unbalanced load in excess of 200 A.
Is there an advantage of having a neutral wire in an unbalanced electrical system?
A neutral wire is essential in a three-phase star (or wye) connected system supplying an unbalanced three-phase load. Without a neutral, the voltage across each of the loads may become unbalanced, too.
Effect of unbalanced load in three phase system?
Unbalance. Large amounts of unbalanced current can cause negative sequence and ground relays to operate. There are many problems that result from "too much" unbalance. Understand that no system is perfectly balanced, though. <><><> If the load is balanced there will be no current flowing in the neutral. For that reason a neutral wire is sometimes not connected to a balanced three phase load. An unbalanced load will cause neutral current to flow, if a neutral is connected. due to unbalanced load ,some current will flow through the neutral wire.hence due to I^2R losses voltage drop will occur in neutral.so the voltage regulation will decrease.
Why is the neutral wire thinner in overhead 3-phase AC transmission line?
A smaller neutral wire in a three phase system can be used because it does not carry the full line current. It carries the unbalanced current of all three leg loads. This is one reason that three phase loads on a distribution panel should be equalized as much as possible to reduce the current on the neutral.
What if the fourth wire in a three phase is having impedance would the current in the neutral line remain to have a value of zero?
When the system is in balance, with three equal phase currents, there is no current in the neutral 4th wire and it is not needed. However if the load is unbalanced, the neutral is needed to maintain the star point at zero volts.So for example a street of houses fed by a 3-phase supply needs a neutral because the houses draw unequal currents from the different phase lines, although a large enough collection of houses would tend to balance itself out.If a three-pase system has equal currents the current in the neutral is zero. If two phases draw equal current but the third has no load, there is an equal current in the neutral, and if one phase draws current but the other two have no load, there is again an equal current in the neutral.ANOTHER ANSWERA three-phase, four-wire, system comprises three line conductors and a neutral conductor. If the load supplied by this system is balanced (i.e. the loads connected between each line and neutral are identical in all respects), then no current will flow in the neutral conductor regardless of its impedance. If the load is unbalanced, then a neutral current will flow in the neutral conductor. In other words, the impedance of the neutral conductor plays no part in whether or not there is a neutral current.
Is there any current flow through the neutral wire of single phase motor?
Yes. It is identical to the line current.
What is the purpose of the neutral?
On a single phase supply the neutral is one of the current carrying wires, the other one being the live wire. The neutral is earthed at the tansformer and sometimes at other places as well depending on the system in use. On a 3-phase 4-wire system the neutral carries current only when the load is unbalanced, in other words when there are unequal currents in the three live wires.
