Today's electricity grid is designed based on a vertically integrated supply model with dispatchable centralized generation and distributed consumption with no generation resources on the distribution network.
Distribution networks tend to be radial with mostly unidirectional power flows and "passive" operation. Their primary role is to deliver energy from the transmission substation to the end users. The design and operation of the distribution grid has not changed much over the past three to four decades.
While distribution operators have always faced challenges from both regulatory bodies and consumers to improve the reliability of electric service delivery while keeping costs in check, new developments such as utility smart grid investments, the advent of electric vehicles, more distributed generation, the aging of utility infrastructures, more demand response and greater capacity of intermittent generation on the grid means a major change in the way distribution operators manage the system.
As a result, the smart grid of the future will need to accommodate more intermittent and decentralized generation, and support bi-directional power flows. Additionally, distribution systems may require standby capacity, which could be called upon whenever the intermittent resources cease to generate power.
DMS offers holistic treatment
Utilities are examining tools to help them address these challenges, and one such tool is a Distribution Management System (DMS). A DMS makes the information from utility network assets available to enterprise operations and business processes. It helps utilities collect, store and analyze data from hundreds of thousands of data points in distribution networks, perform network modeling, simulate power operation, pinpoint faults, preempt outages and participate in energy trading markets.
Reliability and quality of service in terms of minimizing outages, maintaining acceptable voltage and reactive power profiles, reducing outage times and slowing down the growing cost of system operations have been important incentives for distribution operators to consider acquiring a DMS.
Traditionally, distribution operators have relied only on IT information system solutions to manage their distribution business. IT solutions such as geographic information systems, outage management systems, and customer information systems, although important parts of managing an effective distribution operations business, lack the ability to analyze and subsequently operate the distribution system in real time, for optimal performance with respect to reliability and electrical efficiency.
A DMS provides a more holistic view of the entire electric distribution network. With the advent of new, cheaper communications and IP-based networking technologies this holistic and total view will become more important. These technologies are bound to extend the utility information network downstream from the feeder, and eventually all the way to the house meter and in-home control systems on the residential side.
A business case for DMS
There are a number of business factors that can drive a utility's decision to implement a new DMS. For example, Avista recently completed a major DMS initiative and had multiple drivers that made the business case for the project, according to Curt Kirkeby, senior electrical engineer at Avista.
"Avista has a fairly sophisticated outage system based on GIS technology that models the electric network," Kirkeby said. The system has been continuously extended since initial efforts began in 1999.
"This outage management tool is tremendously capable for managing outages and provides detailed statistics. One of the key objectives of reliability is to examine how to impact the fewest customers possible. We can develop a business case by assigning a value to every hour a customer is without power, making a determination what that cost or value is and validating that cost with the customer.
"This system has allowed us to collect complete statistics around our reliability indicators, so we know quite accurately what our current performance is. The goal for the DMS is automatic restoration of more than 80 percent of the outage minutes that customers currently experience," he said.
Another important business driver for utilities is voltage optimization. "From voltage optimization we obtain a constant, ongoing savings," said Kirkeby. "Because the system is constantly receiving measurements, it's not static-it is adjusting voltage regulators and capacitor banks to save system losses and reduce loads, which then frees resources to supply other customers."
Utilities can expect numerous operational efficiencies. "Once an outage condition has been recognized, the DMS performs restoration in two stages: upstream followed by downstream," he said. "Right off the bat we know the exact section of line that has a problem, whereas in the past a crew might have had to drive around for an hour to find where on the circuit that problem might exist. With the DMS and other supporting technologies, we could potentially reduce the trouble investigation to one section that might be only a quarter mile long. We are able save valuable crew time and may also have knowledge beforehand about what kind of fault occurred, so the crew has a better idea of what materials and equipment to take with them to the trouble location."
Providing AMI efficiencies
"An AMI component also provides Avista with an additional level of opportunity with respect to our meters," said Kirkeby. "We may get a customer reporting that the power is out when it's only a breaker in the customer's house, and the customer doesn't have the knowledge to determine the reason for the outage. Frequently we send a crew out to assist assuming a utility problem. With the ability to ping the meter for power status, the service trip to the customer's home can be avoided and we can assist the customer by phone with resetting the breaker, reducing the outage time. Those are very real savings."
As well, there are many additional efficiencies. "You can calculate vehicle miles not travelled, identify carbon emissions not excreted, use a service switch in the meter to turn meters on and off for account opens and closes, and access the meter for on-demand reads to detect a problem with the meter or investigate a theft issue," Kirkeby said.
"Additionally, we can reconcile customer loads with transformer loads to analyze the loss components all the way down to the customer. As a result we have a very good idea of the loss elements on the whole distribution system. Prior to smart grid concepts and the communication options that allow smart grid to happen, utilities were forced to estimate distribution losses.
"You can do research out there, but it says it's anywhere from 2 percent or 3 percent up to 8 percent or 9 percent-nobody really has the exact numbers. Avista wants to understand and calculate the baseline value of the distribution system losses and then apply remedies to reduce them to minimal values. We're going to strive for maximum efficiency savings, optimizing the system for least loss costs."
Effective management of the distribution network will be critical in achieving the goals of a smarter grid. DMS is increasingly becoming a vital part of modern power networks and enabling the development of a smarter grid, as the smart grid will have to incorporate and manage distributed power generation, intermittent sources of renewable energy like wind and solar power, allow consumers to become producers and export their excess power, enable multi-directional power flow from many different sources, and integrate real-time pricing and load management data. With a DMS, utilities can optimize the efficiency and reliability of their power delivery system and the returns from significant smart grid investments.