1.3 THE DISTRIBUTION OF ELECTRICITY THE POWER GRID What is a power grid? A is the system through which electricity from power stations reaches its final users, making it possible to have electrical energy in homes and workplaces all over the world. The work of a power grid is based on three steps: , , and . power grid power generation transmission distribution Power generation Electricity is produced in plants, called , by big generators powered by different sources . Power stations in almost every country of the world produce electricity in the form of alternating current, which is more suitable than direct current to be transmitted over long distances as its voltage is easier to increase or decrease. power stations 1 MORE All the sources of energy available at present are described in unit 1.2. 1 Transmission As power stations are usually located far from populated areas, electricity must travel long distances through cables, held by tall towers or , or placed underground . These cables oppose a certain amount of resistance to the passage of current, which causes big of energy. In order to minimise these losses, electricity has to be transmitted at high voltage . For this reason, the voltage of electricity produced in power stations is increased in , where convert electricity into high-voltage power before it is transmitted. Alternating current is easier than direct current to be stepped up or down. pylons 1 losses 2 substations step-up transformers DO In your opinion, what is the reason for choosing either method of transmission? 1 MORE Electricity is usually transmitted at 230-400 kV in Europe, 500 kV in North America and 1,000 kV in China. 2 Distribution Before electricity is delivered to homes or workplaces, its voltage must be reduced. The voltage needed varies considerably according to the user: houses normally use current at 120-240 V, depending on the country; industrial plants may require voltages from 10 to 30 kV. For this reason, , which can be found in substations or even on the poles carrying the distribution cables, lower the voltage of electricity to the suitable level for every category of user. Step-down transformers are usually found near urban areas to reduce the distance at which electricity is delivered. transformers step-down Safety along the power grid The cables transmitting high-voltage electricity over long distances are not covered with insulators. To avoid accidents from happening, cables are hung high above the ground; in this way, they are kept far away from people and vehicles. This also creates a large air gap between the cables and the ground, granting air insulation. Cables must also be insulated from the tower that holds them, which is usually made of metal. For this reason, they are connected to the towers through long insulators, usually made of ceramic discs.