power system (transmission and distribution)

1. Electricity produces in generator plant of power company.

2. Then, it steps up the voltage and feeds into transmission network (power transmission).

3. Then, it steps down to 11KV and feeds into distribution network (power distribution) and it further steps down to low voltage (for most users like household, except bulk users such as MTR, Water Authority, etc.) for electricity supply.



You may see from the figure of the following web page:
http://www.iitk.ac.in/infocell/Archive/dirmar1/power_distribution.html

But, in Hong Kong, we use 380V 3-phase (NOT 415V) and 220V 1-phase (NOT 240V).


In other words, you may say that power transmission nears the generating side with higher voltage and power distribution nears the customers side with lower voltage.

Generation = 發電 （25KV 以下）
Transmission = 輸送 （33KV ~ 500KV）
Distribution = 分配 （33KV 以下）
Supply = 供應 （11KV 以下）

2008-05-07 09:59:39 補充：
有D小型發電廠（水力及風力發電廠）係11KV 甚至 400V 發電，然後升壓到 33KV 以上方便輸送（爲了減少輸送時電壓降），之後再降壓分配（因爲 33KV 以上好多控制繼電器如 HO4 SOKOR 'R' OLTC 等 ），而且 33KV 以上既用戶唔多，雖然 132KV ~ 275KV 用戶都有，不過好少，需要特別安排。

輸送係一個環路系統，分配係另一個環路系統，以減少用戶間既干擾。