taneously. Electromagnetic wavespropagate inoilwithavelocity of about c/1.5. Therefore, 700psrepresents aspatial resolution of-14cm. A monitoring system usingthedischarge mapshould record a phase stamp foreachPDpulse captured. Oncedistinct clusters began toappear onthemap,theunderlying data could begrouped andplotted separately inphase-resolved form(oneplot perPDsource). Thisapproach wouldavoid theneedtoanalyze phase-resolved discharge patternscontaining superimposed signals frommultiple sources, potentially associated withdifferent phases ofthehighvoltage. Furthermore, someclusters onthemapmaybeextemal interference signals(conducted inthrough thebushings, perhaps). Onceidentified as such, these clusters could besuppressed sothat itwouldremain possibletodetect theonset ofsmall discharges inother regions ofthemap. A particularly interesting aspect ofthedischarge map(requiring further investigation) istheinterpretation oftheshape oftheclusters: A well-defined discharge source suchasarcing atafloating electrode maygiveasharp peakbecause theposition andorientation ofthecurrent pulse isconsistent [1]. Incontrast, surface tracking onpressboard mightappear asabroad humpbecause thedischarge position andorientation isquite variable. TheuseofonlytwoUHFsensors inthis study permitted agraphical presentation oftheinterpretation process. Usingathird sensor would addextra dimensions tothedischarge map, since comparisons could be madebetween three combinations ofsensor pairs instead ofone.Together withappropriate analysis software, theavailability ofthis extra datashould enhance theability ofthetechnique todiscriminate betweenPDsources andremove muchoftheambiguity conceming the location ofeachdischarge. Conclusions: A technique foranalyzing UHFsignals frompartial discharge sources that allows themtobeseparated according totheir point oforigin hasbeendescribed. Thedischarge mapcanenable simultaneous monitoring ofmultiple discharge sources inthepresence of interference. Incontrast toacoustic PDmeasurements ontransformers, thepropagation delay experienced byUHFsignals isaninsignificant fraction ofthe50/60 Hzcycle. Consequently, phase-resolved PDmeasurements canbemadewithout theneedforadditional electrical timing signals. Theconcept ofdischarge mapping introduced hereforpower transformers could equally beapplied toother encapsulated insulation systems. Investigations arecurrently underway tointerpret therelationship between theshape ofclusters onthedischarge mapandthephysical characteristics ofthedischarge source. Procedures forautomatically locating thedischarges inthree dimensions using acoarse modeloftheintemal transformer structure arealso being developed.