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Topic Title: U,V,W, R,S,T vs L1,L2,L3
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Created On: 30 September 2011 10:40 AM
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 30 September 2011 10:40 AM
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I've just been looking at a generator set and the busbars in the terminal box are labeled U,V,W, in accordance with IEC 60034-8 "Terminal markings and direction of rotation" (had to look that up because at first I thought that was incorrect and should have been L1, L2, L3 :-/). However the corresponding switchgear is marked R,S,T instead of L1, L2, L3. I've not seen that before and wondered if anyone knew the standard that it came from?

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 30 September 2011 10:51 AM
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In a three-phase generator there are three windings, typically designated as A-B-C, R-S-T or U-V-W.

Phase rotation (or phase sequence) describes the order (A-B-C, R-S-T, or U-V-W) of the phase voltages at the output terminals of a three-phase generator. The generator phase rotation must match the facility phase rotation.

So if the facility phase rotation is R-S-T then U to R, V to S and W to T.


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 30 September 2011 05:07 PM
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These designations come from the old Continental standard which goes right back to the early days of three-phase equipment.

R-S-T was the general designation for the three phases of the supply system.

U-V-W and X-Y-Z were then used to designate the connections to the windings on motors, generators, etc. The individual windings were U to X, V to Y, and W to Z. So for a wye generator configuration, for example, X, Y, and Z would be strapped together to form the neutral point, and the phases R, S, and T would be fed from the U, V, and W winding terminals respectively.

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