For an induction motor, which of the following starters is the cheapest?

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.

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