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Dots in transformer symbols


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Hi Walid

i see often dots in transformer symbols, how these dots

This dots means the start of the winding. The windings is suposed to be wound at the same direction

How can I determine these dots practically on a real transformer.

Often you can't, you have to measure it! Else it is in the description of the tranny!

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You can but you'll need an oscillosope and a signal generator.

Connect the signal generator to the primary coil and to channel 1 of the oscillosope, connect the secondary to channel 2, no look at the phase differance, if they're in phase than the coils are wound in the same direction, if it's anti-phase then they're wound in opposite directions.

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The dots indicate the start of the winding, it doesn't matter if they are at the top or bottom, the only thing to note is if they're opposite to each other the signal in the secondary will be 180o out of phase to the primary.

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hi Alun
Assume that I have a transformer and I want to put its dots. I put it in a circuit, connect its primary with suitable AC volt then monitor the i/p & o/p on an oscilloscope if they are in phase I must put the dots on the primary and secondary points that connected to the +ve (center electrode) of the channel cables.
This is ok.
But here the dots may be at the ends of the coils rather than the start.
If the signals are out of phase, I must put dot at primary connected to the +ve and on secondary terminal connected to the -ve of the channel cable.
Is this what you try to tell me 100 years ago………
Thank you Alun.

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