Smart Grid Telecommunications. Ramon FerrúsЧитать онлайн книгу.
network infrastructures require large investments spread through the territories they serve and are bound to the physical space where they are located. From an intuitive perspective, it would most likely not be efficient to have two competing electricity grids in the same area providing the same service. From the analysis of real practices, the widest accepted reality is that Transmission and Distribution activities are natural monopolies and, as such, are closely regulated.
If technical details are analyzed, the conclusions become evident. Transmission and Distribution parts of the grid are characterized by different aspects leading to the efficiency of a single infrastructure to provide the service. First, the duplication of Transmission or Distribution grids is not affordable in terms of cost, land use, and environmental impact. Second, in the case of the Transmission grid, the unit cost of transmitting electricity (cost of 1 km of line per unit of transmission capacity) declines abruptly with a line's total transmission capacity, involving that a single element performs better than two. Third, the essentiality of the service in a territory, the operation of the network as a whole, the prevention of market control scenarios, and the technical design constraints advocate for this monopoly type of regulation.
However, Transmission and Distribution grids are different among them. Each one has a different impact and complexity within an electric power system and do pose a different burden and risk to the utility operating it. Thus, the way in which they are regulated should be different:
Transmission networks have a huge impact in wholesale markets, and regulation should focus on their proper performance.
Distribution networks are the origin of over 90% of end‐consumers outages, and regulation should bear in mind the quality of supply.
While Transmission infrastructure is relatively standard and can be audited and controlled easily, Distribution grid differs greatly among territories and its assets are widespread. Thus, Distribution requires much more simplified procedures to calculate remuneration (compared to Transmission), typically incentive‐based.
The economic characteristics of Transmission networks are associated to investments. This statement is comprehensive of operation and maintenance costs, as they are proportional to the investment. Relatively speaking, the economic weight of Transmission networks with respect to all activities involved in the electric power system is significantly lower than Generation and Distribution, and it is typically between 5 and 10% of the total cost of electricity.
As with Transmission network, Distribution networks' costs include the investment needed to strengthen the existing grid and build new facilities to expand it. The cost components also include the obvious operation and maintenance activity, energy losses costs, and those of auxiliary activities such as meter reading and billing for network services. It is important to mention that Distribution network charges are generally separated into connection charges and use‐of‐system charges. The former is a single payment when a new connection (or upgrade in the existing connection) is required, and the latter are the periodic payments made by network users to cover the total cost of the regulated service.
All in all, Transmission and Distribution electric utilities have the need and the opportunity to invest heavily in their networks, as long as that is justified, and approved by Regulators. Then, they can translate these investments in long‐term recognized costs that will be part of the service tariffs.
A final note on this cannot miss the point that the emergence of the new developments in power systems (DG/DER/DR‐including Distributed Storage or DS, EVs, Demand‐Side Management [DSM], etc.) is challenging the technical status quo of electricity business structure and may ultimately motivate the appearance of new regulatory models that may adapt better to the new situation. However, present‐day grid evolutionary needs must be addressed within the current scenario. A smart regulatory design and implementation will be required to guide financial resources to support Smart Grids.
1.2.3 Grid Operations
Electric power system management is a complex undertaking covering technical, economic, regulatory, social, business, and environmental factors. The management of a power system combines investment planning and system operation and maintenance to ultimately deliver the electricity supply. These processes have both short‐term and long‐term components across different grid segments.
Investment planning is a process projecting itself anywhere from 2 to 15 or more years. The process involves determining which and when new generation and network facilities are to be installed. Factors taken into account are demand growth forecasts, technical alternatives and costs, budgetary limitations, strategic considerations of generation resources, grid reliability criteria, environmental constraints, etc.
Power system operation and maintenance are performed under the assumption that production and consumption have to be always in balance: a mismatch between supply and demand in a large system cannot happen, as the overall dynamic balance would be compromised and the supply of electricity across a significant amount of the grid potentially lost. At the same time, system parameters, namely, voltage and frequency, must remain within predefined operation thresholds in the short and long terms. Maintenance of power systems is not conceptually different to the practices of any other business: reactive maintenance is needed when an unplanned failure occurs; preventive (proactive) maintenance is planned to minimize future system failures.
Power system operations and investment planning meet in system planning. System planning is part of the grid operations, and its consequence is the identification of the investment needed. System planning, as a process, intends to understand and forecast load location and needs to adapt the grid consequently. System planning considers the generic elements mentioned earlier and considers a short‐ and a long‐term scope. Long term requires a system model and considers load evolution and associated changes needed in the existing system (e.g., new power lines or substations, refurbishment of existing infrastructure: feeders, transmission capacity) along with relevant constraints (e.g., budget) to develop different prospective scenarios and adapt to them. Short‐term planning implies detailed analysis of the existing infrastructure, both Transmission and Distribution segments. Different topological and performance data feed studies to analyze voltage drops (to identify weak points in the grid), sectionalizing options (to minimize outages), conductor adequacy (based on power required), etc. It will ultimately affect the evolution of all system components.
Protection and control are electric power system functions that are transversal to all grid management areas. System operations depend on a combination of automated or semiautomated control and actions requiring direct human intervention. Operations are assisted by electromechanical grid elements and recently enhanced with the support of ICTs:
Protection. This function ensures the safety of the system, its elements, and the people. Protection schemes must act in real time when there is a condition that might cause personal injuries or equipment damage. However, protection cannot avoid disturbances in the system. Faulty conditions (faults) are detected and located based not only on grid voltage and current measurements but also on some other parameters. A fundamental part of the operation of a power system is to quickly detect and clear faults, rapidly and selectively disconnecting faulty equipment and automatically reclosing for supply recovery in case of transient failures.
Control. Power system operators manage their grids from Utility Control Centers (UCCs). Different UCCs exist, dealing with different grid domains (grid segment and/or territory). Most routine operations of a well‐designed system should not require any human intervention; however, a number of manual operations are needed. Power system data are constantly and automatically collected for the required analysis of system performance for planning and contingency analysis.
Producing the power needed in the system is the task for the Generation segment in a traditional electric power system. In traditional monopolistic environments, vertically integrated utilities knew when, where, and how much electricity was going to be needed and scheduling of energy production was relatively easy. More recent market‐based decentralized approaches have increased the complexity of the task for the sake of the system efficiency.