3 winding transformer doc

docs/user_manual/components.md

@@ -330,6 +330,12 @@ It can happen that `tap_min > tap_max`. In this case the winding voltage is decr
 increased.
 ```
 
+#### Electric Model
+
+`three_winding_transformer` is modelled as 3 transformers of `pi` model each connected together in star configuration. 
+However, there are only 2 `pi` "legs": One at `side_1` and one in the centre of star. 
+The values between windings (eg. `uk_12` or `pk_23`) are converted from delta to corresponding star configuration values. 
+The calculation of series and shunt admittance from `uk`, `pk`, `i0` and `p0` is same as mentioned in {hoverxreftooltip}`user_manual/components:transformer`.
 
 ## Appliance