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.
Add them upAnswerThere is no 'total' current in a three-phase system. The current flowing in each line (not 'phase') is considered separately. And you most definitely don't 'add them up'!
Three phase or two phase? Three phase requires three large wires for the current needed
All transformers, single phase or three phase have a "no-load current" rating. That is simply the nameplate rating of the Xformer in VA, (volt-amps) or KVA (1000Volt-amps) for larger Xformers. Simply divide the nameplate rating in VA or KVA by the supply voltage and you'll get the Xformers potential maximum output in ampheres.
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.
The following equation only works for a balanced three-phase load, that is, where each of the three phases is identical in all respects:P = 1.732 VL IL x power factor, where VL and IL represent line voltage and line current, respectively.For unbalanced loads, you must determine the power of each phase, using the following equation, and add them together to find the total power:Pp = VP IP x power factor, where VPand IP represent phase voltage and phase current, respectively.
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.
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.
The XO denotes the joined secondary terminal connection of three single coils of a three phase transformer. It is the common return on any unbalanced current of a three phase system.
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.
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.
In a three-phase unbalanced star connected load supplied from a three-phase three-wire supply, Kirchhoff's current law is satisfied by ensuring that the sum of currents entering a node is equal to the sum of currents leaving the node at any point in the circuit. This principle holds true even in unbalanced conditions by accounting for the phase differences and magnitudes of currents in each phase.
As many single phase loads as is needed by the installation. The key to loading the three phase wye system is keeping the current equal in all three phases. As the neutral only carries the unbalanced current it is prudent to keep the current as low as possible by equalizing the loads on the phases.
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.
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.
There is a lot of confusion amongst consumers that an Unbalanced LoadStabilizer is generally superior to a Balanced Load Stabilizer. To clarifythis myth certain fundamental principles connected with Transformersare given below:1. Definition of Balanced and Unbalanced loads:a. A Three phase Loads on a 3 phase supply system is a Balancedload because it draws equal current from each phase. Three phaseMotors, Converters; Rectifiers using 3 phase input supply arecommon examples of Balanced loads.b. A single phase / 2 phase loads on a three phase system is calledUnbalanced load. Normally Unbalanced loads have to use aneutral wire in the system. The 2 phase loads may not require aneutral.
Add them upAnswerThere is no 'total' current in a three-phase system. The current flowing in each line (not 'phase') is considered separately. And you most definitely don't 'add them up'!
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.