Notes On Electricity: Generation, Transmission & Distribution

• Electrical power system consist of 4 major categories:
  a. Generation System
  b. Transmission System
  c. Distribution System
  d. Utility System
• Majority of electricity (65-70%) is produced by steam turbine plants and fuel is Coal or Nuclear.
• Hydro electric generation (25-30%) forms the 2nd largest means of generating electricity.
• Renewable sources of energy fall in a very small range (2-5%).
• Renewable sources of energy – solar, wind, ocean, bio gas, geothermal, etc.
• Gas Turbines are used during short periods of high demand for Peaking.
• Large generators voltage rating or generation is @ 13.8kV to 24kV voltage levels.
• Generator voltage is stepped up to transmission voltage level using transformers.
  Because a. Generation and Distribution stations are far away, b. There will be huge I²R losses (transmission losses or copper losses) if the voltage level is low, c. Transformers can transform this energy to higher voltage levels, without much loss.
• Transmission voltage levels in the range from 115kV to 765kV.
• Standard transmission voltages are 115kV, 138kV, 230kV, 345kV, 500kV and 765kV.
• At distribution station, the transformer steps down the voltages.
• Low voltage ranges from 34.5kV to 138kV at distribution station.
• Distribution standard voltages are 4.16kV, 12.47kV, 13.2kV, 13.8kV and 34.5kV i.e. range is from 5kV to 34.5kV.
• Why we cannot use higher voltages directly?
  a. Difficult to have equipments with such a high insulation rating.
  b. Not economical.
• Distribution transformers are used to further step down to utilization voltage levels, usually at 600V.
• Standard utilization voltages are 480Y/277V, 460V, 208Y/120V, 240V, and 120V.
• Higher utilization voltages – 6.9kV and 4.16kV are standard voltages for supplying large industrial motor loads.