A substation (also known as a substation ) is part of the electrical supply network of an energy supply company and is used to connect different voltage levels . In addition to power transformers, substations always consist of switchgear , constructed as an open-air switchgear or in an encapsulated form as a gas-insulated switchgear and other devices for measuring and control technology. Systems without transformers are also referred to as load distribution plants (load distribution or switchgear).
Due to the high degree of automation, the operation in many substations, such as the execution of switching operations, takes place fully automatically on site.
In order to transfer the electrical energy from the power plant to the consumer with as little loss as possible, the electrical energy is transported over several voltage levels. The optimal voltage level is selected depending on the power to be transmitted and the distance. In the substation, the electrical energy is transformed between two or more voltage levels. The voltage levels can be divided as follows:
- Supraregional transport networks (220 kV or 400 kV and larger or with high-voltage direct current transmissions ). The systems are mostly open-air systems, sometimes also indoor systems.
- regional transport networks (110 kV). Outdoor or indoor systems in cities.
- Local distribution networks (30 to 60 kV), mostly indoor systems.
- Supraregional / local distribution networks (6 to 20 kV) mostly indoor systems.
A minimalist substation in Dülmen
Substation in Lauscha , 1925/26
Substation in Vienna-Favoriten , 1929
In addition to the transformers required for the transformation, the substation also has switchgear for the high and low voltage lines. The technical equipment ( power transformers , busbars, etc.) as well as the lines are usually designed redundantly , so that the supply is still guaranteed in the event of a failure of an item of equipment .
The term secondary technology includes the equipment of a substation that is not directly involved in the transformation. However, this includes functions that are very important for operation, such as:
- Local control (control of the individual switchgear panels on site, usually via a field control cabinet)
- Voltage regulation (keeping the mains voltage constant under different load conditions)
- Grid protection (monitoring of the lines for short circuits or earth faults with disconnection of the line concerned)
- Energy metering
- Remote measurement (remote transmission of measured values to a remote network control center )
- Remote control (remote control and monitoring by a remote network control center)
- Own use (secured DC and AC voltage supply, battery systems, rectifiers and inverters to maintain the function of the system even in the event of a power failure or network disruption)
- Ripple control system (control of the consumers in the network; load management )
A special form of a substation (UW) is the simplified substation (VUW). While the lines and transformers are switched on busbars in the most common conventional substations , in simplified substations i. d. Usually there are no busbars on the high-voltage side. In this case, the lines are only connected directly to the transformer via disconnectors and circuit breakers . A coupling between the lines is possible. VUWs are used to save costs when there are only a few (two to three) lines on the high-voltage side (omission of the busbar and thus savings on busbar disconnectors).
This fact also gives rise to the disadvantages of VUWs: Since there is no busbar as a "distributor", if a line fails, the connected transformer would also become useless (with VUW without coupling between the lines). The failure of system parts or lines is more complicated to compensate for. Subsequent expansion of the system is only possible to a limited extent. If an additional line is to be connected, an additional coupling (if this is important) and / or an additional transformer is required. With several additional lines, the cost advantage is therefore quickly used up. In such a case, the VUW often becomes a conventional substation by installing a busbar.
In the case of large substations for several voltage levels above 100 kV, it is sometimes necessary to accommodate the system in several separate areas in the immediate vicinity, which are connected to one another via coupling lines. As a rule, each area contains the complete switchgear - mostly including the transformers - for this level and is completely fenced in. The line connection between the system parts is usually made via overhead lines, less often via underground cables. Examples of such divided substations are the Hoheneck substation in Ludwigsburg and the substation in the Krone von Witten district.
Large substations (highest applied voltage over 100 kV) must be accessible for heavy transports, as large transformers can weigh up to 500 t. Because of the size of the transformers, the driveways shouldn't be too narrow either. Some, especially older substations for 400 kV or 220 kV also have their own rail connection for the delivery of the transformers.
Listings of switchgears and substations can be found in the following lists:
- List of switchgear in the extra high voltage network in Germany
- List of switchgear in the extra high voltage network in Austria
- List of switchgear in the high voltage network in Switzerland
- Wilfried Knies, Klaus Schierack: Electrical systems engineering. 5th edition, Carl Hanser Verlag, Munich and Vienna, 2006, ISBN 3-446-40574-7 .
- Günter Springer: Expertise in electrical engineering. 18th edition, Verlag - Europa - Lehrmittel, Wuppertal, 1989, ISBN 3-8085-3018-9 .