Picture: TU Dortmund

Real-time simulation in the smart grid laboratory

How does our power grid handle the fluctuating voltage from wind energy or photovoltaics? How does it behave when a large number of electric cars are charging at the same time? The new Smart Grid Technology Lab at TU Dortmund University is conducting research on these current issues. At ie³, the Institute for Energy Systems, Energy Efficiency and Energy Economics at the Technical University, various grid situations are realistically simulated in the laboratory. A transformer that compensates for inadmissible voltage fluctuations – and does so fully automatically on the basis of a predefined control algorithm – was required for transmission from the medium-voltage to the low-voltage grid in the test environment. Ormazabal supplied a controllable local network transformer (rONT) for this purpose, the control of which was specially tailored to the requirements of the laboratory. Ormazabal was able to draw on the experience of its own smart grid laboratory, which the company operates near its headquarters in Spain.

With the Smart Grid Technology Lab at TU Dortmund University, an infrastructure has been created that makes it possible to develop and test smart grid components in an environment that corresponds to current and future grid operations. “The special feature of this laboratory infrastructure is, on the one hand, the replication of a power system across grid levels. On the other hand, the interaction of loads, feeders and storage systems with the grid operating equipment, measurement and communication technology as well as protection and control technology is taken into account. Among other things, these aspects are necessary for investigating the future provision of system services from the distribution grid,” explains Dr. Jonas Maasmann, research group leader at ie³. “For this purpose, a physical, ‘real’ smart grid system landscape is available, which can be supplemented and scaled with the help of real-time simulation.” The Smart Grid Technology Lab at ie³ is funded by the German Federal Ministry for Economic Affairs and Energy.

Wanted: Special solution with 10 kV/10 kV transformer

The TU Dortmund commissioned the energy company Uniper Anlagenservice GmbH to set up the test environment. In order to simulate different grid-standard feed situations, e.g. the connection of a DC fast charging station for electric cars, an adjustable 10 kV/10 kV transformer with a voltage band of +/- 10 % should be used for the input side. A 10 kV/0.4 kV rONT was provided for the output side. “While transformers with this voltage are standard, the transformer with 10 kV/10 kV was a special service that not everyone on the market offers,” says Stefan Thier, project manager at Uniper Anlagenservice GmbH. “In Ormazabal, we found a partner who offered us both from a single source.” Another prerequisite for use in the Smart Grid Technology Lab was that the transformer could be switched and controlled remotely.

Found: Ormazabal-rONT with on-load tap-changer

The adjustable local network transformer combines an intelligent control system with the so-called on-load tap changer (OLTC): an automatic load tap changer developed in-house by Ormazabal that can adjust the voltage in steps of 2.5%. “Solutions with a servomotor that must be externally regulated are common on the market. Compared to conventional, non-controllable transformers, our rONT can change the transformation ratio from the medium to the low-voltage network under load,” explains Stefan Henkenmeier, sales representative at Ormazabal. “In this way, the rONT compensates for unacceptable voltage fluctuations, such as those caused by the integration of distributed generators, and prevents any resulting damage at the low-voltage distribution level.” The transformer reacts fully automatically and without manual intervention to changing voltage conditions and ensures a constant output voltage via medium-voltage regulation.

trainer with remote control

A special control algorithm makes voltage equalization possible. “As part of the research facility, there were special requirements for components and their communication with regard to the entire system integration. In addition, special interfaces were necessary for research questions on control algorithms of rONTs in the smart grid,” says Dr. Jonas Maasmann. “Here, it was important to ask about the expectations of the operator and the partners as early as the planning phase,” adds Stefan Henkenmeier. “In order to regulate the control of the rONT via certain protocols, adjustments were finally necessary. In cooperation with our colleagues in Spain, the program for controlling the adjustable transformer was rewritten accordingly.” The tests can now be run remotely from the control station of the Smart Grid Technology Lab using a SF6 gae630 switchgear. “The encapsulated switchgear and the safety concept implemented by Ormazabal also ensure safe operation of the plant,” confirms Dr. Jonas Maasmann.

Profiting from the know-how of the group of companies

The research group leader of the TU Dortmund University had visited the Research and Technology Centre (CIT) of Ormazabal near Bilbao together with institute colleagues. A high-performance test facility and a large-scale real-time network test facility there provide a safe and controlled environment for testing and developing new technologies and products. The experience gained at the CIT has been instrumental in developing an individualized solution for the Smart Grid Technology Lab. Dr. Jonas Maasmann sums up: “Ormazabal has provided excellent support to TU Dortmund University as the supplier of the ‘controllable local grid station’ test stand in the development of the Smart Grid Technology Lab. Ormazabal did not see itself merely as a supplier, but actively contributed its expertise in plant construction in cooperation with the general contractor involved. Above all, we were also able to benefit from the experience of the innovative solutions from Ormazabal’s laboratory facilities”.

System test successfully passed

From the initial enquiry to the commissioning of the components, just under a year passed with intensive consultation and joint planning. During the commissioning of the plant, a complete system test was carried out. Both rONT were first tested by manually changing the step value. In a second step, the automatic control algorithm was tested by manually changing the primary voltage at one rONT. The other rONT automatically compensated for these voltage fluctuations so that the secondary voltage remained within the defined control band.

“During operation, it becomes apparent that the systems brought in by Ormazabal are very reliable and well thought-out. The scientists in the research group enjoy working with the system and the coordinated safety concept ensures safe operation,” concludes Dr. Jonas Maasmann. Stefan Thier from Uniper Anlagenservice GmbH also draws a positive conclusion: “The project went satisfactorily, especially with regard to the services for the necessary adaptation of the algorithm. The project was very exciting for us, we had never worked with rONT before, especially not in such a test world as the laboratory, far away from industry standards.”

Ormazabal is one of the world’s leading manufacturers of switchgear, complete transformer stations and distribution transformers for medium voltage. More than 2,200 employees in over 100 cities on five continents ensure reliable energy distribution with high-quality products and services. Ormazabal is part of Velatia, family-owned and headquartered in Zamudio, Spain. The headquarters of Ormazabal’s German manufacturing and sales companies in Krefeld is also the headquarters of the Central Europe region. With local know-how and global experience, Ormazabal GmbH offers forward-looking solutions for all aspects of energy distribution. As a project partner for energy suppliers, planners and installers, among others, the provider responds flexibly and pragmatically to individual customer requirements and supports projects from planning to commissioning and maintenance. Ormazabal’s products are used, for example, in the power supply industry, renewable energies, the plastics and automotive industries, airports, railway stations, hospitals and even football stadiums. For more information, please visit http://www.ormazabal.com/de