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All voltage and line length values are approximations since strict accuracy is not necessary due to variables involved. Advantages of the lesser phase-angle shifts include: being applicable to lines of shorter length or lower voltage;2 nearer normal voltage at mid-point of the line from which ice is being melted;2 ice prevention on longer lines;2 reduction of relaying problems due to fewer lines being connected in series and reduced hazzard to customer service. Introducing the 120-deg roll has an added advantage in that the direction of a 60-deg phase shift can thereby be reversed, that is, from lag to lead. This provides flexibility to meet specific conditions of in-service ice melting such as location in the line of the larger conductors, service to primary networks, and capacity of facilities serving the remote end of various lines. Although applications of the 120-deg roll are described only as affecting phase-angle shifts in the lag direction, they are also applicable to lead angles when appropriate phase connections are made. Greater phase-angle shifts provide another range of nonstandard short-circuit voltages which make possible out-of-service ice melting on a still greater range of line lengths.
Power apparatus and systems, part iii. transactions of the american institute of electrical engineers (Volume:77 , Issue: 3 )
Date of Publication: April 1958