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Which motor have relatively high starting torque?
Capacitor start
Capacitor run
Split phase
Shaded pole
Capacitor start
A Capacitor-start single-phase induction motor uses a high-value electrolytic capacitor in series with the auxiliary (starting) winding to produce a large phase difference (nearly 90┬░) between the auxiliary and main winding currents ┬╖ This large phase displacement creates a strong rotating magnetic field, resulting in a significantly high starting torque of about 300%┬аto┬а450% of full-load torque.
A Capacitor-start single-phase induction motor uses a high-value electrolytic capacitor in series with the auxiliary (starting) winding to produce a large phase difference (nearly 90┬░) between the auxiliary and main winding currents ┬╖ This large phase displacement creates a strong rotating magnetic field, resulting in a significantly high starting torque of about 300%┬аto┬а450% of full-load torque.
TsтАЛтИЭImтАЛIaтАЛsin╬▒ тАФ Starting torque equation where ╬▒ is the phase angle between main and auxiliary currents
╬▒тЙИ90┬░тЯ╣sin╬▒тЙИ1 тАФ Phase difference in Capacitor-start motor yielding maximum starting torque
During startup, both the main winding and the auxiliary winding (in series with a starting capacitor and a centrifugal switch) are energized from the AC supply ┬╖ The capacitor causes the current in the auxiliary winding to lead the supply voltage, creating a quadrature phase angle relative to the main winding current ┬╖ This quadrature current generates a high starting torque ┬╖ Once the motor reaches approximately 75% to 80% of its synchronous speed, the centrifugal switch opens to disconnect the auxiliary winding and capacitor.
Capacitor start induction motors develop a high starting torque (300%┬аto┬а450% of full-load torque).
The starting capacitor is typically a short-duty high-capacitance electrolytic capacitor.
A centrifugal switch disconnects the capacitor and auxiliary winding at 75%тИТ80% of synchronous speed.
High starting torque compared to split-phase and shaded-pole motors
Better power factor during the starting period
Higher cost due to addition of capacitor and centrifugal switch mechanism
Centrifugal switch contacts are prone to wear and mechanical failure over time
Compressors and Refrigerators
Pumps and Conveyors
Heavy-duty machine tools
| Feature | Capacitor Start | Split Phase |
|---|---|---|
Starting Torque (% FLT) | 300% - 450% | 150% - 200% |
Phase Angle (╬▒) | Nearly 90┬░ | 30┬░ - 40┬░ |
Starting Capacitor | Present (Electrolytic) | Absent |
Shaded pole motor has the lowest starting torque (around 40%тИТ50% of full-load torque).
Capacitor-run motor provides higher running efficiency and power factor, but lower starting torque (50%тИТ100%) compared to capacitor-start.
Option B (Capacitor run) uses a permanently connected continuous-duty paper/film capacitor resulting in low starting torque but quiet operation.
Option C (Split phase) produces moderate starting torque due to small phase angle difference (30┬░тИТ40┬░).
Option D (Shaded pole) produces very low starting torque and is used for small loads like fans.
A is correct тАФ Capacitor start motors provide a high starting torque (300%тИТ450% of full load) due to nearly 90┬░ phase displacement between main and starting winding currents.
Always remember the order of starting torque for single-phase induction motors: Capacitor Start Capacitor Run > Capacitor Start > Split Phase > Shaded Pole.