Key Results

  • new generation of groundbreaking algorithms
  • prototypes demonstrated on Pan-European systems
  • the way for future research and for industrialization


CONTEXT
The European Transmission Network (ETN) has been developed and operated up to around the year 2000 under the so-called UCPTE (now ENTSO-E) rules. At that time, utilities were usually national monopolies vertically integrated from generation down to the retail distribution. Each utility had the responsibility of balancing the power delivered to their clients by means of their own generation fleet. The interconnection of the national networks basically had the sole role of sharing generation reserve in case of tripping of a generating unit somewhere in the ETN. The savings in generation capacity and the possibility to install larger, more efficient units in the smaller utilities paid for the investment of the interconnection lines. The consequences of the UCPTE rules at the level of the operation of the ETN were such:
  • The flows on the interconnectors were normally low or zero.
  • In case of major disturbances, the interconnections were intentionally tripped in order to avoid the extension of a possible blackout.
  • The N-1 network security was managed at national level.
  • Very few data exchange between countries was needed.


Today the paradigm of the ETN has changed:

  • The liberalization of the electricity market and the implementation of the IEM (Internal Electricity Market) make use of the total available cross border transfer capacity and call for reinforcement of the transmission network. But new investments are late.
  • The integration of a large amount of intermittent renewables, either dispersed in the distribution system or remotely located far away from the load centers call for network reinforcement (possibly a supergrid), cross border load balancing, much more sophisticated grid operation and operation planning, and smarter distribution grids.
  • New technologies in the domains of ICT and power electronics are available to help the ETN to become smarter. This calls for new models for generating units, wind farms, FACTS and electrical interface of load with the system and is a major difficulty managed in this project.
  • For political and security of supply reasons, further extensions of the ETN are planned (Turkey) or contemplated (Russia, Mediterranean ring) leading to the most extended interconnected system in the world.


The Pegase Project
As a consequence, the organization of the operation of the ETN must adapt and become much more integrated and smart. The way the ETN operation was decoupled into national grids is far away. The ETN shall be, and already is, operated much closer to its physical limits. The awareness of the state of the system by the operator must be much more accurate and extended to all system wide phenomena putting the ETN possibly at risk.
  • The PEGASE project aimed at removing algorithmic barriers related to the monitoring, simulation and optimization of very large power systems. The project has produced powerful algorithms and fullscale prototypes validated on the European Transmission Network to enhance the cooperation among transmission system operators for the real time control and operational planning of the system.



The four-year R&D project ending June 2012 has developed new powerful algorithms and fullscale prototypes able to run the whole ETN model for state estimation, dynamic security analysis, optimization and real time dispatcher training. It was funded by the 7th Framework Program of the European Union and implemented by a consortium composed of 22 partners which included Transmission System Operators, expert companies and leading research centres. The project demonstrated the absolute need of coordination beyond the borders between TSOs when operating the ETN and the actual implementation of this coordination is to be agreed between the TSOs as exemplified by the regional coordination centres already set up.

DISCLAIMER
The PEGASE project focused on removing algorithmic barriers to enable real time control and operational planning of the European Transmission System.

1. Non technical barriers were not the focus of this project. They will have to be addressed to enable the deployment of the proposed solutions that proved technically feasible.

2. No real set of data of the ETN were used in the PEGASE project but instead realistic data representative of the ETN. The objective was indeed to test the adequacy and performances of the prototypes and not to carry out a study on the European system.

3. Data management issues were not the main focus of the PEGASE project and they will be addressed in a dedicated R&D project: iTesla.


3 ACHIEVEMENTS
SMART TOOLS FOR TRANSMISSION GRID

The PEGASE project succeeded in developing smart tools for managing the transmission grid.
The project achievements can be summarized as follows:






4 TOPICS
In order to ensure an efficient and safe operation of the power system, various computational tools are used by the TSOs. Most of those tools must adapt to the needs of a more integrated operation of the ETN. In particular, the model of the system used at the national level must be extended possibly to the whole ETN and updated in real time.

STATE ESTIMATION
A SINGLE ENTRY POINT OF ALL ON-LINE GRID APPLICATIONS AT THE CONTROL CENTRE
State Estimation (SE) determines the most likely state of a power system from a set of real time data captured at the substations. Today, the SE is run independently by each TSO, on its own grid. To accept the new challenges of the ETN, a fully synchronized global SE must be implemented.
The PEGASE project has determined the best architecture of a two-step hierarchical SE prototype running the entire ETN and maximizing the accuracy and robustness of the procedure when minimizing the exchanges of data.
But a sound architecture of the SE will not be enough to master the complexity of the ETN. That is why the use of new ICTs has been considered:
  • Synchronized Phasor Measurement Units (PMU) have been optimally placed in the grid ;
  • PMUs have been introduced in the two-step SE algorithm using the developed Phasor Data Concentrator (PDC) prototype. Results confirm their usefulness in terms of accuracy and robustness.
  • A local SE at the substation level, including topology estimation and using IED’s data, has notably improved the global SE procedure. All the developed algorithms have been tested on pan-European systems.
STEADY STATE OPTIMIZATION
SIMULATION OF OPERATIONAL POLICIES
Anticipating the power system state is an essential step of the operational process. Steady State Optimization aims at creating these anticipated states of the system. Today, Each TSO is operating its own network close to the limits with more and more corrective actions in a context of higher uncertainties due to renewable energy sources and increased interactions between neighbouring networks. An optimization of the whole ETN must be considered. The PEGASE project produced several conclusions and achievements:
  • A Security Contrained OPF (SCOPF) prototype has been created, based on constraints filtering and network reduction methods. A full size prototype able to run huge systems with a huge amount of constraints (typically 10000 nodes and 30000 constraints) has been set up and tested on the ETN;
  • A discrete variable prototype able to manage an ETN model with large number of discrete variables modelling the discrete behaviour of equipment has been developed considering some approximations;
  • New formulations of the actual operating practices, favouring corrective actions against preventive actions, have been proposed;
  • A “Worst-case” approach has been developed as a screening method to anticipate possible unsecure states of the system.


TIME DOMAIN SIMULATION
FOR SECURITY ANALYSIS OF THE SYSTEM As a result of the change of paradigm, the ETN is operated close to its stability limits. Moreover, it has been shown that system wide detrimental phenomena may lead to the total blackout of the system.
The terms of references of PEGASE project concerning dynamic simulation were far reaching:
  • To detect any unstable phenomenon somewhere in the ETN, a detailed electromechanical model of the whole ETN had to be used, the size of such model being at least 125000 state variables;
  • The dynamic simulation must be fast enough to replace the classical online (N-1) security assessment based on a static model.
An impressive research effort has been delivered. Different approaches were investigated: Fine grain parallelization, advanced linear algebra, domain decomposition methods, multirate algorithms, localization techniques, etc. World-class results were obtained: A relevant combination of the research outcomes allowed a speed up of 10 to be reached on the detailed ETN model.
For online security assessment, a specific integration algorithm has been developed having the capability to filter the faster stable phenomena and offering a good trade off between speed and accuracy.
A full accuracy prototype and a simplified simulation prototype have been produced and successfully tested on systems of up to 140000 state variables.
DISPATCHER TRAINING SIMULATOR
TRAIN OPERATORS ON CROSS BORDER COOPERATION AND CRITICAL SCENARIOS
The role of the dispatchers is central in the operation of the European Transmission Network (ETN) and is one of the major components of the security of the overall system. It is crucial to train system operators on multilateral cross border operational issues and events that might lead to large-scale blackouts if not timely tackled.
The present state of the art of DTS consists in using a replica of a single control centre linked to a quasi steady state power system model. This is no longer satisfactory.
The PEGASE prototype has developed a real time simulation engine meeting the requirements of the project: capable of simulating the entire ETN with high fidelity, whatever the electromechanical behaviour of the system, up to the complete blackout and the subsequent restoration. This simulation engine capitalizes on the deep knowledge of the algorithms gained along the project.
A DTS prototype made of the ETN simulation engine connected to a replica of the control centre of a consortium member and to a generic operator station has been built and tested on realistic scenarios.
SUMMARY TABLE