A debate is currently raging as to whether Germany will be able to achieve its climate target for 2020 of reducing emissions of the greenhouse gas carbon dioxide by 40 percent compared to 1990 levels. Meanwhile, the country continues to rapidly expand its use of renewable sources of energy. The German Association of Energy and Water Industries (BDEW) has calculated that renewables covered 28.5 percent of Germany’s electricity needs in the first half of 2014 — a new record. However, the increase in eco-electricity poses a challenge to grid operators, because every new wind or photovoltaic system is an additional electricity producer that has to be directly connected to the grid.
Although it wouldn’t be a problem for grid operators under normal conditions, the situation becomes tricky if a short circuit occurs because an excavator accidentally cuts through a power cable or a tree falls on a power line. The more electricity producers are directly connected to the grid, the more current could flow through the power lines. If short-circuit current flows unhindered into switchgear, it could tear the power lines out of their mountings and fry grid components.
To prevent this from happening, the power lines that lead to transformer substations and switchgear are equipped with short-circuit protectors known as circuit breakers. If a short-circuit current rapidly builds up, circuit breakers can generally interrupt this flow of electricity, provided it is not too large. Additional protection against especially powerful short-circuit currents is provided by series reactors, which damp short-circuit currents like a resistor. The problem with series reactors is that they not only act as resistors when there is a short circuit, but also during normal operation. This causes electricity to be continuously wasted. The power loss typically amounts to 25 kilowatts per series reactor coil. Experts estimate that up to 44,000 series reactors are installed worldwide. That translates into a global power loss of up to 1,100 megawatts, which is the equivalent of a large power plant’s output.