Operating Procedures and Guidelines
ISO New England has detailed operating procedures and guidelines that govern the day-to-day operation of the bulk power system. At its Control Center in Holyoke, Massachusetts, operators monitor the "real-time" generation and flow of electricity across the region's interstate high-voltage transmission system 24 hours a day, 365 days a year.
ISO New England uses both verbal and electronic communications to provide centrally located, real-time direction on the electrical output of each of its 300-plus resources. ISO New England also coordinates maintenance activities of the generators and the transmission system to ensure that the flow of electricity is not disrupted by a planned or unexpected outage of a facility.
To assist ISO New England in operating the New England bulk power system, there are five sub-regional control centers, called Local Control Centers (LCC) operated by transmission companies. Like ISO New England, these facilities are staffed 24 hours a day by operators who monitor the real-time production and flow of electricity. The LCCs work in conjunction with the ISO to ensure reliable transmission operations within their sub-regions. They also serve as backup to perform certain critical ISO New England functions. The ISO also coordinates its activities with neighboring bulk power system operators to protect the reliability of the interconnected systems.
To ensure minute-to-minute reliability of the bulk power system, there are requirements for maintaining an adequate reserve of electricity supply, commonly referred to as the "operating reserve." This means that the operators simultaneously ensure that there is enough electricity to meet the real-time demand of the New England region and maintain an adequate reserve of resources to be called upon to replace any generating source or transmission line that unexpectedly goes out of service. Electricity is generated on demand since it cannot be stored. Once power is generated, it must flow to a source. So operating reserves can be defined as a specific number of megawatts that could be called upon to generate at any given time.
ISO New England maintains an operating reserve to provide the capability to replace within ten minutes the sudden loss of energy production from the largest source of power and to restore within 30 minutes the ability to withstand a subsequent loss of the second largest source of power.
Typically, the ISO maintains an operating reserve margin of about 1,800 MW. Resources designated to provide operating reserve are identified in advance of the operating day, and the ISO New England 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.
Due to a variety of circumstances, there are times when the required operating reserve on the system is jeopardized. Circumstances could include 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 that address a variety of such contingencies. These procedures were developed during the original design of the New England bulk power system to maintain system reliability and have been enhanced over the course of the 37-year existence of the grid.