Switchgear
A switchgear is a system in which electrical energy is distributed or converted.
General information
Switchgear, more precisely their busbars , form the "nodes" of the high , medium and low voltage networks . The lines arriving and leaving the node are called branches. A distinction is made between branches for infeeds, outlets and couplings to other network nodes. Because of the large number of branches and the connection space required for the large cable cross-sections, the "nodes" are implemented as busbars. Practically all branches of a switchgear are connected to the network nodes via switching devices.
The actual power distribution and the grouping of loads or consumers take place in the switchgear . Switchgear enables the network topology to be changed in the event of malfunctions and the isolation and earthing of equipment for maintenance work. A distinction is made between low-voltage, medium-voltage and high-voltage switchgear.
Cable gardens are also counted as switchgear, although they only have disconnectors, if at all.
Switchgear requirements
- Ensuring safe operation
- Encapsulation, partitioning and covering of high-voltage parts (indoors)
- Separation and earthing option for maintenance work
- Serviceability
- little need for space
- Long-term integrity of contact connections
- Limitation of the heating of live parts
- For open-air systems, an extensive grounding network and lightning protection devices
Low and medium voltage
Switchgear for low and medium voltage are always installed in closed buildings. While switchgears for low voltage are housed in closed cabinets in normal rooms, switchgears for medium voltage are often located in suitable switch rooms in so-called switch cells, which are connected to one another with so-called busbars. Depending on their importance, these are equipped as a single busbar (with longitudinal separation), double busbar or even triple busbar.
The spatially separated arrangement of the busbars enables work in a switchgear cubicle in compliance with certain safety rules . Only the cable / line that supplied the cell has to be switched off and grounded . When designing a busbar, Al or Cu bars are used which must carry the maximum permissible continuous load current; this applies to the rails themselves as well as to screw connections to one another and the phase branches to disconnectors , circuit breakers and other equipment.
Since the aluminum rails tend to flow under the action of the contact pressure produced by steel screws, the heating during operation gradually deteriorates the rail screw connections until they are destroyed. The consistent use of clamping disks made of stainless steel (Niro) keeps the rail contact forces constant by expanding the clamping disk in length. The arrangement of the steel screws with overlapping rails are regulated according to VDE regulations.
Modern medium-voltage switchgear are fully encapsulated d. H. all active parts such as busbars and switchgear are inaccessible during normal operation. This requires a largely maintenance-free structure of the busbar connections and the switching devices. The gas SF 6 (state-of-the-art) is used as the insulating medium for the hermetically sealed busbar space in gas-insulated switchgear, or solid insulation made of various cast resins in the latest design. Switchgear systems with alternative gases (based on fluoroketones) or with vacuum as the insulation medium are also used. Switching devices are designed as vacuum switching devices or also with gas insulation, depending on the rated voltage and short-circuit breaking capacity.
If great flexibility is required when setting up the fields (e.g. several functions per field), classic switchgear with air as the insulating medium offers more freedom for planning and expansion. They are mainly used in industry, where standardized compact switchgears reach the limits of their possible functions. For these switchgear systems, largely maintenance-free switchgear in design with vacuum switch as gas-insulated switchgear (GIS) are available. In the case of new constructions and upgrading of transformer stations, on the other hand, standardized compact switchgear (ring cable switchgear with one to three transformer outlets) with solid insulation or in GIS design are mostly used.
High and very high voltage
Switchgear for high and extra high voltage are built either as outdoor switchgear or as gas-insulated switchgear . The main difference is that an insulating gas such as SF 6 is used, which means that the completely encapsulated switchgear can be set up much more compactly and in a smaller space.
The space requirement of gas-insulated switchgear is about 1/10 that of outdoor switchgear, which means that these systems can be housed in halls. However, costs and maintenance are higher than with outdoor switchgear, which is why gas-insulated systems are mainly used in densely built-up urban areas with little space.
Special switchgear
Special switchgears are converter stations for high-voltage direct current transmission (HVDC) and traction current converter stations . Another form of special switchgear is found in the antenna switches of large transmitters with switchable directional characteristics. Carrier frequency signal relay stations or systems for decoupling carrier frequency signals are also a special type .
Safety rules
Unauthorized persons are not allowed to enter switchgear due to the danger of the partly accessible high voltage parts. In Germany, the systems must be equipped with locked doors that can be opened from the inside ( panic lock ). Outdoor switchgear must be surrounded by a 1.80 meter high fence, which is often connected to the station ground or a separate potential control ring. Access to the areas with high-voltage systems is only possible for appropriately trained persons.
history
The first designs were very simple: all the necessary components were attached to a wall. When systems were later installed on wooden panels , it was possible to speak of switchboards in the narrower sense for the first time . To avoid fires was wooden finally slate or marble replaced. This went hand in hand with further progress, because the switching and measuring devices could be attached to the front, while the cabling was done on the rear.
While in the early days of the switchgear staff were working on site to carry out the individual switching operations manually, in the first half of the 20th century both switchgear and substations were increasingly remotely controlled from central control centers using control technology. Nowadays, switchgear and transformer stations are among the systems with the highest degree of automation: Up to a few 100 switchgears and transformer stations are automatically controlled and remotely monitored from a central control center. Personnel are only on site when necessary, for example for maintenance work.
See also
literature
- Manfred Lindmayer (Ed.): Switching devices. Springer, Berlin 1987, ISBN 3-540-16706-4
- Adolf J. Schwab: Electrical energy systems - generation, transport, transmission and distribution of electrical energy , Springer, 2006, ISBN 3-540-29664-6
- Hennig Gremmel (Ed.): ABB switchgear manual. 11., rework. Ed., Cornelsen, Berlin 2006, ISBN 978-3-589-24102-6
- Allgemeine Elektricitäts-Gesellschaft (Hrsg.): AEG auxiliary book for electrical light and power systems . 6th edition. W. Girardet, Essen 1953.
Individual evidence
Web links
- Switchgear at the Berlin Energy Museum