by Jeff Meyers, Telvent.
Not everyone agrees on a precise definition of the smart grid, but most agree the modern grid will become increasingly complex.
As new kinds of loads, sources and equipment are implemented, the nature of the distribution network might evolve from a radial, one-way commodity delivery system to a bidirectional one. As the modern grid grows in sophistication, the need to plan, engineer and operate the network more effectively is critical. Enter advanced distribution management systems (ADMSs). Innovations in distribution management systems (DMSs) are helping address network complexity and making the smarter grid a reality.
A Revolution in DMS
DMS isn't new. Some utilities have used computers to model their networks for nearly four decades using load-flow algorithms to calculate voltages and power flows at nodes throughout the network. More recently, say, for the past 25 years, supervisory control and data acquisition (SCADA) systems have monitored and controlled the grid at key locations such as substations in real time. More recently, DMS combined the two ideas, solving the network model with using a load flow while accessing key real-time data points to enhance the picture of the grid.
As good as they were, first-generation DMSs can't cope with the requirements of a smarter grid. To safely and reliably operate, the modern grid needs a brain with capacity and functionality.
The Foundation of ADMS
At the core of the ADMS is the ability to define the network model precisely and to process an unbalanced load-flow algorithm based on that model with telemetered data taken from the network:
- The network model. The ADMS must be able to represent all aspects of the distribution network, including various conductor types, transformers, manual and motorized switches, fuses and other permanent and temporary devices in distribution system operations.
- The dynamic data. To enable functioning of the ADMS load-flow algorithm, data must be telemetered from the distribution network. That data generally is made available through SCADA systems and their associated telemetry, through AMI networks and from the outage management system (OMS).
- The unbalanced load-flow algorithm. The ADMS must have a fast load-flow algorithm that can solve unbalanced distribution networks based on data telemetered from the field.
- The state estimator. Power system engineers use the term "state estimation" to mean the ability to monitor certain points in the network for things such as voltage and current and solve for those parameters at other, nontelemetered points of interest.
Visualization of ADMS Results
With a complex network model, significant quantities of telemetered and calculated data and the wide variety of ADMS users' providing visualization of ADMS results is critical. An ADMS should be able to display network data in a geographic view (e.g., maps), a schematic view and in single-line diagrams. Furthermore, an end user easily should be able to manage the level of information displayed.
ADMS Analytical Functionality
The ADMS has functionality that supports several functional areas:
- Operations planning and analysis, loss minimization. One of the greatest features of ADMS is its ability to continually run real-time analysis, identify problems and suggest approaches to better balance the load. It also can identify other potential problems, as well as likely solutions.
- Supporting outage management activities. The ADMS provides analytical support to ensure outage causes are identified and resolved quickly. It also has strong functionality around fault location, identification and service restoration (FLISR). The FLISR functionality that already exists at most utilities through an OMS is enhanced with the ADMS's ability to locate faults based on telemetry and analysis and to provide ranked switching options to a dispatcher (e.g., prioritization based on connected load and connected customers).
- Advanced switch planning. Because the ADMS maintains information about the switched state of the network, it facilitates and automates the creation of switching orders. ADMS can compute switching configurations and offer options to the system operator, supporting smarter network configuration.
Demand response is a key function that drives utilities to smart grid programs and ADMS software. Some demand response actions depend on customers' reacting on their own, yet in other instances utilities and regulators ask consumers to change their electricity consumption patterns when supply is short. Regulators also can create rate structures that encourage similar behavior. Because these approaches do not provide sufficient reduction, the ADMS can help prioritize demand response options. In general, the available options fit into three categories, which are listed in order of lowest to highest customer impact:
- 1. Conservation voltage reduction (CVR), also known as distribution system demand response (DSDR). This functionality uses volt/VAR management functionality to decrease demand through reduced voltage on the distribution network. The voltage reduction, usually between 3 and 7 percent, reduces the power delivered by a similar amount, all without customer awareness. The surgical use of DSDR and its lack of customer impact is often the critical reason to implement an ADMS.
- 2. Direct load control. Many utilities have implemented some form of direct load demand response, generally through radio-controlled devices on water heaters, air conditioners and pool pumps. Using this approach, utilities can turn off these devices for a short time (perhaps 15-20 minutes) to reduce demand on the distribution network. Direct load control will continue to increase in complexity with the evolution of home-area network (HAN) technology and the continued rollout of advanced metering infrastructure (AMI) systems. The ADMS can help analyze impact and optimize feeder configuration during a demand response event, making direct load control much more effective.
- 3. Load interruption/islanding. When other demand response options fail, utilities disconnect some demand to maintain the ability to serve the rest. Once again, the ADMS recommends and prioritizes options for utility dispatchers to enable decision-making in situations where it is unavoidable.
As the smart grid develops, supply assets have diversified to include distributed energy resources (DER) such as solar and wind and fossil-based microgeneration. These new sources can change more than the carbon footprint of the utility; they also alter the generation dispatch paradigm.
ADMS can help maintain the balance needed to operate a diverse supply reliably in the face of dynamic changes in demand and the topology of the distribution network.
Because utilities use a forward look in planning their distribution networks, the ADMS must provide functionality to enable planning and budgeting for maintenance of reliability and quality of service. Advanced planning starts with demand forecasts for the time frames required.
A Smart Grid-Era Tool
ADMS is an indispensable tool of the smart grid era and provides critical functionality to help utilities manage resources and operate their networks efficiently and reliably. As new concerns and challenges emerge, ADMS will evolve and adapt to meet the industry's changing needs.
Instead of the need to model sparse, relatively static, balanced transmission networks, today's ADMS technology must model radial, unbalanced distribution networks with frequently changing topologies and demand profiles. An ADMS must deal with the evolving use of electricity, support changing consumer habits and new electricity-powered devices such as battery-powered vehicles and accommodate new distributed sources--all while operating within regulatory norms for voltage levels.
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