GENERATING STATION

      Basically this is a transformation at this station of one kind of energy (coal, gas, waterpower, nuclear energy, wind, solar energy, etc.) into electrical energy, often via steam. While the electricity fed into the grid is Alternating Current (AC), some of these sources of energy are used to charge batteries; all batteries supply only Direct Current (DC). Converters and inverters are available to change DC into AC, and rectifiers change AC into DC. Many industrial firms, also hospitals and other emergency operations have their own emergency generators that automatically switch themselves into the circuits if the normal electricity supply fails. These emergency generators usually are powered from petroleum based fuels. Also most cars include a small generator, called an alternator that charges the car's battery and provides electrical power to the vehicle while the engine is running. The battery is disconnected from the generator while the engine is not running, or if otherwise the generated voltage is too low, such as, for example, when there is a breakage of the fan belt.
      In order to get a lot of energy into the power grid, a lot of energy is needed to drive the generators, and in case there is a disconnection of the generator from its load the input energy must be removed immediately, or else the generator would speed up more and more, and a lot of destruction would be the result.
      To restore small generators to service they could be started up as motors, with the normal energy source supplying no energy at all at first, but then that energy is added slowly back to driving the generator normally. While power at the beginning is taken from the grid into the generator (actually it is a motor at that time), with the power flow then in the negative direction, the direction of power flow soon is reversed to normal. No synchronization is needed in that case.
       In restoring large power generators a major problem could be the time taken for the heat source to reach normality. This can take days in case of plants. In the meantime severe restrictions on electricity availability must be expected. That is why many firms have their own generators that are switched on automatically if there is a power failure.