Power engineering

The Electric Power Engineering is a discipline within the electrical engineering and power engineering, the (colloquial Electric current or electricity) is engaged in power generation, conversion, storage, transport and forwarding in electrical networks and use of electrical energy. The differentiation from other areas of electrical engineering is given by the fact that they are working in energy technology usually associated with high voltage in order to very large capacities (kilo - up gigawatts ) to transfer large.

  • 5.1 Conductor cross section
  • 5.2 amperage
  • 5.3 loss

Energy supply

Much of our daily available energy is supplied as electrical energy in power plants. Different types of energy sources (eg, uranium, coal, gas, hydro, wind or solar ) will be converted into useful energy (such as light, heat, cold). The demand for energy in a public power system is strongly influenced by seasonal fluctuations. In summer, less electricity for lighting and heat is required than in winter. Also during one day come to large fluctuations. So, a tip of the electricity requirements of a public network especially in the morning between 6-8 clock to notice between 11-13 and between 19-22 clock clock. Electrical energy can not be stored to any significant extent until today. It follows that production and consumption of electrical energy must always be in balance. This leads to a complex and costly regulation of network and power plants. Nature of the production and the need for regional power grids are offset by a number of regional power grids are interconnected and pumped storage power plants are used as an energy buffer. In Europe, the high-voltage grids in the Association of European Transmission System Operators, formerly switched (short ENTSO -E) together UCTE. The regulation of the grid frequency via two coordination sites in brewing Weiler ( Pulheim ) / D and running Castle / CH.

Power plant types

Main article: Kraftwerk

Subdivision according to the load of responsibility

  • Base load power plants:
  • Medium load power plants:
  • Peak load power plants:
  • Discontinuous power producers

Subdivision according to the energy source

  • Fossil energy:
  • Power plants with renewable energy sources
  • Wind turbines
  • Photovoltaic
  • Geothermal
  • Biomass power plants

Heat recovery

Heat -generating power plants in addition to the generated electric power also make remaining residual heat:

District heating power plants can only be near population centers realize, since the heat generated must be removed in the immediate area. District heating power plants are often combined with steam power plants, but can also be operated individually. When the thermal power stations, the remaining energy of the water is used at the turbine outlet. The steam is not cooled down to ambient temperature but is fed at a higher temperature level by large pipes in a district heating network. At the consumer, the steam then its heat and comes as water of a lower temperature back to the power plant back.


  • Main article: Power Plant Management

Current is generated by the rotor of a generator is placed in a rotational movement. In large power plants, these generators are exclusively synchronous machines. Such a synchronous machine is produced by means of its rotor in the winding a direct current flows, a rotary field. This field induced in the three windings of the stator three systems at 120 ° phase-shifted sinusoidal voltages.

If now the current requirement of a power system increases, the generator needs to perform better. So, for example, has a greater power to the generator, the steam or water turbine. If it does not, the generator due to the greater resistance will run slower. Thus, including the frequency changes - it becomes smaller until the load shedding. The frequency is thus a characteristic feature which describes the power requirements of a network. And indeed, power plants are governed by the frequency of the power grid. If it is too low, the steam or gas turbines have to bring more power. If it is too high, the power is reduced.

For this complicated regulation technique is needed. In a large power grid, many power producers are related. Among themselves now matched the amount of current required must be provided.

Actually, however, the provision of current depends on still further elements. The German electricity market is liberalized in April 1998 since the implementation of the Energy Act and electricity on the power exchange EEX (European Energy Exchange) in Leipzig as a commodity traded. Large energy companies ( E.ON, RWE, Stadtwerke etc.), but also consumers and industrial companies buy electricity a power plant operators. Depending on how much electricity a utility company that is sold, he will also produce.

Energy transport

In addition to the generation of electrical energy whose transport is a further area of energy technology. Electrical energy is transported to the power supply in the form of alternating current from the generating plants to the individual consumers. Usually, the use of three- phase alternating current is in the form of three-phase high voltage transmission, due to the potential savings of conductor material over a single-phase alternating current.

In order to minimize transmission losses, high voltages are used for the transport of electrical energy and it is attempted to produce the electric power as close to the consumer.

In order to minimize transmission losses, the electrical resistance of the conductor as well as the current strength must be decreased.

Conductor cross-section

The resistance of the conductor can be reduced by larger conductor cross-sections; it sinks in doubled diameter of the conductor to a quarter of the original value. This method reaches its limits, however, as this amount of material used for the metallic conductors increases, and, particularly for overhead lines, mechanical problems such as the weight of the conductors play an essential role. For AC and three-phase systems also counteracts the skin effect.

The resistance of the conductor can also be reduced by improving the materials.


Therefore, a lower current intensity and also a higher voltage by the same factor is used for the same performance, which leads to the high-voltage lines. The power grid is divided into to various network levels (high voltages for long distances, lower for short distances ). Between the individual lattice planes are power transformers in substations of voltage conversion.

However, even here the surmountable routes are limited, as the voltage can not be arbitrarily high transformed: the higher the voltage, the more difficult it is to interpret the insulation and there are additional losses due to gas discharges such as corona discharges. In addition, the capacitive reactive current of a line increases in proportion to the square of the voltage. This leads to a reactive power consumption of the transmission line, which is already in the idle can utilize a substantial part of the line in response to the capacitance per unit length and the length of the conduit. The stranded conductor is now acting as a transmitting antenna and generates electrical and magnetic fields whose constant reloading generated significant losses.

For underground cables (as well as submarine cables ), which naturally have a large capacitance per unit length ( the surrounding soil has a much higher dielectric constant than air), it means that the cable runs are limited to about 70 km. Therefore, the high -voltage direct current (HVDC ) is with long cable runs, as they are common in submarine cables, are used. However, the HVDC has the technical disadvantage of being able to transport electrical energy only between two points, and requires technique and expensive converter stations for converting DC into AC. In addition, a large-scale, meshed transmission network with multiple branches and cross-links at DC operation technically not possible because, in contrast to AC systems or three-phase networks, the power flows using phase shifts can not be controlled.


Is the electrical power loss

(.. Voltage .. current .. electric resistance)

That is, a reduction in the current affects even square.