Testing method for efficiency of synchronous motors
The measurement methods used for motor efficiency testing vary among different motors. Today, let's take a look at the methods and how to test the efficiency of synchronous motors.
Synchronous motor, like induction motor, is a commonly used AC motor. The efficiency measurement of synchronous motors is very important. Only by accurately measuring the efficiency of the motor and understanding its performance characteristic curve can effective methods be found to improve the efficiency of synchronous motors.
Synchronous motor is a commonly used induction AC motor, and its efficiency measurement includes direct measurement method, indirect measurement method, calorimetry method, and self deceleration test method. The more commonly used methods are direct measurement method and indirect measurement method.
Direct measurement method for efficiency measurement of synchronous motors
1 Braking method
When the tested motor operates as an electric motor, it is connected to a brake or dynamometer, and the torque of the tested motor is measured using the brake or dynamometer. At the same time, its speed is measured to determine the output power of the motor, and the input power is measured using a power analyzer or other electrical instruments.
When the test motor is running as a generator, use a dynamometer to drag the test machine and measure the input power of the test motor, using a power analyzer or other electrical instruments.
Due to the direct impact of motor speed on power calculation, the measurement of speed requires great accuracy.
2. Calibration motor method
The tested motor is mechanically coupled with a calibrated motor, and the input or output power of the tested motor is measured using a calibrated motor. The input or output power of the tested motor is measured using a power analyzer or other electrical instruments.
3 pairs of towing method
Mechanically couple two identical motors, one running as an electric motor and the other running as a generator. Measure the input power of the motor and the output power of the generator using a power analyzer or other electrical instruments. When the operating conditions of the two motors are basically the same, it can be assumed that the losses are evenly shared. Therefore, the output power of the motor is the difference between the input power and half of the total losses, while the input power of the generator is the sum of half of the total losses.
Indirect measurement method for efficiency measurement of synchronous motors
The indirect measurement method for measuring the efficiency of synchronous motors puts forward high requirements for experimental measurement equipment. The indirect measurement method is the loss analysis method, which requires the measurement or calculation of various losses of synchronous motors, including constant loss P0, load loss Pcue, excitation loss Pf, and stray loss Pd.
Calorimetric method for measuring the efficiency of synchronous motors
The direct measurement method and loss analysis method are common methods for measuring the efficiency of synchronous motors. When neither method is available, the heat method can be used to measure the efficiency of synchronous motors.
The constant loss can be determined through the no-load motor method and the no-load generator method, and the mechanical loss and iron loss can be separated from the no-load characteristic curve of the synchronous motor. The current measurement value under rated current operation can be used to calculate the armature winding loss, excitation loss, brush loss, etc.
Synchronous motor efficiency measurement self deceleration test
The self deceleration test is mainly applicable to motors with large rotational inertia and difficulties in measuring various losses using other methods. During the experiment, the tested motor is connected to a frequency adjustable power supply, which can also be driven by other power machines and excited by an independent DC power supply. Firstly, accelerate the tested motor to a speed slightly higher than the rated speed, and then cut off the power to allow the motor to self decelerate. Measure the time from high speed to set speed (95% rated speed for hidden pole machine and 90% rated speed for salient pole machine), and the time measurement accuracy between the upper and lower speed points should be within 2%. Measure the armature current and excitation current during the self deceleration process, and then calculate mechanical losses, constant losses, load losses, stray losses, etc. based on the measured data.
