Tie Line (electrical Grid)
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A balancing authority (BA) is an entity in the US electric system (as well as in parts of Canada and Mexico) that is responsible for grid balancing: resource planning and
unit commitment Power system operations is a term used in electricity generation to describe the process of decision-making on the timescale from one day (day-ahead operation) to minutes prior to the power delivery. The term power system control describes actions ...
ahead of time, maintenance of the load-interchange-generation balance within a balancing authority area (also known as a control area) and support for real-time
load-frequency control The utility frequency, (power) line frequency (American English) or mains frequency (British English) is the nominal frequency of the oscillations of alternating current (AC) in a wide area synchronous grid transmitted from a power station to th ...
.Glossary of Terms Used in Reliability Standards
North American Electric Reliability Corporation, p. 2. February 8, 2005.
The balancing authorities are connected by metered high-voltage tie lines and grouped into interconnections:U.S. electric system is made up of interconnections and balancing authorities
Energy Information Administration The U.S. Energy Information Administration (EIA) is a principal agency of the U.S. Federal Statistical System responsible for collecting, analyzing, and disseminating energy information to promote sound policymaking, efficient markets, and publ ...
(EIA.gov), July 20.2016.
* Eastern Interconnection consists of 31 balancing authorities in the US and 5 in Canada; * Western Interconnection consists of 34 balancing authorities in the US, 2 in Canada, and 1 in Mexico; * Electric Reliability Council of Texas includes a single balancing authority; * Quebec Interconnection also with a single authority.


Implementation

A typical balancing authority is an electric utility with an added responsibility to maintain a fine balance between the production and consumption of electricity, including ensuring availability of sufficient on-line generation resources and managing the electricity transfers from (and to) other balancing authorities. Balancing authorities operation is guided by mandatory reliability standards created by the North American Electric Reliability Corporation and approved by the US (
Federal Energy Regulatory Commission The Federal Energy Regulatory Commission (FERC) is the United States federal agency that regulates the transmission and wholesale sale of electricity and natural gas in interstate commerce and regulates the transportation of oil by pipeline in ...
) and Canadian regulators. The enforcement authority is delegated to regional entities (8 in the US). To coordinate activities across multiple BAs, a
reliability coordinator Reliability, reliable, or unreliable may refer to: Science, technology, and mathematics Computing * Data reliability (disambiguation), a property of some disk arrays in computer storage * High availability * Reliability (computer networking), ...
entity (RC) is used that has the power to reduce or cancel the interchange transactions and adjust the dispatch plans. Frequently the same utility plays multiple roles, for example, CAISO, in addition to being an independent system operator, is also operating under the name RC West as a reliability coordinator for 42 balancing authorities and transmission operators in the Western interconnection. The interactions between the BAs and RCs can be compared to the ones between pilots and air traffic controllers. A meter on a tie-line is shared between the two BAs interconnected by this line.


Operation

A balancing authority has the following responsibilities: * maintaining the balance between load, generation, and external transfers; ** short-term (load-frequency regulation); ** longer-term ( load following); * controlling the frequency and time error; * implementing the interchange transactions. The coordination tasks are performed by the balancing authority staff and the
automatic generation control In an electric power system, automatic generation control (AGC) is a system for adjusting the power output of multiple generators at different power plants, in response to changes in the load. Since a power grid requires that generation and load ...
(AGC) systems. The quantitative estimate of the balancing is provided through area control error (ACE, measured in MW), that as an indicator is conceptually similar to the role the frequency deviation plays at the interconnection level: positive ACE is pushing interconnection frequency higher. The operation of a BA is guided by two primary external inputs (that together form the ACE): * ''interchange error'', a difference between the planned and measured electricity flows through the tie lines; * frequency bias is a coefficient representing an obligation of the BA to provide or absorb energy in order to maintain the system-wide frequency or to assist in time control, it is a negative number expressed in MW/0.1 Hz. As a simple example, if frequency is lower than the 60 Hz target, the BA is typically expected to provide a (usually small) amount of additional power. More precisely, BA might be required to provide more energy if its import exceeds its bias obligation (defined as a product of the frequency bias coefficient and a difference between the actual and target frequency). To maintain the balance, a BA will dispatch the generators and, in some cases, will control the load with the goal to keep the ACE within predefined limits that are usually set to be proportional to the total load services by the BA. The control is maintained by multiple means: direct control of the generators by the computer systems, dispatch orders to power plants communicated by phone, load shedding in emergencies, and exchanging the electricity with other BAs.


References


Sources

* * * * {{cite book , last1=NERC , title=Balancing and Frequency Control , date=May 11, 2021 , publisher= North American Electric Reliability Corporation , url=https://www.nerc.com/comm/OC/ReferenceDocumentsDL/Reference_Document_NERC_Balancing_and_Frequency_Control.pdf Electric grid interconnections in North America