ABSTRACT
Transmission systems must meet performance standards and criteria that ensure an acceptable level of quality of electric service. Voltage quality at the consumer connection is typically addressed at the distribution level and not by reinforcing the transmission system. Reliability criteria for transmission systems must address both local interruptions of power supply at points in the network as well as widespread interruptions affecting population centers or entire regions. Reflecting the different concerns of local interruptions and widespread interruptions, reliability objectives are different for the bulk transmission system than for the local area transmission or subtransmission systems supplying electric power to electric distribution systems. The concept of cost to consumers of unreliability expressed in dollars per year has emerged as a practical measure of reliability when comparing transmission reinforcement alternatives. In one approach, which is used to assess the reliability of supply to load centers, the impact of rare transmission failures are obtained from precomputed lookup tables of transmission import limits.
