Efficiency testing method for synchronous motors

For the efficiency testing of motors, different motors use different measurement methods. Today let's take a look at the efficiency testing methods for synchronous motors and how to test them.

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 most commonly used methods are direct measurement method and indirect measurement method.

Direct measurement method for synchronous motor efficiency measurement

1. Braking method

When the test motor is operated as an electric motor, it is connected to the brake or dynamometer, and the torque of the test motor is measured using the brake or dynamometer. At the same time, its speed is measured to determine the output power of the motor. The input power is measured using a power analyzer or other electrical instruments.

When the test motor is operated as a generator, the test machine is dragged with a dynamometer and the input power of the test motor is measured with a dynamometer, and measured with a power analyzer or other electrical instruments.

Due to the direct impact of motor speed on power calculation, precise measurement of speed is required.

2. Calibration motor method

The test motor is mechanically coupled with a calibrated motor, and the input or output power of the test motor is measured using a calibrated motor. The input or output power of the test motor is measured using a power analyzer or other electrical instruments.

3. Dragging method

Mechanically couple two identical motors, one operating as an electric motor and the other 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 distributed. 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 synchronous motor efficiency measurement

The indirect measurement method for measuring the efficiency of synchronous motors places high demands on experimental measurement equipment. The indirect measurement method is the loss analysis method, which requires measuring or calculating the various losses of synchronous motors separately, including constant loss P0, load loss Pcue, excitation loss Pf, and stray loss Pd.

Measurement of synchronous motor efficiency using calorimetry

The direct measurement method and loss analysis method are the most common methods for measuring the efficiency of synchronous motors. When neither can be used, the thermal method can be used to measure the efficiency of synchronous motors.

Constant losses can be determined through the no-load motor method and no-load generator method, and the mechanical and iron losses can be separated from the no-load characteristic curve of the synchronous motor. The armature winding losses, excitation losses, brush electrical losses, etc. can be calculated based on the measured current values under rated current operation.

Efficiency measurement of synchronous motor and self deceleration test

The self deceleration test is mainly applicable to motors with large moment of inertia and other methods that are difficult to measure various losses. During the experiment, the tested motor is connected to a power source with adjustable frequency, or it can be driven by other power sources and excited by an independent DC power supply. First, accelerate the motor of the subject 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 the highest speed to the set speed (95% rated speed for hidden pole machines and 90% rated speed for convex pole machines), and the accuracy of time measurement 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.