(Updated; 5.6.2023.)
In addition to the Direct-On-Line (DOL) start, the oldest method of starting a three-phase squirrel cage motor is the Y-start, Δ-run starting, in which the starting current and torque are reduced to one-third of the nominal value.
However, recently, new similar starting methods have been applied to better adapt the motor starting to a specific load. In the following, three different methods will be explained using the example of the most common motor with 36 slots and 4 poles.
Therefore, in addition to the Y-start, Δ-run starting, which reduces the starting current to approximately 33% of its value, additional methods will be shown to reduce the starting current to 43%, 50%, and 60%.
Please note that reducing the starting current results in a proportional reduction in the starting torque.
FIRST METHOD 43%.
Below is the developed winding diagram (9 leads out) that achieves a reduction in the starting current to 43% of its value, along with an auxiliary diagram of this scheme for easier understanding.
Four coils are located in the Y-leg, while two coils are located in the Δ-leg.
SECOND METHOD 50%.
It is evident that with the above winding pattern, it is not possible to create a connection with an equal number of coils per Y and Δ-leg (it would disrupt the winding polarity). Therefore, for this case, we will use a different pattern called mixed winding (refer to the figures below).
THIRD METHOD 60%.
We will return to the first winding pattern but with a different internal connection. See the diagrams below.
Conclusion:
As it is evident, this enables us to better customize the motor to the specific load during production or repair: 33%, (43%, 50%, 60%), or 100%.
It should not be overlooked that any increase in the starting torque results in an increase in the starting current.
In fact, it is evident that these mentioned connections are very similar to the standard Y-start, D-run starting of the motor. By reducing the number of coils in the internal Delta, we move towards the classical 1Y connection (when there are zero coils in the internal triangle) and vice versa. The reduction of coils in the external Wye leads to the classical 1D connection.
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