Stepup Transformer Connections

In most cases, all the step up transformer is usually for power transmission to a long distance with high voltage so that the power transmission line conductor will be a small conductor and does not need to have a big conductor. High Voltage transmission also prevent voltage drop along the transmission line.

All the high voltage does not need to have the Neutral line. That why the step up transformer is connected as star to delta transformer. As you can observe, in your factory even for 3.3KV power supply does not have the neutral line. They come in with 3 phase only to your step down transformer.

Small power distribution are normally solidly earth. It is not necessary to have resistance or reactance earth. Only big transformer with high MVA is resistance or reactance earth. This to limit the faults current flowing into the earth if there is a fault in the line.

You can use resistance or reactance earth for small power distribution transformer but your cost of installation will be very expensive.

Why no neutral is required in High voltage lines?

Why small transformers are solidly earthed?

dear,

to save the cost of 4th neutral wire, normally transmission lines are 3 phase 3 wire. Neutral is required in local substations on consumer's side for various reasons of safety, voltage levels, etc..

delta winding requires smaller cross section of Copper, so, cost of transformers also reduces. Neutral is not at all useful in power line transmissions. What for you require neutral in these cases ?

Most high voltage does not have the neutral line as there is no equipment to associate with it. For example, a 11KV high voltage. The phase voltage to Neutral will be 6.531KV. As you can see, there is no such equipment operating at 6.531KV single phase in the market. or let say the lowest voltage of 3.3KV. For the phase voltage to neutral will be 1.905KV.

Other point, is that, the equipment for the control of the high voltage single phase will be very expensive to use and no one will manufacture it as it is not the common voltage.

That why high voltage is remain 3 phase system only without the neutral line. We have high voltage motor with 11KV (3 phase system) or Transformer with 3.3KV, 10KV, 11KV, 33KV (3 phase system).

For Low Voltage like 415, it has the neutral line to provide single phase supply for 220V. That what you have in your home to operate with it.