Underfrequency
In electrical power engineering, an underfrequency is a network frequency that is lower than the target network frequency. The target network frequency of three-phase networks in Europe is 50 Hz.
An underfrequency in a power grid occurs in particular in the event of a sudden increase in load or the sudden failure of power plant output, since the load difference is covered by the kinetic energy of all rotating masses in the generators . As a result of the loss of kinetic energy, the rotor speed of the generators decreases and thus also the frequency of the generator voltage output. The deviation of the actual from the target network frequency is more serious than the voltage drop that occurs at the same time .
activities
Frequency deviations are usually compensated for as part of the regulation of the power supply. In an emergency, the grid frequency can also be stabilized by the targeted shutdown of individual bulk customers or regional shutdowns by the network protection in order to avoid a major power failure .
Germany
To avoid a network breakdown due to underfrequency, Germany has a 5-step plan for load shedding . This is described in the " Network and system rules of the German transmission system operators " in Chapter 7.3.4.
| step | frequency | Measures for compensation or protection |
|---|---|---|
| 1 | 49.8 Hz | Use of control reserve |
| 2 | 49.0 Hz | Immediate shedding of 10–15% of the network load |
| 3 | 48.7 Hz | Immediate shedding of a further 10–15% of the network load |
| 4th | 48.4 Hz | immediate shedding of another 15–20% of the network load |
| 5 | 47.5 Hz | Network separation of the power plants |
Electronic frequency relays are required for automatic load shedding of levels 2 to 4 . At level 5, all power plants must automatically disconnect from the grid; the immediate consequence is a complete collapse in supply. Larger caloric power plants and nuclear power plants try to cope with their own needs by reducing their output and to maintain this non-optimal operating state for a few hours. If the control does not succeed in catching and maintaining the power plant's own consumption, the affected power plant units are switched off, which leads to a longer time for restarting.
Austria
In Austria, the “phased plan for frequency problems” defined by E-Control also applies .
| Measures in the generation area | from 49.8 Hz to 49.3 Hz | Alerting the staff, using the power plant capacity that has not yet been mobilized, automatic initiation of pump shutdown programs (for example of pumped storage power plants). |
| Measures in the network user area | from 49.0 Hz to 48.2 Hz | Gradual reduction of the network active power to up to approx. 40% of the power before the fault occurred. |
| Power plant shutdown measures | from 47.5 Hz to 45 Hz | Shutdown programs for disconnecting machine sets for the power plant's own use. |
| End of mains supply | below 45 Hz | Separation of the power plants from the grid. |
As a result, an attempt is made to bring the power supply network back into operation in stages by means of targeted switching and to synchronize sub-networks. Above all, black-start power plants such as run-of- river power plants , pumped storage power plants and gas turbine power plants play a special role. These power plants can start without an external supply of electrical energy and thus provide the power required to start power plants that cannot be black-started, such as coal-fired power plants.
Web links
- Network and system rules of the German transmission system operators , Version 1.1, August 2007 (PDF; 622 KB)
Individual evidence
- ↑ Energie-Control GmbH (Ed.): Technical and organizational rules for operators and users of networks . Part E: Technical measures to avoid major disruptions and limit their effects. Vienna March 1, 2008, 7.1, p. 31–34 ( e-control.at [PDF; accessed on January 9, 2009]).