Substation Voltage Upgrading

Conversion of lines and substations to higher voltage has emerged in the industry as a viable alternative in meeting load growth or transmission requirements. This somewhat unconventional approach offers several advantages. Beyond the practical aspects such as use of available right-of-way and substation site, the economic advantages may be of considerable interest, particularly if some of the original foundations, structure, or equipment can be used with minimal modifications. In recognition of utility industry\´s needs, Electric Power Research Institute (EPRI) has initiated a research project on "substation voltage upgrading" (RP2794-1). The objective of this project is to explore the possibilities of and to develop methods for substation voltage conversion. This paper summarizes the early findings of this project, including the results of a utility survey and the review of present industry practices and standards. Survey of 48 North American utilities has shown that there exist considerable voltage conversion activities for substations rated up to 242 kV. However, the practice of substation voltage "uprating" (i.e., using some of the original equipment or existing layout/BIL) is very rare, as opposed to complete substation rebuilding, or voltage "upgrading." The present practices in substation insulation design are based on standards, some of which date back to older technologies in overvoltage protection and smaller economic incentives to utilize available margins at lower operating voltages. Figure 1 illustrates the relationships between per unitized recommended BILs versus rated maximum voltage. Since both scales are logarithmic, a constant BIL appears as a straight line.