The capacity of distribution grids is coming under strain with the increasing numbers of small and fluctuating distributed generators feeding into voltage levels below 132kV [Engerati- Smarter Distribution - How To Increase The Capacity Of Distribution Grids To Host Distributed Generation (Part 1)]
In conjunction with grid operators and academia in Germany, ABB has developed several innovative solutions to operate and control distribution grids with high shares of distributed generation. Some of these are described in this guest editorial by ABB’s Britta Buchholz.
Tools to handle increasing complexity
In the past, it was easy to calculate load flows and voltage levels in a distribution system where power was distributed from higher to lower voltage levels. Nowadays, the grid collects and distributes energy at the same voltage level, making calculations more complex. To determine if a generator can be connected without violating limits, software tools are becoming more important for all voltage levels.
One such tool, NEPLAN, is being further developed so that planners can quickly react to requests from customers to connect their generators to the grid. This would help postpone or even avoid investments in grid extension by using the existing infrastructure to its maximum. However, as the infrastructure reaches its limits, asset reliability and availability become even more critical. In addition regulators are demanding flat maintenance spending despite grid extensions.
Another tool, ABB’s Asset Health Center, helps grid operators understand the risk of failure in each of their critical distribution assets, avoid asset failures and at the same time minimize their maintenance expenses.
Increasing grid capacity in Rhineland Palatinate
In 2011, RWE Deutschland AG demonstrated in an award-winning project how an active voltage regulator, the PCS100 AVR, based on ABB power electronics, could stabilize voltage levels in the 20kV grid and at 20kV/0.4kV transformer stations. By decoupling fluctuations at voltage levels of 110kV, 20kV and 0.4kV, the capacity of the grid to host distributed generation was increased significantly, which in turn generated significant cost savings for the grid operator mainly at the 20kV level. Between 2010 and 2013, ABB successfully implemented a total of 10 PCS100 AVRs in 20kV/0.4kV transformer stations.
The project teams concluded that the typical requirements of a distribution system operator regarding voltage regulation at 110kV/20kV and 20kV/0.4kV transformer stations are lower than those of industrial applications and can be met with the more economical solution of an on-load tap changer. The Power Engineering Society of the German Association for Electrical, Electronic and Information Technologies e.V. (VDE-ETG) recommends distribution voltage regulation as an economically smart asset.
Based on these conclusions, ABB developed a voltage-controlled distribution transformer known as Smart-R Trafo to match the requirements of distribution system operators. It is based on an economic on-load tap changer that changes voltage in five steps and provides adequate power quality for distribution grids. Smart-R Trafo is expected to become a standard asset for distribution grid operators in Germany and other markets.
Monitoring and control in Bavaria
The high penetration of distributed generation puts increased pressure on maintaining or even increasing reliability and availability, which in turn affects outage time. To optimize assets and reinforcements, information on the measured load – rather than assuming an unrealistic maximum load or making calculations based on the worst-case scenario – becomes even more important. To address these requirements and further embed voltage regulation in a distribution automation offering, ABB developed a new set of solutions as part of what is known as the RiesLing project (In partnership with Netze BW, EnBW ODR AG and T-Systems).
The first, FIONA, is a remote monitoring and control unit for intelligent secondary substations and provides enough information about the 20kV/0.4kV transformer with only a few measurements. Added to this is the PCS100 AVR with wide-area voltage regulation so that the voltage measured at distributed points is kept within the allowed bandwidth.
New predictive operation features were developed and introduced into the network control system to predict in advance congestion on the 20kV level. These features provide the flexibility to change topologies or allow customers to respond by adapting their consumption behaviour in the future.
Improving asset management
Energy market liberalization and the introduction of incentive regulation have increased the pressure on system operators to reduce their costs while ensuring a high level of service reliability. This means shifting the focus from purely technical issues to technical and economical ones. To achieve this balance, a maintenance plan that fits the used assets as well as the network operation is essential.
ABB’s asset management tool, NEPLAN Maintenance, is approved software for establishing maintenance plans, for example, reliability-centered maintenance as well as long-term asset simulations. A budgeting evaluation tool is available that calculates the costs for various maintenance strategies. Distribution systems play a major role in the ongoing transformation of energy systems. These solutions developed by ABB together with German grid operators and academia support grid operators by technically and economically improving their already existing installations. In the near future further automated (predefined) functions will be able to control primary devices to optimize grid operation.
This article were prepared by Britta Buchholz, Martin Maximini, Adam Slupinski and Leyla Asgarieh from ABB Power Systems Consulting in Mannheim, Germany.