Generating Stations

it need not be 11kv always, in US they generate 13.8 kv, its all depends upon alternator design.

is it related to form factor?

No. It's a relationship between the primary and secondary windings in transformers, specifically the number of turns.

That's a pretty vague question.

1. As to why that specific value, design standards have been developed to enable equipment from one manufacturer to work with equipment from another manufacturer. There are standards for nearly everything. The only way you know the length of a meter is that there is an agreed standard size. In the E.U., and most non-USA locations, 11 KV is one of the standard voltage levels for both generation and distribution. In the USA, 13.2 KV is a standard for distribution, and 13.8 KV is a similar standard for generation.

2. Regarding why generation voltage is so much higher than that used by the customer, it is a primarily an economic decision. If you are using a small generator to provide standby power at your home or business, it makes sense to produce the power at the same voltage it is used. You avoid the cost of a transformer, and the amount of power being generated is small enough that power losses are not a concern. That is not the case with bulk electricity. Commercial generators produce hundreds or thousands of times more power than a private standby unit. Generating stations are usually tens or hundreds of kilometers away from their customers. The electric industry is a business, even when that business is owned by the government, and economic factors will prevail in the design of the equipment.

Bulk power is generated, transmitted and distributed at the highest economical voltage, in order to reduce the associated current. The physical limit on electrical equipment is heat generation due to the current flowing through the windings. This affects the design of every electrical component, from the smallest IC chip to the largest generator. An additional consideration is that the producing that heat uses real power (watts). The power creating that heat cannot be sold for profit, but it has a real cost to the producer in terms of fuel, maintenance, etc., and must be considered a loss of revenue.

Mathematically, power = voltage x current (KW = I x E). Ohm's Law states that voltage = current x impedance (E = I x R). Replace voltage in the power equation, and you see that power = current x current x impedance (KW = I² x R). (Reactive power considerations are omitted for simplicity, but the concept does not change when power factor is considered.) In practical terms, the first equation shows that doubling the voltage means you can make or transmit the same amount of power with half the current. The last equation shows that halving the current reduces losses to 1/4 of the original value.This has a huge impact on the design of generators, transformers, and transmission lines.

There is a voltage point where the cost of the insulating system outweighs the benefits of lower losses. As insulation systems have improved, that economic decision point has moved toward higher voltages. The first units I worked on generated at 480V. Twenty years ago we demolished several 6.6 KV units to make room for new 13.8 KV units. Today, many recently installed units generate at 34.5 KV (USA) and 33 KV (non-USA). It would not surprise me to see 66 KV and 69 KV generators in the next 25 years.

well, its good explanation, in India the generation and transmission voltage level are 3.3kv, 6.6kv, 11kv, 22kv, 33kv etc. the level is either fraction of 11 or multiply of 11, is it due to the equipments are design in that way or is there certain advantage?