Answer Posted / romil verma

When the motor is connected in Delta and started by DOL method, the voltage applied across a coil is the voltage between two phases i.e, 415V approx. Therefore the current inrush is high. In order to minimize the starting current, voltage across the coils should be brought low, which can be done if we connect the coils in star. During star connection the voltage across a coil is 240V (approx) which is 1/(sq root of 3)times that in delta which results in a simultaneous lowering of current also. This eases the stress on relays and conductors.When the motor attains 90% of its rated speed the coils are connected in Delta. therefore generating higher power.

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