About Us > What We Do > Our Three Critical Roles

Operating the
Power System

Overseeing the day-to-day operation of New England’s power grid is one of three critical roles ISO New England performs in the region.

Balancing Electricity Supply and Demand Every Minute of the Day

Before electricity is delivered to homes and businesses from the power lines on your street, it is generated and transmitted over a high-voltage electric power system that spans thousands of miles across the six states of New England. (Learn about how electricity is transmitted.)

The ISO is like the air traffic controller for the region’s power grid. From our state-of-the-art master control center (MCC) in Holyoke, Massachusetts, the ISO’s certified system operators monitor, dispatch, and direct the flow of electricity across the power grid 24 hours a day, 365 days a year.

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System Operators and Backup Control Center

The ISO’s system operators go through a rigorous and continuous training process and must be certified by the North American Reliability Corporation. In the unlikely event that the master control center is rendered inoperable, fully redundant systems at the backup control center (BCC) enable system operators to continue managing the grid reliably.


Forecasting New England’s Electricity Use

To ensure a reliable supply of electricity, our operators must consider a large number of variables that can at any moment affect the production and flow of power across the grid. These include:

  • The hourly demand for electricity (largely influenced by time of day, year, and weather)
  • The availability of power resources
  • The possible effects of any failures of power system components (generators, transmission lines, circuit breakers, etc.)

ISO staff work around the clock to create a variety of demand, or “load,” forecasts. These short-term forecasts help us decide how many megawatts (MW) of electricity we need for a given week, day, or hour, and help us to manage the grid reliably through cold temperatures in the winter, high temperatures in the summer, and at other times of unusual demand. We continually track weather and monitor power plants for unexpected outages and transmission lines for overloads to update these forecasts. The ISO also creates annual—and even longer-term—forecasts for use in regional system planning.


Dispatching the Power System

To meet the hourly forecast of electricity consumption, ISO control room operators issue electronic or verbal instructions to each of the hundreds of resources—generators, transmission facilities, and other market participants in the region—to start up, shut down, raise or lower generation, modify interchange schedules, etc.

  • The ISO dispatches the power plants that are scheduled through the markets, starting with the plant that submitted the lowest supply offer. At the same time, the ISO schedules the delivery of electricity through the high-voltage transmission lines.
  • Because electricity cannot be efficiently stored and the voltage and frequency must be kept steady, the ISO takes the pulse of the power grid every few seconds and makes minor corrections to make sure sufficient power flows instantaneously to meet customer needs, line voltages are within an acceptable range, and system frequency is very close to 60 hertz (the frequency that must be maintained across the entire Eastern Interconnection).
  • As consumption grows throughout the day, the ISO dispatches the next least-cost plant to serve electricity demand.

Six sub-regional control centers called local control centers (LCCs), operated by transmission companies, assist ISO New England in running the power system. Like the ISO, these facilities are staffed 24 hours a day by operators who monitor the real-time production and flow of electricity. The LCCs monitor the more local aspects of their portion of the electric power grid and take direction from the ISO control room regarding necessary local actions, such as switching a transmission line in and out of service. They also serve as backup to perform certain critical ISO New England functions. The ISO also coordinates its activities with neighboring power system operators to protect the reliability of the interconnected systems.


Maintaining Operating Reserve—the Grid’s “Insurance Policy”

At any moment, a generator, transmission line, circuit breaker, or other element on the power system could fail or go out of service. For example, a generator could trip due to a cooling system problem, or a transmission line could trip after a lightning strike. Power system disturbances like these are known as contingencies. To ensure minute-to-minute reliability of the power system, ISO system operators adhere to mandatory requirements for maintaining an adequate reserve of electricity supply that can be called on to produce electricity should a contingency occur.

Resources designated to provide operating reserves are identified in advance of the operating day. They can include power plants on standby and ready to produce electricity at a moment’s notice—or electricity imported from outside New England. ISO operators closely monitor these resources to ensure that they will be able to generate electricity within the prescribed time frames necessary to keep a constant balance between the supply and demand of electricity on the grid.

Always Ready: Contingency Analyses

The ISO performs a contingency analysis using special software every few minutes to simulate the loss of each system component (there are thousands!) and determine which transmission line or generator losses would have the largest adverse impacts on the system in real-time and future hours. Once these worst-case scenarios are calculated, a plan is prepared to change the flow of power in the system to prevent a power interruption or to prevent an isolated event from triggering a cascading, systemwide loss of power—in other words, a regional blackout—due to the highly interconnected nature of the grid.

ISO New England maintains two categories of reserves: resources that can provide energy within 10 minutes and resources that can provide energy within 30 minutes. Typically, the ISO maintains an operating reserve of between 1,560 MW and 2,250 MWin 10-minute reserve, plus an additional 625 MW or so in 30-minute reserve. (Read about the organizations that set operating reserve and other reliability rules and standards followed by the ISO.)

A variety of circumstances can jeopardize the amount of required operating reserve available on the system, such as having an unusual number of power plants out of service due to mechanical problems or experiencing unexpected high demand due to extreme hot or cold weather. To respond to such conditions, ISO New England has special operating procedures to keep the power system operating reliably when reserves run low. Steps can include:

  • Limiting exports to neighboring grids if power supplies are tight within New England
  • Asking consumers to conserve electricity when demand is very high or when the system is stressed

The current status of the grid—including whether any special procedures have been implemented—can always be seen on the Current Power System Status page or in ISO Express.


Coordinating Transmission and Generation Outages

Another responsibility for the ISO related to grid operation is to coordinate the schedule for thousands of transmission-line and power-plant repair or maintenance outages to ensure these outages do not compromise power system reliability.

In addition to measuring the impact of proposed outages on reliability, we also gauge the probable economic effects of these outages and disseminate information on planned outages to market participants. Inadequate transmission capacity in an area of the grid may prevent the least-cost electricity from being transmitted to meet demand in that area. This is called a congestion cost and is a component of the price of wholesale electricity. For example, between 2005 and 2016, the ISO rescheduled 106 major outages, preventing an estimated $210.5 million dollars in congestion costs to New England consumers.

The ISO continues to work with market participants to improve the timely submittal and coordination of planned outages and has made significant progress over the years.

Read the ISO’s latest Transmission Equipment Outage Coordination Report on the Transmission Outage Scheduling page for details.

The ISO’s Other Critical Roles

To be reliable in the short term, the power system must have enough power plants producing electricity, plants in reserve, and plants on line that provide services to keep system voltages and frequency in balance. To be reliable over the longer term, these resources and the transmission lines that make up the power system must adapt to keep pace with changing consumer demand for electric energy, retiring plants, and the addition of new resources and technologies. The products, services, and infrastructure needed to maintain reliability are procured and developed through our two other functions:

To learn more about operating the grid, log into ISO-TEN to view the ISO’s training module, Introduction to ISO New England System Operations.

Key Grid and Market Stats