This starting method requires that the motor has the possibility of connecting in two voltages, one being three times the other, and that the mains voltage is equal to the lowest of them, as an example: 220 / 380V; 380 / 660V; 440 / 760V. https://www.mrosupply.com/v-belts/v-belts/a-section/178197_a73_gates-rubber/ Suppose the motor is 220 / 380V. The application of this method will depend on the resistant conjugate imparted by the load and the current at the instant of the triangle connection, i.e., the resistant conjugate should not exceed the starting torque of the motor, and neither the current increase to a very high value at the instant of the bond triangle, facts that can make the method unfeasible.
The motor shall accelerate the load to approximately 85% of the rated speed at star connection at startup. In this situation, it starts with star connection, whose nominal voltage would be 380V. As the network supplies 220V, the motor starts with reduced voltage and for the network, this implies a starting current of 25% to 33% of the one that would present, if it were connected directly in triangle. The engine must accelerate the load to almost 85% of the rated speed. At this point we can switch to connection to triangle and for this to be permissible the nominal voltage at this connection must be equal to the mains voltage.