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The neutral current in a three-phase, four-wire, a.c. unbalanced load is the phasor-sum (vector-sum) of the three phase currents. That's more-easily said than done, as the maths can be quite difficult -certainly too difficult to explain in WikiAnswers, so you should refer to a textbook which covers the topic. Probably the best approach is to use the 'a-operator', the equivalent of the 'j-operator' used for single-phase loads.
Wiki User
∙ 11y ago
Wiki User
∙ 11y agoIt is a symptom of an unbalanced load, which is probably not serious but indicates possibly inefficient power transmission. It could also indicate a fault in a load that is supposed to be balanced.
Wiki User
∙ 10y agoA demand factor of 70% shall be permitted to be applied to that portion of the unbalanced load in excess of 200 A. The only stipulation is that there can be no connected electrical discharge lighting and no non-linear loads supplied from a 3-phase, 4-wire system
Wiki User
∙ 9y agoFor a three-phase, four-wire, system the neutral current is the phasor (vector) sum of the three line currents.
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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.
How much current will flow in neutral line for three phase supply 100amps?
If all three legs of the system are balanced then zero amps will flow all the way up to 100 amps if only one leg of the three phase system is used. The neutral in a wye three phase system carries only the unbalanced current. This is why in services for a three phase four wire system you are allowed to reduce the size of the neutral conductor.
What cause current on the neutral line in a three phase?
Current on neutral in a multi phase system is caused by imbalance between the phases. Question: Are you talking about neutral or ground? The two are very different. Although neutral is grounded, it is expected to be a current carrying conductor, so current on neutral is normal, so to speak. Ground, on the other hand is a protective circuit that is not supposed to have any current on it at all.
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.
What is the formula to get neutral current in three phase transformer where three phase cureent are given?
Neutral current is the vector sum of the phase currents. You should be able to add up the phase currents from their polar quantities.
Why the neutral cable takes high current than the phase lines in three phase installation?
In a properly balanced three phase system, there is negligible current on neutral. If there is substantial current on neutral, then the system is not balanced and/or something is wrong.
Why neutral cross section is half the phase in three phase cable while it has to carry current of summation of all phase..?
The current carried by the neutral of a three phase four wire system is the un balanced current. If the three phase system was completely balanced on all three phases there would be no need for a neutral, eg a three phase motor. This neutral current will be less that the phase current so a reduction in the neutral size is allowed.
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 would be the effect on the neutral bar of a 3 phase D B if the main incoming neutral is lost?
A three phase delta system does not use a neutral in its operation.
What is line phase neutral?
Line, phase, neutral are terms used to describe the conductors in a three-phase system. The three live wires are called 'lines', and less correctly, 'phases'. Neutral is used for the fourth wire which in a balanced system carries no current.
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.
How much current will flow in neutral line for three phase supply 100amps?
If all three legs of the system are balanced then zero amps will flow all the way up to 100 amps if only one leg of the three phase system is used. The neutral in a wye three phase system carries only the unbalanced current. This is why in services for a three phase four wire system you are allowed to reduce the size of the neutral conductor.
Why set an overload relay to full load current divide by root three in a star delta starter?
In a Wye/star system the overloads look at the phase to neutral/ground current; not phase to phase current. Which is always calculated as root three or 1.73205.............etc. Therefore the overloads have to be set to the phase to neutral/ground current.
How do you reduce neutral to earth voltage in three phase system?
It is done by connecting the neutral to earth at the transformer that produces the three-phase supply. If the three phase wire supply equal currents, there is no current in the neutral wire and its whole length stays at earth potential, but if there is current in the neutral it produces a small voltage on the neutral at places away from the transformer.
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 cause current on the neutral line in a three phase?
Current on neutral in a multi phase system is caused by imbalance between the phases. Question: Are you talking about neutral or ground? The two are very different. Although neutral is grounded, it is expected to be a current carrying conductor, so current on neutral is normal, so to speak. Ground, on the other hand is a protective circuit that is not supposed to have any current on it at all.
What is the function of neutralization?
A CT is a current transformer, used to measure current flow in a conductor. Neutral is power return, usually grounded at the distribution panel. A neutral CT, then, is a device that measures the current flow in the neutral conductor. In a three phase star system, each phase returns current to neutral, but the three phases cancel each other out, resulting in effectively zero current in neutral. The neutral CT is used to detect an imbalance in the system, perhaps caused by a ground fault or by some failure in one of the phase loads. In a single phase, single ended system, there is current on neutral, so the value of a neutral CT is not so great. If you also had a hot CT, you could compare and detect imbalance between hot and neutral, which would be an indication of a ground fault. (Actually, a ground fault current interrupting device, also called a GFCI, usually compares current in hot and neutral simultaneously, because both conductors are wound together as the sensing transformer primary - any perceived current is a ground fault.) In a single phase, double ended system, such as the 120/240 split phase system used in the US, a current CT could indicate ground fault or a system imbalance but, usually, imbalance might be a normal situation as various loads are turned on and off.
