This special report was prepared by the Protection Aids to Voltage Stability Working Group of the Substation Protection Subcommittee. At the time the report was submitted for approval, May, 1993, the Working Group membership consisted of M. Begovic, D. Fulton, M.R. Gonzalez, J. Goossens, E.A. Guro, R.W. Haas, C.F. Henville, G. Manchur, G.L. Michel, R.C. Pastore, J. Postforoosh, G.L. Schmitt, J.B. Williams, K. Zimmerman. Contributions from former Working Group member A.A. Burzese are also acknowledged.