Maintaining Power Supply

Keeping the Lights On

Among the actions taken by ISO New England and the electric companies are:

• Preventive maintenance on power plants to help ensure that generating capacity in New England is at maximum availability, especially through the summer’s peak load season.
• Conducting thorough inspections and preventive maintenance work on transmission lines to assure maximum power transfers.
• Emphasizing to all customers the benefits of energy conservation, particularly at times of peak electric demand.
• Working closely with neighboring power systems (in New York, Quebec and New Brunswick) to augment ISO New England’s ability to import emergency power when needed.
• Working with independent power producers to ensure that their power plants operate at maximum capacity if needed.

To address fluctuations in supply and demand, ISO New England has specific procedures that are implemented if the demand for electricity exceeds operable limits. Called Operating Procedure No. 4, or OP 4, it is a standard part of the capacity management process and includes 16 incremental steps aimed at utilizing additional power generation and conserving or curtailing power consumption. These steps, which are not necessarily followed in order, include operating generating units at maximum levels, purchasing emergency power from neighboring power pools, curtailing power as previously arranged with certain customers, implementing voltage reductions and seeking voluntary public curtailment. OP 4 is implemented by ISO New England routinely to balance supply and demand.

In extreme situations–during a severe generating shortage or the loss of a major transmission line—electric power could be cut off to large blocks of customers to protect the system. This is known as load shedding. Load shedding is implemented only in extreme situations, and usually only after ISO New England and the electric companies have pursued all other available actions. Depending on the situation, load shedding could be immediate, with no prior actions taken. And electric companies may temporarily not be able to keep power flowing to essential facilities.

Another step that could be taken is the rolling blackout. In this procedure, a limited number of electrical circuits in an electric company’s service territory are disconnected, temporarily interrupting service to blocks of customers for periods of time specified by individual utility circuit rotation plans, usually no more than a few hours. After the specified time period, if electric demand still exceeds available capacity, a second group of customers is de-energized for the same time period and power is restored to the first group. Under this plan, power outages are controlled so that their impact is minimized. Additionally, electric companies would attempt to maintain power to specific portions of larger cities served by networked circuits, as well as to facilities such as hospitals, large airports and waste treatment plants. When possible, advance notice of rolling blackouts would be given to affected large customers and the public. However, this may not always be feasible.

Public Notice

ISO New England and New England’s electric companies have communications programs in place to provide information and capacity updates. Using "Energy Advisories," ISO New England and the electric companies will notify customers of conditions that could lead to interruptions in electrical service.

• A "Conservation Day" will be declared the day before unhealthy air quality conditions are anticipated in all or parts of New England and ISO New England projects a high demand for electricity. Customers are encouraged to consider reducing electricity usage.
• A "Power Caution" (also known as “Action 1”) will be declared when there is sufficient power to meet the needs of customers, but electricity reserves are lower than normal. Any maintenance activities that might jeopardize the integrity of the on-line generation or transmission facilities will be curtailed. No advisory will be issued to the media and no customer action is necessary.
• A "Power Watch" will be issued at "Action 9" of Operating Procedure No. 4 as a public notice that additional steps to manage capacity could affect the public and that customers should reduce unnecessary power usage.
• A "Power Warning" will be issued at "Action 15" of Operating Procedure No. 4 as a public notice that immediate reduction in power usage is necessary to avert overload of the electrical system.

In addition, ISO New England’s Web site (www.iso-ne.com) provides the current status of the capacity situation for New England.

Whenever possible, electric companies will attempt to provide advance public notice of potential outages through radio and television news reports.