World's Largest Hydroelectric Power Plant

Introduction

 The Three Gorges Project (TGP) is a vitally important and backbone project in the development and harnessing of the Yangtze River (Changjiang River ). The dam site is situated at Sandouping of yichang City, Hubei Province, about 40 km upstream from the existing Gezhouba Project.

Three Georges Dam is the world's largest hydroelectric dam on the basis of installed power generation capacity. It is as wide as the Golden Gate Bridge and twice as tall. The installed generation capacity is 22,500 MW. Total 34 generators are available for generating this much energy. Out of 34 are of capacity 700 MW and two are 50 MW.    Annual generation is around 100,000 Giga watt hour. The rated power is 778 mega volt ampere, with a maximum of 840 mega volt ampere with power factor of 0.9.

The main generators weigh about 6,000 tonnes each and are designed to produce more than 700 MW of power. The designed head of the generator is 80.6 meters (264 ft). The flow rate varies between 600–950 cubic metres per second (21,000–34,000 cu ft/s) depending on the head available. The greater the head, the less water needed to reach full power.

The generator produces electrical power at 20  kV. The outer diameter of the generator stator is 21.4/20.9 m. The inner diameter is 18.5/18.8 m. The stator, the biggest of its kind, is 3.1/3 m in height. Bearing load is 5050/5500 tonnes. Average efficiency is over 94%, and reaches 96.5%.

The generators are manufactured by two joint ventures. One of them includes Alstom, ABB Group, Kvaerner, and the Chinese company Haerbin Motor. The other includes Voith, General Electric, Siemens (abbreviated as VGS), and the Chinese company Oriental Motor. 

Most of the generators are water-cooled. Some newer ones are air-cooled, which are simpler in design and manufacture and are easier to maintain.

Layout and Structure

Made of concrete, the dam is 2,335 m (7,661 ft) long, and the level of the dam top is 185 metres (607 ft) above sea level. The project used 27.2 million cubic metres (35.6×106 cu yd) of concrete (mainly for the dam wall), 463,000 tonnes of steel (enough to build 63 Eiffel Towers) and moved about 102.6 million cubic meters (134.2×106 cu yd) of earth.The concrete dam wall is 181 meters (594 ft) high above the rock basis.

When the water level is at its maximum of 175 metres (574 ft) above sea level (110 metres (361 ft) higher than the river level downstream), the dam reservoir is on average about 660 kilometres (410 mi) in length and 1.12 kilometres (3,700 ft) in width. It contains 39.3 km3 (31,900,000 acre·ft) of water and has a total surface area of 1,045 square kilometres (403 sq mi). On completion, the reservoir flooded a total area of 632 square kilometres (244 sq mi) of land, compared to the 1,350 square kilometres (520 sq mi) of reservoir created by the Itaipu Dam.

Turbine

This power plant uses Francis turbines, the turbine diameter is 9.7/10.4 m (VGS design/Alstom's design) and rotation speed is 75 revolutions per minute.

Added Benefits

As well as producing electricity, the dam increases the Yangtze River's shipping capacity, and reduces the potential for floods downstream by providing flood storage space. Dam is the largest water conservancy project ever built in China, and so in the world. With the normal pool level (NPL) at 175 m, the total storage capacity of the reservoir is 39.3 billion m^3.

Side effects

The dam flooded archaeological and cultural sites and displaced around 1.3 million people, and is causing significant ecological changes, including an increased risk of landslides.