Alternating-current electricity transmission requires reactive power, which is primarily provided by large power plants. Reactive power supports grid voltage during long-distance, large-scale power transmission. By using reactive power, the grid voltage can be increased or decreased, and electricity can be efficiently transmitted. These large electricity transports are necessary when wind power from northern Germany is needed in its industrial south. Because of the energy transition, many of these large power plants in Germany were shut down. Grid operators like Amprion GmbH, Dortmund, Germany, responded by installing reactive power compensation systems.
Amprion commissioned Siemens, Munich, Germany, to build two reactive power compensation systems for the important Kriftel power grid node: a mechanically switched capacitor with damping network (MSCDN) and a power-electronic static synchronous compensator (STATCOM). The systems have been running successfully in test operation since December 2018. They are able to dynamically, rapidly, and flexibly increase or decrease the grid voltage on demand, which is necessary to keep the grid stable despite the increase in fluctuating power supplies from renewable and distributed energy sources. At the same time, the system helps prevent gaps in supply because of large power plant shutdowns. The Kriftel substation between Frankfurt and Wiesbaden controls power distribution for the Greater Frankfurt Area and its almost-six-million inhabitants.
Siemens also built its first advanced power insulated gate bipolar transistor (IGBT) modules in Kriftel. These IGBT power transistor modules can supply more power than its previous modules, which means that fewer modules are required for the specified control range than was formerly the case.
“We are pleased with the successful test operation of what is so far Europe’s most powerful SVC PLUS (Static Var Compensation) system, which we have supplied to our customer, Amprion, on a turnkey basis,” says Mirko Düsel, the CEO of the Transmission Solutions Business Unit in the Siemens Energy Management Division. “Static VAR compensation systems, based on our SVC PLUS technology, is highly advanced and is also ideal for flicker compensation, integration of wind power plants, or railway electrification.” Amprion placed its order in early 2016.
The core of SVC PLUS, an advanced STATCOM, is its multilevel converter technology. By contrast with other self-commutated converter topologies, the voltage wave shape produced by SVC PLUS is practically sinusoidal because of the multilevel technology. This makes the low-frequency harmonic filters, often used in earlier solutions, superfluous and substantially reduces the space requirements for the overall unit. The average availability of a Siemens SVC PLUS system far exceeds 99% and the company has already received orders for more than 100 SVC PLUS systems worldwide.