How the IntelliGrid Architecture Comes into Play

In order to best understand the scope of the problem and application domains that a comprehensive utility communications, command, and control architecture must deal with, here is a fictional but realistic future scenario of how a fully deployed system might operate. This vision of the future of power system operations will serve as a basis for describing the technical approach to be used in defining the requirements for the IntelliGrid Architecture, formerly known as the Integrated Energy and Communications Systems Architecture or IECSA.

This scenario is designed to illustrate how use of the IntelliGrid Architecture can improve the reliability and performance of the overall system with communications and coordination, all the way from power generation to end-user facilities. It is only one of many scenarios where the systems architecture will support new applications that were previously not possible. Overall, the implementation can result in significantly improved reliability and power quality, while optimizing operation of the system at the same time.

The Scenario

This afternoon around 15:00 CDT near Nashville, Tenn, heavy thunderstorms roll into the area. The temperature is 99° and the humidity is about the same: a new peak load record will be set today. High winds, heavy downpours, and significant lightning accompany the storms.

At 15:12:10 CDT, lightning strikes a tower on the Tennessee Valley Authority 500-kV Roane-Wilson line, the major line serving Nashville from the East, and causes a flashover. This is reported in real time via the National Lightning Detection Network (NLDN) and reported automatically on the operator's supervisory control and data acquisition (SCADA) display.

The flashover results in the failure of one of the line insulator strings-a permanent fault. The ensuing fault results in breakers opening at the Roane and Wilson stations. Due to a protective device configuration problem, the 1100-MW generating plant at Watts-Bar trips off-line.

At 15:12:40 after unsuccessful re-close attempts, the breakers lock out due to the permanent fault.At 15:12:45, the automatic generation control for the area starts responding to a deficit of generation in the Nashville area caused by the line outage and generator trip. Signals are automatically sent to other generators in the area using the newly implemented IntelliGrid Architecture to increase local generation.

At 15:13:00, the Emergency Control System (ECS) module of the IntelliGrid Architecture determines that there is not enough generation or line capacity to meet the generation deficit. The ECS evaluates the situation and decides that a combination of line reconfiguration, power flow controller operation, load reduction, and dispatch of distributed generation resources in the area will make up the deficit. The system updates prices for the next hour for customers on hourly real-time pricing rate structures, sends interrupt signals to selected interruptible rate customers in the affected area, and initiates residential load control by sending signals to shut down water heaters and other non-essential loads for that time of day.

As generation starts to come on-line and load is reduced, several flexible AC transmission system (FACTS) controllers in the area are also commanded to divert power flow onto the TVA 161-kV lines to help make up the deficit. On-line power flow, stability, and security analysis applications re-calculate the optimum FACTS configuration.

In an industrial park in the Nashville area, a large, automated plastic bag manufacturing plant on a real-time rate receives the next hour's prices, which are very high due to the line and generator outage. Their energy management system decides to shut down the plant to save money. Nearby, a semiconductor manufacturing firm benefits from a temporary reconfiguration of protective devices in the area. When the local ECS determined that a storm was in the area (from the NLDN data), the re-closers' instantaneous trip settings were temporarily restrained on selected feeders serving sensitive loads in order to minimize momentary interruptions and multiple sags due to multiple re-close attempts. A few more fuses were sacrificed in residential areas to prevent the storm from disrupting critical industrial loads during the day.

An Internet service provider in the affected area is on a feeder with distributed generation resources sufficient to meet the entire load in that area. When the ECS dispatched the generation, the local substation controller decides to temporarily "island" itself from the main utility grid to eliminate the impact of voltage sags from the transmission system.

By 15:15, the load/generation imbalance has been fully satisfied, and a new, stable system configuration has been achieved. As the storm moves through the area, small, local configuration optimizations are performed.

The storm dissipates by 15:45, and as local ECS controllers sense this through input from various distributed measurement devices, they begin restoring protective device settings to normal. As work crews complete repairs on the transmission line a few hours later and put it back in service and the Watts-Bar generator comes back on-line, real-time prices are adjusted accordingly; generation is re-dispatched; line configurations and FACTS controllers revert to their normal, optimal configurations; and islanded systems are re-synched to the grid.

By the next morning, several applications with access to the ECS database have automatically prepared reports on how the system performed, the total cost of the storm including incremental generation costs, repair costs, etc. Power quality and reliability performance reports have been prepared for engineering and marketing personnel. Any system anomalies encountered during the storm have been automatically analyzed, and a maintenance plan has been prepared and e-mailed to appropriate personnel.

The IntelliGrid Architecture has prevented a wide area outage due to the generation deficit, has optimized the configuration of local distribution systems to deal with the storm, and has minimized disruptions that specific load centers are sensitive to.

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