Natural performance

The natural power is a term used in electrical power engineering at with AC -powered electricity grids . If the complex line impedance of an electrical line ( high voltage line ) corresponds to the complex load resistance of the electrical consumer connected to the line, an adapted line is available. The electrical power transported via the adapted line is called natural power. ${\displaystyle {\underline {Z}}_{L}}$ ${\displaystyle {\underline {Z}}}$ ${\displaystyle P_{N}}$

General

Reactive power demand Q for a kilometer in length of a 380 kV overhead line, underground cables and GIL depending on the transmission power S . With inductive reactive power , Q  > 0, with capacitive reactive power, Q  <0

The natural performance does not represent a limit performance which must not be exceeded. Rather, it describes the optimum operating point at which the generator in the power plant does not have to provide an additional reactive power component for the line . If more power than the natural power is transmitted via the line, as shown in the adjacent sketch using the example of a 380 kV overhead line, it behaves inductively with a positive reactive power requirement , including capacitive with a negative reactive power requirement, and resistive ( ohmic ) with exactly natural power . In the diagram, the natural power corresponds to that transferred power at which the reactive power requirement is 0  Var . ${\displaystyle Q}$ ${\displaystyle S}$

However, since it is not possible in power supply networks to constantly induce the sum of the individual consumers (electricity customers) to only use the natural power , the natural power is adapted to the consumer power. This is possible with the help of reactive power compensation of the line, which in principle amounts to changing the complex resistance of the line. To do this, it is necessary to connect coils or capacitors at the beginning and end of a high-voltage line . In high-voltage networks, however, in practice almost exclusively compensation chokes are connected to the high-voltage transformers via special windings in order to reduce the operating capacities of the high-voltage line accordingly if necessary. ${\displaystyle P_{n}}$ ${\displaystyle {\underline {Z}}_{L}}$

Formally, the natural performance is given as: ${\displaystyle P_{N}}$

${\displaystyle P_{N}={\frac {U_{N}^{2}}{|{\underline {Z}}_{L}|}}}$

With the nominal voltage and the line impedance of the line. ${\displaystyle U_{N}}$ ${\displaystyle {\underline {Z}}_{L}}$

Values ​​for overhead lines

The following table gives examples of some natural outputs of typical overhead lines in different voltage levels:

Nominal voltage in kV	natural power in MW
20th	2.4
110	32
220	180
380	425

With the same line impedance (wave impedance), the natural power increases with the square of the voltage towards higher voltage levels. Deviations from this relationship arise due to the structure of the different line wave resistances of high-voltage lines. A reduction in the wave resistance in order to achieve a higher natural output is achieved, among other things, by bundle conductors , which are preferably used in higher voltage levels.

Underground cables

In cable systems such as a 380 kV underground cable , due to the high reactive power requirement, the natural output could only be achieved with additional forced cooling. For example, the natural output of a 380 kV underground cable system with a conductor cross-section of 2,500 mm² is around 3,000 MW, which is above the thermal limit of the underground cable. For gas-insulated pipelines (GIL) with a conductor cross-section of 6,300 mm², the natural output is around 2,300 MW, which is also a multiple of the natural output of the overhead lines from the table above. As a rule, however, the natural performance is not achieved with cables, as they reach their thermal limits beforehand. That is why they are not dimensioned according to their natural output, but according to the thermal limit output.

literature

• René Flosdorff , Günther Hilgarth: Electrical energy distribution . 9th edition. Teubner, 2005, ISBN 3-519-36424-7 .

Individual evidence

1. ^ BR Oswald: Expert opinion on the 380 kV Salzburg line: Effects of the possible cabling of the Tauern-Salzach section . Institute for Energy Supply and High Voltage Technology, University of Hanover, 2007, Chap. 5.1, p. 12 ( online ).