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Advantages of Three Phase Motors Over Single Phase

Leah Spencer

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Most electric motors are used to convert electrical energy into mechanical energy, though some are utilized for production of force. Available in different shapes and sizes, they are found in various household items and industries. You can see the smallest electric motor in a wrist watch. Other applications include industrial and household fans, machine and power tools, water pumps, pipe line compressors, etc. Motors with highly standardized dimensions and features, achieve essential quantity of mechanical energy that is required for industrial purposes. Commonly seen motors in industries are the three phase motors. A three phase motor consists of a stator made of three phase windings secured inside a closed rotor.

Advantages of three phase motors

Advantages with respect to construction

• A three phase motor possesses three ‘hot’ legs carrying power supply, compared to single phase, where there is only one ‘hot’ leg and one neutral.
• Most importantly, three phase motors are smaller in size for the same horse power.
• Three phase motors have a simpler design unlike single phase motors.

Technical advantages

• Single phase motors above 10hp are less efficient. So they are manufactured in less numbers and are usually less common.
• Three phase motor has a high starting torque when compared to single phase motor.
• A three phase motor requires less copper, which leads to lesser weight
• Compared to single-phase motors, vibration is less in three phase motors. They have a longer life due to this reason
• Three phase motors are self-starting unlike single phase motors.
• Another advantage is that, if a three phase motor is loaded at less than 75% of rated torque, then efficiency lowers mildly down to 25%
• The sine waves of power supply are 120 degrees apart in a 3 phase motor, whereas it is 180 degrees apart in a single phase motor.
• They have a long life; say around 20,000 to 50,000 hours.
• A three phase motor requires only 3 - 4conductors unlike single phase that uses 6.
• Power loss is much less compared to single phase motors.
• Single phase motors require a capacitor to run or start the motor, whereas in three phase motor, it is not necessary.
• Also, as there are no brushes and capacitor in three phase motor, there are less moving parts and hence, less vibration.
• If a three phase motor is running in the reverse direction, just reversing any two leads will change direction of run. This process is difficult or sometimes not possible in single phase motors.

Cost comparisons

• Given the same voltage and rating, a three phase motor is highly efficient.
• As there is less copper and no capacitor, three phase motors are less expensive compared to single phase motors.

Other advantages

• Reversing a three phase motor into a single phase is very easy.
• They can withstand high temporary overloads.
• They produce less or no noise.
• There is no exhaust emission.

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