Is A Three-kilowatt Single-phase Motor And A Three-kilowatt Three-phase Motor Equal in Horsepower?

Is a three-kilowatt single-phase motor and a three-kilowatt three-phase motor equal in horsepower?

A: The output horsepower between the 3KW single-phase motor and the 3KW three-phase motor is equal.

Because horsepower is a unit of power, but an older concept of an industrial revolution, the concept of horsepower is named by James Watt, an improver of the steam engine, to express the power of his steam engine relative to the pull of horses, at that time Watt defined imperial horsepower, converted to 1 imperial horsepower = 745.7 watts, and the unit of horsepower is "HP": so there is a metric horsepower unit, which is defined as: 1 horsepower = 735 watts, That is, 1 horsepower is equivalent to completing 75 kilograms in 1 second, and the weight is increased to 1 meter.

The three-phase motor has three sets of running windings, and there is a symmetrical phase angle of 120° alternating current between the three, and it can rotate itself according to the phase sequence of the power supply after the power supply is turned on, and no other auxiliary starting components are required.

Therefore, the current of the winding of the single-phase motor when working is greater than the current of the winding of the three-phase motor, so the size of the single-phase motor must be much larger, and the cross-sectional area of the winding enameled wire of the single-phase motor is larger than that of the three-phase motor.

where P2 is the rated output power, n is the motor efficiency, n is the motor speed, M is the motor torque, and 9550 is a constant. The torque calculation formula for single-phase motors is the same.

Now the question arises, why the same output power, but why are three-phase motors commonly used in industry, instead of one-way motors?

In fact, this is because the way of China's power supply system is three-phase four-wire system or three-phase five-wire system (their line voltage is 3x380V), and a wire is drawn from the O point of the L1, L2, L3 live wire in the three-phase winding coil as the neutral line N of the three-phase four-wire power supply, so that three lines with a voltage of 220V can be output.

So when we choose a motor, if the load requires a lot of torque, then choose a motor with a large number of poles. Because the more motor poles, the lower the speed and the greater the torque.

It's like a car that downshifts when going uphill. Because in the case that the engine output cannot be increased, reducing the speed can be exchanged for more torque, and thus more traction.

Due to the power supply, the starting torque of the three-phase motor is much larger than that of the single-phase motor; Because the single-phase motor itself has no starting torque, it can only run through a special structure to assist the start (such as capacitor start). Compared with single-phase motors, three-phase motors have the advantages of small size, large starting torque, high power factor, high efficiency, uniform torque and small current. Therefore, daily industrial use is a three-phase motor.