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When I look at electrical transformers mounted on utility poles, only one wire goes from the high voltage phase line into the transformer. However, in every electrical circuit, current goes from one terminal, through a load a comes back to the generator by the other terminal. So where is the returning current wire on a utility transformer for the primary high voltage winding? Does the high voltage current enters the transformer and doesn't come out? How's that possible?
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- William (age 25)
You are right, William, it takes two wires to tango in a transformer. But there is a trick. In what is called the SWER or Single-Wire Earth Return system the 'other wire' is the earth itself. Usually the external case of the transformer is connected to one end of the primary coil and the 'hot' end is connected to the power line. The case is then connected to the earth by means of a wire that attaches to a rod that is pounded into the ground. The current than travels through the ground back to a distribution point or back to the generator. There is a safety danger in this system since if the ground wire is somehow broken and you touch the case then you will be attached to the high voltage power line. Not good.
(published on 09/03/2009)
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