Neutral Voltage Shift 1e1u1v

I'm pretty sure that your phase-neutral voltages aren't wandering around; and you wouldn't know since you're looking at phase-ground voltages. The neutral-ground voltage is wandering around and has no real meaning. Very minor imbalances can move the neutral around relative to ground without meaning anything. All you have to "hold" the neutral-ground voltage in place is the parasitic capacitance between the phases and ground; switch a bit of the system in or out and you can change those capacitances. Mostly just ignore the phase-ground voltages as long as none of the phases are solidly at zero volts to ground.

Voltage of the neutral of the power source is always zero, or very close to zero (compared to the true earth), (and that is the case for the earth conductor if the earthing is properly done) .. Then for a three phase balanced load each line to neutral voltage is say 240 V and the angle difference is 120 between each phase and the other. In this case voltage of the load neutral (star point) will be same as that of the source neutral. But if the transmission or the distribution lines are not balanced, or if the load is not balanced, then the line to neutral voltages at the load terminal will not be equal in magnitude nor phase angle difference. This will make phases currents different and cause different voltage drops in the load phases. In this case, the neutral voltage will shift from the supply neutral voltage to another value. The amount of shifting depends on the amount of unbalance. Simply we can say: The neutral shift is the deviation of the potential of the load’s neutral point in respect to system neutral, which ideally, should be very close to zero volts in respect to true earth ground potential.

Voltage unbalance (in phase, or magnitude(amplitude) occurs only, if neutral is isolated or, not solidly grounded(neutral to ground voltage exist). Neutral point will be shifted(not remains at ground(zero) potential),and heavily load phase voltage, will reduce and lightly load, phase voltage will increased, which may damage the appliances connected. With unbalance load(current) there must be a path, for neural current to flow,as required, or will create,voltage unbalance. See reply," advantage of three phase four wire system, over three phase three wire system."

Force can be represented, as vector with magnitude and direction. If three forces, of same magnitude and 120 degree apart. acting on a point can shift the point? Answer is,' No'(resultant force on point is zero). Similarly voltage supplied in three phase system are 230 or 110Volts in magnitude, and are apart by 120 degree, and the common reference point at zero potential is called neutral, and if it connected to ground no current will flow from neutral to ground as there is no potential difference, as ground too, at zero potential, or we can say that, neutral is not shifted from ground. These three phase supply are received, from the mains by three phase four wire system(R,Y,B and N).

When voltage applied to load(connected between phase and neutral), current starts flowing from, phase to neutral. The current magnitude depends on size(watts) of load and phase shift on power factor(capacitive/inductive).If loads(current) on all three phases are balanced, in magnitude and phase difference of individual phase, no resultant current would be flowing from neutral to ground(or neutral is connection with ground will not make any difference, even if not connected.)as both at zero potential. If loads on all three phases are not balanced, the resultant current will flow from neutral to ground(neutral will remain at same potential as ground)and the applied balanced voltage will not disturbed. If neutral is not connected to ground, think what would happened? Answer is,' Neutral point will shifted'. How much? Scale of voltage drop produced by resultant current(not allowed to flow). Or shifting of neutral would be such that the, heavily load phase voltage will reduce and lightly phase voltage will increased. Which can be understand by drawing exact current diagram(when neutral is connected) measurements of R,Y,B and N currents. Voltage diagram, by measuring disturbed voltage, when neutral is disconnected from ground.(voltages, RtoN,YtoN,BtoN and NtoG) and comparing with scale, both drawn, current and voltage diagrams.

Mr. Hamid, unbalance is caused by the load. Neutral point in a Star Winding is the reference point where the voltage is zero or balanced from 3-phases. To eliminate the problem of Neutral shift (or Floating Neutral Condition), arching grounds due to any problems/faults in the system, the Neutral Grounding is adopted in electrical systems. Just draw yourself a simple diagram for a Star wound source feeding a 3ph load - both for an Earthed & Unearthed star points of source. Do this for both balanced & unbalanced loads separately. In all the above, no change in circuit values. Calculate currents drawn by the different loads in earthed system, apply same current in unearthed system and calculate back the voltage drops across the each limb of source winding /load. You will find the difference yourself. If your system's star point is not earthed, to keep the system in balanced condition, during any imbalances in the loads or during any fault, the neutral will get shifted.

if the unbalance load exist in the system in that case some voltage is developed at the neutral point beacuse the current at the neutral point is zero( in case of 3-phase system) if neutral is not earthed, the magnitude of the voltage developed at the neutral depend upon the unbalance load it might be produced in order of KV.