ABSTRACT
A main reason for frequency and voltage control is the variation of the load. Fairly soon the end users started to put higher demands on the quality of supply, that is, on the voltage profile and the frequency, so automatic controllers and regulators had to be introduced to meet these requirements. The voltage control and the primary frequency control of generators are examples of local controls. As with the frequency control, the voltage control is also divided into primary, secondary, and tertiary voltage control. The North American Electric Reliability Corporation (NERC) is the entity nowadays in charge of setting reliability standards, which include basic frequency and voltage control requirements for the interconnected North American power grid. NERC establishes the minimum frequency and voltage control requirements to guarantee the reliable operation of the full interconnected North American grid; regional coordinators and entities in charge of the various control areas may set more stringent requirements.
