The absence of phase operation is one of the most critical issues that can lead to motor failure. However, the damage caused by motor stalling should not be overlooked. In an assembly line, if a motor becomes blocked for an extended period, it can result in the motor burning out and even causing damage to the entire system, leading to costly and irreversible consequences. Therefore, implementing stall protection for motors is essential, and this process typically begins with conducting a motor stall test.
Motor stalling occurs when the motor is unable to rotate but still produces torque. This condition is often triggered by foreign objects, mechanical failures, or human error. When the motor encounters excessive load, a foreign object gets stuck, or there's a malfunction in the drive mechanism or bearing, the motor may stop rotating entirely or fail to start.
When a motor operates normally, the magnetic field generated by the stator induces rotation in the rotor. As the rotor turns, it cuts through magnetic lines of induction, generating an induced current. This current creates its own magnetic field, which interacts with the stator field and helps reduce the current in the stator windings.
However, when a motor is stalled, this reverse-induced current cannot be generated. As a result, the voltage applied to the winding increases significantly, causing a sharp rise in current. At this point, the motor’s power factor drops dramatically, and the stall current can surge up to 5 to 12 times the rated current, depending on the motor’s size and construction. If the motor remains in this state for even a short time, it can quickly overheat and burn out.
To prevent such severe damage, motors are generally equipped with overcurrent protection devices. These systems are designed to trip the motor’s power switch when it detects prolonged blockage, preventing overheating and further damage. The correct current settings must be determined through testing, which is a crucial step in both new motor development and factory testing. Stall tests are especially important for ensuring motor quality and reliability.
The MPT1000 motor test platform offers a comprehensive solution for stall current testing. There are two main types of stall tests: conventional and those following national standards. The conventional test is a widely accepted method due to its simplicity, low cost, and ease of use. It involves applying the rated voltage to the motor under no-load conditions, then gradually increasing the load until the motor stalls. Alternatively, the MPT system can be used to directly block the motor and measure the resulting data.
During the stall test, a high-speed and high-precision data acquisition system captures key parameters such as torque, voltage, and current. These values are then analyzed using a power analyzer and an industrial computer, allowing for real-time display and storage of the data. This makes it easier to analyze and interpret the results, while also protecting the motor from damage during the test.
The national standard stall test follows the procedures outlined in GB/T 1032-2012, specifically in Chapter 9 on determining locked current and locked rotor torque. This test is primarily applicable to three-phase motors and may require additional voltage regulation equipment. However, with a programmable AC power supply, the entire process can be automated, making it more efficient and accurate.
Whether it’s a conventional test or a national standard one, these procedures provide reliable and accurate data that support motor design, performance evaluation, and fault diagnosis. With this information, engineers can better implement stall protection measures and improve overall motor reliability. Therefore, motor stall testing is an essential part of motor production and development.
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