why three phase system taken in HV power transmission line?

It takes three phase, three wire system on high voltage AC transmission line system in our country, that’s the main reason for name of three wire. And the DC transmission line take two phase system, that’s why its named two wire.

Phase degree difference is 120C when the three phase wire pulled from transformer, which is convenient to push three phase motor rotation, moreover, it could supply power in three lines.

It is sure null line must be required in the lighting circuit,the null line will be got at the user side when voltage drop and install in star connection, that’s, when three phase cable connected with three phase electric transformer heading, the wire will be connected by each ending, which is formed the null line.

Three phase A.C cable, A color in yellow, B color in green, and C color in red. The neutral wire if no connected by earth in purple, if connected in black.

In D.C. circuit, the positive pole will be in brown, and the negative will be in blue.

Now our HV power voltage system takes voltage level 10KV, 110KV, 220KV, 500KV,1000KV,no null line is required. For these HV voltage system can not be allowed to connected with electric equipment. That’s the main reason why three phase wire system in HV power transmission line.