System Information Overview
The transmission system delivers electrical energy from generating stations to transmission customers and the distribution system. Originally, generating stations were located close to the load they served and the transmission system could be as simple as one line. Today a sophisticated networked system connects generating stations to substations which distribute electricity to customers. The transmission system in the strictest sense consists of
- wood poles and steel structures designed to safely support the wire conductors which run for many miles between substations; and
- substations which contain protection, metering, and communications equipment, transformation to other voltages, and/or voltage control equipment.
This transmission system is designed and operated to transfer large quantities of electricity reliably, safely, and efficiently. But there is more. The items above are only the transmission facilities. The entire "system" (and it is a system in the literal sense, for they all work together) is composed of much more:
- individual generators within a station, their associated excitation systems with fast voltage control, their associated turbines and governors to regulate frequency, their associated protective equipment, and the auxiliary loads to keep the generators operating;
- the distribution system, with its voltage regulators, power factor compensation, and protection systems;
- customer equipment, along with its protection and controls; and
- control centers and dispatchers, who issue orders to generators to match generation to load, and control flows, voltages, and frequency.
In fact, all of these facilities, not just the transmission facilities, make up "the system" in the larger sense. Moreover, "the system" extends across our entire continent, operating in synchronism. That is why reliability criteria for transmission system designers and operators apply to generation facilities and consider the behavior of distribution systems and customer equipment. That is also why the models for large-scale studies of system behavior model all of the above facilities across the continent. The eastern interconnected systems make up the largest machine in the world.
The MEPCO transmission system
The Maine Electric Power Company (MEPCO) transmission system carries bulk electricity at 345 kV between the Maine Yankee station in Wiscasset, Maine, and Keswick substation near Fredericton, New Brunswick. MEPCO owns and operates 182 miles of the 345 kV line from Maine Yankee station to the New Brunswick border, and New Brunswick Power owns and operates the other 49 miles of the 345 kV line from the Maine border to Keswick substation.
MEPCO provides the only interconnection between the Maritimes Control Area to the north in Atlantic Canada and Maine and the rest of the NEPOOL Control Area to the south in New England. 345 kV transmission lines are our ties to the eastern interconnected North American power grid. Between Keswick and Maine Yankee, MEPCO also interconnects 345 kV substations, specifically, from north to south, Chester, Orrington, and Maxcy’s. There is also high capacity voltage control equipment connected to the MEPCO transmission system, to support large power transfers over long distances:
- 80 MVAR of reactors (inductors) at Orrington,
- 200 MVAR of capacitors at Orrington, switched in three banks, and
- 450 MVAR capacitive, 125 MVAR inductive Static VAR Compensator (SVC) at Chester
|MEPCO Normal Interconnection Capabilities|
||Transfer Limit (MW)|
|New Brunswick to Maine
|Maine to New Brunswick
||150 to -350|
NEPOOL Normal Interconnection Capabilities
||Transfer Limit (MW)|
|Northern New England to Southern New England
||1,700 to 3,000|
|Quebec to Sandy Pond
||1,200 to 1,500|
|New York to New England
||1,300 to 2,000|
|New England to New York
||700 to 1,500|
This table illustrates that MEPCO and nearby power transfer limits are large when compared to local load. These power transfer limits can vary significantly with conditions are not necessarily the same in both directions.
MEPCO is a small part of a much larger bulk power system. Therefore, the coordination of system design and operation extends well beyond local system boundaries.
The New England Power Pool (NEPOOL) is a voluntary organization formed in 1971 to assure reliability, and to attain maximum practicable economy with equitable sharing of benefits and costs. Therefore NEPOOL has a dual role: reliability and economy. Over 99% of the electrical energy supplied in New England is provided by participants in NEPOOL. NEPOOL is organized along three lines; New England Power Planning (NEPLAN), New England Power Exchange (NEPEX), and sharing of benefits (NEPOOL Billing). New England operates as a single "Control Area". A series of standing Committees and Task Forces provides representation and peer review for NEPOOL Participants. Participation in NEPOOL was originally limited to customer-serving electric utilities, but has recently included Non-Utility Generators (NUGs) and Power Marketers and Brokers. NEPOOL relies on its "Reliability Standards", Criteria, Rules, and Standards (CRSs), Operating Guides (OGs), and Operating Procedures (OPs) to reliably design and operate the New England interconnected systems.
NEPOOL will host an OASIS site for all of the Transmission providers in New England. NEPOOL participants are currently negotiating to create a Regional Transmission Group (RTG) and an Independent System Operator (ISO) for New England.
The Northeast Power Coordinating Council (NPCC) is a voluntary organization formed after the 1965 Northeast Blackout to promote the reliability and efficiency of the electric bulk power systems by coordination of system design and operation. NPCC has a singular role; reliability. The NPCC region includes New England, New York, New Brunswick, Nova Scotia, Quebec, Ontario, Prince Edward Island, and Newfoundland. The Reliability Coordinating Committee and a series of standing Task Forces provides representation and peer review for NPCC members. Working Groups also perform special reliability assignments. Membership in NPCC was originally limited to customer-serving electric utilities within the region, but has recently included other utilities, Non-Utility Generators (NUGs) and Power Marketers. NPCC relies on its "Reference Manual", composed of Criteria, Guides, and Procedures to reliably design and operate the NPCC interconnected systems.
Disturbances in Maine can affect the bulk power systems west and south of New York, to the Gulf Coast and the Rocky Mountains. Similarly, disturbances elsewhere on our continent can affect Maine and northeast North America. Therefore, the regional reliability councils, such as NPCC, have coordinated their efforts in the North American Electric Reliability Council (NERC).
Transmission system reliability incorporates dependability and security. Dependability relates to the continuity of electricity to customers. In the event of equipment failure, system security ensures that system failures are localized, and significant long-term damage is minimized.
In order to ensure an adequate level of reliability in New England and northeast North America, criteria have been established to guide the design, operation and maintenance of power systems. NEPOOL and NPCC members agree to abide by criteria and guidelines that have been established by experience over the years, and inform all other members of any non-compliance. This forms the basis for reliable operation of the bulk power system in Maine and the northeast.
The transmission system allows access to outside energy markets for both economy and longer-term contractual transactions. It also accommodates the flows necessary to allow the economic dispatch of generation and tie flows under the NEPOOL Agreement.