Question { Bhel, 17058 }

Why current flows in nutral? As per theory there should be
no current in 3 ph explain.

Answer

1. As per the theory, No current should be flowing in the neutral. But this is theoretically possible when the load in each phase are perfectly balanced. As the switching patterns of each loads in 3 phases are not exactly the same, some amount of neutral current is likely to flow through the neutral.

2.Another likely cause as to why there is current flowing in the neutral is due to the effect of harmonics. Lets take an example of transformer. The Hysteresis loss in transformer causes a non-sinusoidal exciting current to flow which mainly comprises of third and fifth harmonics. Since the line-line third harmonic voltage is zero, these current can only flow through the neutral wire or around the mesh winding.(If these harmonic current donot get a path to flow, the flux in transformer is not sinusoidal and the output voltage is non sinusoidal as well!!). Hence, high current might be flowing in neutral and there is even the provision of doubling the size of neutral wire to prevent its overheating.

Question { 5228 }

why reactive power produce in generator?
why inductive load absorbe reactive power?

Answer

Reactive power is produced by the synchronous generator basically due to the excitation current supplied to it. The VAR it can produce can be controlled by controlling the excitation current with the help of AVR.

Question { BARC, 5364 }

how can u say about the line by looking at the tower ?
{voltage rating of the line}

Answer

Just like the other people said, counting the number of insulator will give you the idea of voltage level of the line. If there are 6 insulators, it is basically 66 kV and if there are 9 insulators, its 132 kV and so. If the tower has horizontal configuration , then u can almost predict that the voltage level exceeds 200 kV. It is because horizontal towers are used for voltages exceeding 132 kV ,to reduce the height of tower.