Considerations in the Regulation of Interconnected Areas

A number of factors related to control of generation and power flow on interconnected systems are analyzed. Criteria by which effectiveness of regulation within an individual control area can be judged are examined. System control error is defined and its relationship to system frequency deviation and to system stored energy developed. In particular, inadvertent interchange is explored and its relationships to system time error for an area that regulates to zero control error is developed. Conditions under which the algebraic summation of inadvertent interchange around the interconnection would be zero are defined, and operating conditions when this would not be true are identified. This leads to an evaluation of the technique, used by some control areas, of correcting for inadvertent interchange by a unilateral change of net interchange schedule. The adverse effect which such unilateral action can have on the inadvertent accounts of other areas is pointed out. Quantitative relationships are derived which show the relatively small influence which unilateral schedule changes have on system frequency and time error. Also examined and noted to be of limited validity is the practice of deducting the time integral of the bias term from total inadvertent interchange to obtain unintentional inadvertent.