A) The rated voltage of a three phase induction motor is expressed on its name plate as 110V/220V. Can this motor be directly used in our country supply network? Justify your answer. Say and draw how the stator windings of this motor will be coupled in an environment of supply voltage 110V/220V. b) One-way switches are cheaper than push buttons; explain why push buttons are preferred to be used in motor circuits instead of one way switches. c) Draw the power diagram of a star delta starter two directions of control.

Motor rated at $110\,\text{V}~\Delta / 220\,\text{V}~Y$. Assume country three-phase supply is $220\,\text{V}$ line-line.

Rated $\Delta$ line voltage $= 110\,\text{V}$.
Supply voltage $= 220\,\text{V} > 110\,\text{V}$.

Phase voltage $= 220\,\text{V}$ (vs rated $110\,\text{V}$).
Overvoltage causes excessive flux, high magnetizing current, core saturation, overheating, insulation failure.

No, the motor cannot be directly used on $220\,\text{V}$ supply.

Rated $Y$ line voltage $= 220\,\text{V}$, matches supply.

Rated $\Delta$ phase voltage $= 110\,\text{V}$. Difference $\approx 15\%$, acceptable (no overload if current-rated).

Connect ends of three windings to form neutral point $N$.
Line $R$ to winding 1 start, $S$ to winding 2 start, $T$ to winding 3 start.
Winding 1 finish, 2 finish, 3 finish joined at $N$.

Justification: Matches rated $Y$ voltage, safe operation.

One-way switches: Simple on/off (SPST), cheap for lighting.

• Timed star-to-delta transition.
• Start/stop push buttons.
• Contactor interlocking (prevent simultaneous star+delta).
• Overload relays, fuses.
• Two-direction control needs reverse contactors.

Cannot sequence operations, no interlock, no remote control, unsafe arc on inductive load, no protection.
Adding auxiliaries increases cost/complexity beyond standard contactor setup.

No, low cost will not be achieved for motors.