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The vast number of small, distributed power producers is adversely impacting power quality and increasing the requirements distribution grid operators must meet. Identifying, locating and eliminating disturbances and faults as well as flexible, quick balancing of power production and load consumption will only be possible if specialized hardware and software work together optimally.
Controlling distributed power generation systems
The steadily growing share of small power producers in the energy mix affects power quality. Utilities and grid operators have to react in order to optimize the grids.
Power grids are growing steadily more complex: As the number of small, distributed power producers rises, the number of tasks that grid operators have to master to maintain grid stability is also growing. Siemens supports the work of distribution system operators with integrated solutions. Networked devices and high-performance software enable rapid, predictive action to prevent disturbances and faults before they arise.
Grids are accommodating a growing volume of power feed-in from numerous small, distributed power producing facilities, which entails widely varying load and feed-in conditions with significant fluctuations in operating voltage. At the same time, the security of power supply and compliance with the regulations arising from codes and standards must be ensured, if possible without having to invest in costly grid expansions. In short, the challenges facing distribution system operators are growing on an enormous scale, and can only be mastered with intelligent solutions.
To enable operators to be prepared for these and future requirements, Siemens has developed an intelligent semi-distributed design concept for managing voltage and capacity in power distribution grids. It's based on a regional controller and utilizes various approaches to voltage control depending on the given structures and conditions on site and in the field. In addition, various options can be combined to create an optimum, custom-fitted solution designed to achieve maximum efficiency with the existing grid arrangement.
Whether for primary transformer substations or local distribution stations, modern remote-control systems and components such as voltage regulators at the medium-voltage level, controlled distribution grid transformers at the low-voltage level, or intelligent field devices, the solutions from Siemens ensure efficient operation of the entire medium-voltage grid as well as regional and local voltage and grid stability right down into the low-voltage range.
Key benefits of this semi-distributed design concept:
Due to the growing volume of electricity generated by distributed power producers, grid operators in the future will have to monitor harmonic loads more closely (for example because of potentially defective inverters). Such effects can negatively impact nearby industrial operations, and even television reception and computers in residential areas. Power grid regulatory authorities in many countries already demand compliance with EN 50160 as key performance indicators for power distribution systems.
For these and many other tasks, the SICAM product family offers a broad range of devices customized to serve various grid situations: from power measuring devices such as the SICAM P50 to the SICAM P850 as a Class-A measuring instrument in accordance with EN 50160. For integrating important components, SICAM Q100 also delivers additional information for further evaluation. Siemens has also developed the SICAM PQS Power Quality System as an add-on to the SICAM PAS to provide efficient analysis enabling automatic pre-processing of signals. As a result, the event monitor, for example, only displays critical grid situations and hides all irrelevant data.
An integrated solution for power quality management – with integrated benefits
Managing distributed power producers is necessary in order to avoid grid overload situations, prevent voltage problems and maintain balance between power generation and consumption, i.e. demand. One possible means of doing so is by regulating the reactive power via access to the distributed producers. Alternatively, capacitor banks can optimize the power factor at the critical point, and thereby optimally utilizing existing cables and overhead lines.
In many countries, distributed power producers can even be disconnected from the grid in critical situations. In order to prevent such conditions from arising at all, however, energy storage systems can regulate the balance between power generation and load demand. And consumers themselves can also lend their support for balancing through demand management by coordinating power surplus on the one hand with peak- and high-demand periods on the other.
Support for meeting and mastering these challenging tasks is provided by the Grid Optimizer software of Spectrum Power™ that enables coordinated use of distributed power producers, energy storage systems, capacitor banks and other components for load compensation and balancing. This includes the remote terminal unit SICAM A8000 that links with distributed producers via standardized inputs and outputs. The Grid Optimizer software can also control the charging and discharging of battery storage systems using real-time information from the grid, supplied via SICAM P50 or P850 units. This software is also capable of controlling industrial electrical load demand, as many processes allow electrical demand to be disconnected, or load consumption to be increased when surplus power is available.
Distributing various measuring devices throughout the entire distribution grid is a question of time and money. Strategically critical and important local distribution substations are the first locations to be equipped in order to optimize such deployment from an economic standpoint. Real-time state estimation performs an important function in this process, enabling that portion of grid substations that are not equipped with measuring equipment to be mapped and considered.
Real-time state estimation can be calculated either centrally or on a distributed basis, performed by the Spectrum Power™ Advanced Distribution Management System (ADMS). This enables advance detection of critical grid situations. This also provides grid planning engineers with detailed insight into recurring load demand histories and up-to-date load flow diagrams as well as into voltage level monitoring.
The expanding use of renewable energy sources means that the share of power generated by photovoltaic (PV) installations is also growing, creating new sources for disturbances in distribution grids. An innovative method of analyzing existing data allows targeted identification, location and elimination of such disturbances and faults, thus improving grid stability.
These disturbances and faults are caused by incorrect parameters at the inverters for voltage and reactor power behavior. In systems of certain threshold sizes, the grid operator can extract and read these parameters or even change them remotely from outside if the systems are very large. In smaller systems, parameterization is performed at the manufacturing plant or subsequent to malfunctions or faults. In general, older systems not equipped with this function do not need to be backfitted.
For such cases, measured values taken from any random point in time in 1-second resolution can be used to validate parameters of the inverter characteristic curves. These data are compared against the baseline points of the target characteristic lines. The graphical representation of these values provides a map of the real situation in the grid, revealing disturbance and fault situations based on seemingly arbitrarily distributed points that deviate from the ideal state. Every deviating point corresponds to a poorly set inverter in the grid, which in sum total can cause disturbances and faults in the grid. Adjustment of the parameters in the inverters can eliminate the disturbances and faults.
Products and solutions from Siemens enable easy and reliable integration and management of distributed power generating systems in grids and processes. Listed below are just some of the reference projects.
Optimizing the control of voltage and battery storage systems as well as demand response
Preventing voltage fluctuations that exceed the required voltage level range that arise from integrating renewable energy sources
Rapid implementation ensures optimum grid operation and cost reduction
Photovoltaic technology replaces diesel generators
Lower CO₂ emissions
Lithium-ion battery storage systems optimize use of PV installations
Cost-effective operation of a real network as a microgrid
Hybrid structure with wind power, PV, heat and power cogeneration unit, and plant-oil-fired generator
Supply of power to the superimposed grid