| 摘要 |
A proximity effect heat-tracing system in which proximity effect heat-tracing circuits are fed in either direction from a plurality of feed points connected to a single main transformer to increase the length of pipeline supplied by a single main transformer. A secondary transformer interposed between a main transformer and a plurality of feed points reduces the voltage required to be applied to a proximity effect heat-tracing system of a given length. Two or more proximity effect heat-tracing systems used along the same length of pipeline, employ neutral conductors having approximately the same diameter as "hot" conductors where the secondary of the main transformer in each system is 180 DEG electrically out of phase with the secondary of the main transformer in the other system. A center-tap secondary in each subsidiary transformer is connected to a heat tube so that each proximity effect heat-tracing circuit is connected between an end of a secondary winding of a subsidiary transformer and a center tap of a secondary winding of a subsidiary transformer in order to minimize current in the transformers secondaries. Selection of the turns ratios of subsidiary transformer remote from the main transformer compensates for the voltage drop along a transmission line connecting the main transformer with subsidiary transformers.
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