Introduction to the measurement method of torque and speed characteristics of single-phase asynchronous motor

The torque speed characteristics of single-phase asynchronous motors refer to the relationship between the torque and speed of single-phase asynchronous motors from zero speed to synchronous speed, which is an important characteristic of asynchronous motors. The torque speed characteristic curve includes maximum torque, minimum torque, and locked rotor torque. The measurement methods include measurement output method, acceleration method, input method, and direct measurement method.
1、 Measurement output method for torque and speed characteristics of single-phase asynchronous motors
When measuring the torque speed characteristics of a single-phase asynchronous motor using the output method, the measurement data is used to take sufficient test points between 1/3 of the synchronous torque and the highest speed. Record the voltage, current, and torque at each speed point while maintaining a constant speed.
The calculation formula for the torque T corresponding to each speed n is:
In the formula:
T: Torque, in Nm
P0: Output power, unit: (W)
P1: Load wind friction, unit: (W)
n: Speed, in (r/min)
2、 Measurement of torque and speed characteristics of single-phase asynchronous motors using acceleration method
When using the acceleration method to measure a single-phase asynchronous motor, it is necessary to first calculate or measure the instantaneous inertia of the rotating components. When the motor accelerates from rest to near synchronous speed, the current and speed values are read from a fixed time interval. The torque T calculation formula is:
In the formula:
T: Torque, in Nm
Dn/dt: rate of change in rotational speed (r/min)
J: Instantaneous moment of inertia, unit: (kgm2)
k: As a constant, 109.7 * 10-4
3、 Measurement of torque and speed characteristics of single-phase asynchronous motors using input method
When measuring the torque and speed characteristics of single-phase asynchronous motors using the input method, it is required that the input power reading be plotted against the speed, and the line voltage, power, and speed should be plotted as a function of time, including the average value of 0 speed in the locked rotor type.
The torque T at each speed is calculated using the following formula based on the input power:
In the formula:
T: Torque, in Nm
k: Is a constant, 9.55
Pcu1: Copper loss of stator, unit: (W)
P1: Input power, unit: (W)
n: Speed, in (r/min)
Tfw: Wind friction torque of the motor at speed n, in Nm
4、 Direct measurement method for torque and speed characteristics of single-phase asynchronous motors
When directly measuring the torque and speed characteristics of single-phase asynchronous motors, continuous numerical measurement should be used. When the equipment cannot achieve continuous measurement data, a dynamometer can be used instead. When using a dynamometer for measurement, the speed at which torque is measured should be selected at intervals that ensure the maximum torque in the basic characteristics is drawn.
The minimum torque determines whether the motor can start smoothly, the maximum torque determines the overload capacity of the motor, and the rated torque represents the output power of the motor. So accurate measurement of torque and speed characteristics is very important for improving motor design and improving motor quality