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 (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 the product of the frequency bias coefficient and the 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 ==