How is energy lost from power stations?

Answer 1

A generator at a power station might produce electricity with a voltage of 25,000V and a current of 8,000A. Such a large current would cause the cables of the National Grid to get hot because of the heating effect of current. Energy would then be lost as heat to the atmosphere and by the time that the electricity had traveled from the power station through the cables to the towns and factories, much of the original energy would be lost. To reduce the energy loss, a step up transformer at the power station is used to raise the voltage to 400,000V. This is 16 times the input voltage of 25,000V.The Energy Supply Chain Much of the energy content of the available energy sources is wasted by inefficiencies the energy conversion and distribution processes. Considering domestic electric lighting as a typical example, less than 1% of the energy consumed to provide the electricity is ultimately converted into light energy. The other 99% is wasted in the supply chain. Using conventional fossil fuelled generating plant, losses accumulate as follows: 10% of the energy content of the fuel is lost in combustion and only 90% of the calorific content is transferred to the steam. The steam turbine efficiency in converting the energy content of the steam into mechanical energy is limited to about 40%. (Carnot's Efficiency Law) The rotary electrical generator is very efficient by comparison.The conversion efficiency of a large machine can be as high as 98% or 99%. Transmission of the electrical energy over the distribution grid between the power station and the consumer results in a distribution loss of 10% mainly due to the resistance of the electrical cables. Further energy is lost due to the energy conversion efficiency of the end user's appliance. Incandescent lighting is particularly inefficient converting only 2% of the electrical energy into light. The losses are considered in more detail below. Generating Efficiency Electric power plant efficiency η is defined as the ratio between the useful electricity output from the generating unit, in a specific time, and the energy value of the energy source supplied to the unit in the same time period. For electricity generation based on steam turbines 65% of all prime energy is wasted as heat. The maximum theoretical energy efficiency is defined in more detail by the Rankine cycle. For modern practical systems this is about 40% but less for older generating plant. The efficiency falls still further if fuels with lower energy content such as biomass are used to supply the plant. Efficiency Comparisons