The regulating transformers are in operation, protecting the network against congestion


The transmission system operator officially launched the PSTs (phase-shifting transformers, transformers with phase regulation). By installing them, ČEPS secured safe and reliable operation of the entire electric power system of the Czech Republic, and solved the operational aspect of the critical problem of unscheduled flows from Germany. The launch of
the transformers, however, does not mean that the issue of unscheduled flows is completely resolved.  

The experience of operating the PSTs has been positive so far. Since its partial launch
in mid-January, for the first half of this year alone these machines have helped reduce the flows through our transmission system on 73 days.

“The launch is also welcomed by our foreign partners. Although the primary task of these transformers is to protect our transmission system, the regulatory taps’ settings are coordinated with the neighboring network operators in order to ensure the reliability of the operation of electricity networks throughout the region of Central Europe. It is possible to adjust the regulation in real time depending on the current situation in the network,” said Jan Kalina, Chairman of the Board of Directors of ČEPS, a.s.

On Tuesday, June 6, dispatchers diverted power to the 23rd angle regulation steps, which is
the greatest number since the launch, but still having enough backup even in such a tense situation (there is a total of 32 steps, which means flow limitation up to 900 MW). This was due to a critical operating situation. Specifically, there was a lack of electric power in the Balkans, with the system of the Czech Republic also having a deficit of around 1,000 MW due to
a number of sources being unavailable, while there were also large overflows across
the continent from northwest to southeast.

Earlier, a reversed regulation was applied at the request of the German operator 50Hertz in
a situation where the German system struggling with a critical operating situation could be relieved by a forced flow into our network.

“Such an approach will continue to be applied in the future. That is, provided that our operating conditions are capable to prevent any deterioration of the situation in our network,” said Kalina.

ČEPS is not preventing electricity flowing through our transmission system. It aims to transfer
the maximum amount of electricity, but safely, without compromising the reliability of the power supply in the Czech Republic.

“The Czech Republic has been long drawing attention to the problem of unscheduled flows of electricity both in bilateral discussions with representatives of the German government, and at
the EU level. I consider it essential that the ČEPS Company undertook long-term complex, but successful negotiations with the German transmission system operator of these transformers so as to ensure the reliability of the electricity networks operation in the region,” said Jiří Havlíček, Minister of Industry and Trade, during the official launch. 

The operation of the PSTs by the transmission system operator also saves the cost of corrective measures that would have had to be used to maintain the flows at the safe level.

“Without the PSTs, international redispatches would be massive and costly. Now we can save tens of millions of crowns a year,” said Kalina.

The investment costs of the construction totaled to CZK 1.588 billion. The construction of
phase-shifting transformers required not only the purchase of the devices, but also a project preparation and a significant expansion of the Hradec u Kadaně substation.

The Czech and German substations are connected by two 400 kV power lines. Two PSTs are connected in parallel on each of the lines.

Phase-shifting transformers are machines that are used to control the power flow of real power through manipulation of the phase angle of the voltage between the transmitting end and
the receiving end of the line. Put simply, if we imagine the transmission system as a reservoir with many tributaries and distributaries, the PST works as a floodgate, which reduces, or increases the flow in the given distributary. Reducing the flow on one power line results in redistribution of flows. Since electricity takes the path of least resistance, part of the flows will move to other power lines with more available capacity, thus eliminating possible overloads in the transmission network. The PSTs shall ensure the safe operation of the transformers in our transmission system not only in times of extreme transit flows, but also during long-term limitation of transmission capacity due to extensive reconstructions of power lines.     

Six years ago, in November 2011, the Czech transmission system recorded the first of a series of critical situations, when both Czech and German operators have exhausted all available means for the regulation of unscheduled flows and the Czech system was on the brink of collapse without being able to change the situation. Their cause largely lied in the uncoordinated construction of renewable energy sources, in particular in Northern Germany (in the Baltic and the North Sea), decommissioning of nuclear sources in the south of the country and at
the insufficient capacity of transmission lines. High demand for cheap electricity in Austria and the southern European countries has resulted in a significant increase in commercial exchanges of electricity in the direction north-south. Due to the absence of a physical link inside Germany, part of the physical flows induced by these transactions were transmitted also through
the neighboring (especially Czech and Polish) transmission systems. The capacity of such unscheduled flows, often comprising up to half of the market flows between Germany and Austria, in extreme cases exceeds the safe levels and leads to the overloading of the network elements.

Key milestones

The Ministry of Industry and Trade and the Energy Regulatory Office were informed about
the decision to build PSTs.

The Ministry of Industry and Trade, the sole shareholder of ČEPS, approved the construction of PSTs at the Hradec substation.

The tender for PST supplier was completed.

The construction of PSTs started.

The test run of the PSTs was followed by their commissioning.

Phase-shifting transformers in figures

​Project implementation timeframe​2015-2017
​Costs​CZK 1.588 billion
​Number of devices​4
​Disposition of a single PST device​2 units (series and shunt)
​Transport weight of one unit (without oil)​300 t
​Shunt unit weight​430 t
​Series unit weight​445 t
​Number of angle regulation steps​+/- 32
​Dimensions of a complete PST​22.9 x 14.4 x 9.9 m

Press Release