Which of the following starters is the most cost effective for an induction motor?

Correct option is D

Star-Delta Starter:
· This is the cheapest option among the listed starters.
· It uses a simple mechanism to initially connect the motor windings in a star configuration to reduce the voltage and current during startup.
· After the motor reaches a certain speed, it switches to a delta configuration for normal operation. This simplicity and lack of additional components keep the costs low.

​$$\textbf{Delta starting:}\\I_{st ( phase )} = \frac{V_1}{Z_{01}} \\I_{st ( phase )} = I_{st ( line )} = \frac{\sqrt{3}V_1}{Z_{01}}\\\textbf{Star connected starting}\\I_{st ( line )} = I_{st ( phase )} \\I_{st ( phase )} = \frac{V_1}{\sqrt{3}Z_{01}}\\\textbf{The ratio of currents of star connection and delta connection:}\\\frac{I_{st ( star )}}{I_{st ( delta )}} = \frac{\frac{V_1}{\sqrt{3}Z_{01}}}{\frac{\sqrt{3}V_1}{Z_{01}}} = \frac{1}{3}\\\text{The starting current with star starting is just } \frac{1}{3} \text{ rd when compared to direct delta starting.}$$​​