Higher Neutral Current

What were the formulas you used. The answer depends on the phase angle of the current and voltage.

You didn't mention which formula you used. If there is any formula exists for the calculation of neutral current using the magnitudes of line currents, the formula must have sort of some assumptions such as the loads are resistive or all loads are of a certain power factor. In case, the assumptions are not valid for the loads, the formula doesn't bring the correct result. As wareagle indicated, the neutral current can be calculated using the vector sum of the line currents and in this case, you need to know both the magnitudes and angle (obtainable from load power factor) of the line currents.

- MS

How come the neutral current is so high,as far as i know that for 3 phase system with balanced load the neutral current must be zero ?

quote "How come the neutral current is so high,as far as i know that for 3 phase system with balanced load the neutral current must be zero ?"

If it were balanced all of the phase reading would be the same. Obviously it is not balanced.

Thanks for your good answer,but why in the 4 wire cable the neutral wire is always with less diameter, i can see from this situation that neutral wire has more current than phase currents ?

Quote OP "I1=5.8, I2=70.8, I3=46.6 and In=30"

Quote Guest " i can see from this situation that neutral wire has more current than phase currents ?"

As you can see the the neutral does not carry more that the phase currents. The max neutral current would occur when 2 of the phases have no load. The neutral current then would equal to the loaded phase current. If this would happen and the neutral was too small, the neutral might be damaged. Some engineers spec a neutral the same size as the phase conductors. It has to be someones responsibility to see that the phase currents are balanced as close as possible. In the OP case, he needs to shift load from phase 2(70 amps) to phase 1(5.8 Amps). If he were to move about 30 amps to phase 1, the currents would be P1 35.8amps, P2 40.8 and P3 30 amps. Fairly close to being balanced.