Single-Wire Earth Return

Under the English term Single-Wire Earth Return ( abbreviated Swer ) is understood in the electrical industry a form of electricity network, which serves as the electrical supply by vast, rural areas and is characterized by particularly low cost. Applications of this form of implementation in the rural areas, for example, Australia, New Zealand, North America, such as in Canada, Brazil, India and some countries in Africa such as South Africa and Mozambique. In Europe, this form of electrical power supply networks does not occur, since continuous three-phase AC power is available to the end user here.

Construction

The Swer system is one of the single-phase three -wire systems, as it provides connections to customers only single-phase AC voltage and no three-phase AC voltage. It uses as an essential feature at medium voltage only an electrical conductor, typically implemented as an overhead line, and as operational return conductor for grounding. This simplifies the construction of these supply lines is particularly cost- feasible, since in three-phase networks at least three wires must be routed. Since leads to high voltage side of the grounding operational current, the primary disadvantage Swer networks is to ensure necessary for the operation of low earth resistance. Swer networks have in Australia, the so-called Outback, spatial extents per segment of up to 300 km, which corresponds to approximately ten times the size of the usual in Central Europe medium voltage networks.

In Australia, the transformers used in the context of Swer are defined in the Australian Standard AS2558 - 2006.

The Single-Wire Earth Return is fed into the regional substations from the parent voltage levels, which are constructed through a three -phase system by means of special single-phase isolation transformers with ratings of some 100 kVA up to some 1 MVA per strand, as shown in the adjacent figure. The voltages of the high voltage side be, depending on the region differently, 19.1 kV or 12.7 kV. This single-phase AC voltage is supplied to the local transformer stations, which are typically carried out in those regions as a mast transformer. This local transformer supplies the single-phase three-wire system and generates the certain for the end customer low voltage of 240 V twice (eg in Australia) or twice 110 V (eg in Canada). Larger consumers such as air conditioners are connected to the low tension between the two outer conductors, which double the voltage results.

Disadvantages

Besides the problem with ensuring a good electrical conductive ground connection Swer has a distributor network of single-phase AC voltage to no rotating field. This allows powerful electrical machines, such as the induction motor can not be operated directly from the mains and need additional frequency or afflicted with handicaps Steinmetz circuit. Single-phase asynchronous motors can be operated as capacitor motors, AC motor and shaded pole motor, however, are used without any problems, but have little power. Furthermore, the losses are inherently higher than for the same material used in a similar three-phase power in a single phase. Due to the large expansions have continued to occur larger variation of mains voltage to the end user terminals. Partial specific rule transformers must be used to compensate.

Furthermore, it comes through the Swer on the parent three-phase systems strengthened to balance loads and thus instability in the electricity network, since the division can take place only in large blocks of Swer strand to a single phase of the three-phase network. The possibility to compensate typically occurring on overhead lines simple ground fault without power failure, for example, in the context of earth fault, is in Swer not possible: If there is a ground fault of the conductor, an electrical short circuit and a resulting power failure are immediate consequences.

Similar applications of this concept

In the monopolar high-voltage direct current transmission ( HVDC) cable, such as is also used in the Baltic operatively the earth electrode as a return line. Other similarities to Swer system do not exist. The power supply of the Strausseefähre falls into this category.