INTRODUCTION

The National Electric Reliability Council s Operating Committee (NERC-OC) is responsible for the promulgation of rules for its member companies so that power flow to consumers is reliable, especially on a regional basis. The control area is the basic unit recognized by NERC-OC. It may consist of a single large private company, a government-operated system such as the Tennessee Valley Authority, or several investor-owned companies banded together in a power pool.

The distinguishing feature of control areas is a single control center entrusted with the authority to operate the system within its area. The primary responsibility of a control area is to match its load with its own power generation. However, through interties with neighboring control areas, it is also prepared for mutual aid and scheduled sales of energy. Such mutual aid in emergencies may take the form of the flow of energy to a control area not directly adjacent to it. Even normally scheduled sales of energy may find intervening control areas between buyer and seller.

Frequency, measured in hertz (Hz), is the direct indication of the status of interconnected control areas. In North America, the normal frequency is 60 Hz. However, fluctuations in demand against generation cause all the interconnected control areas to witness the same variation in frequency (normally no more than 0.1 Hz). The frequency falls below 60 Hz when the demand exceeds the generation. Conversely, when the generation is...