dot convention of transformer

[ravit245]

Here in first image current is flowing from +ve to -ve in primary side but in equlent ckt current flowing from -ve to +ve.

plz explain





thanks
ravi

 

[BradtheRad]

The dots are there to indicate polarity of the windings.

It's in case the circuit couples the windings together in some way. They might need to be in sync or in opposition, depending on the circuit.

For example some oscillators use inductive coupling between windings to generate a feedback pulse.

Or in case there is another winding which needs to be hooked up in series. For example, in order to double the voltage.

If the purpose is simple step up or down, then it's not crucial whether the dots are at the same end or at opposite ends.

 

[pico]

The dot is used to indicate same polarity. It does not matter which polarity it is at that monent, but same polarity.

 

[atripathi]

to understand dot convention: at dot If current is entering in one winding, it would leave from end where dot is, at other winding. Assuming direction of winding is same.
So in second picture indicates that that direction of one of the winding is reverse in comparison to one shown on LHS.

Hope this clarifies.