Discussion on Reasons and Protection of Air Compressor Motor Damage

Air compressor is abbreviated as air compressor. As a general-purpose mechanical equipment, it is widely used in the field of industrial and agricultural production. The problem is that the motor (three-phase asynchronous motor) as the power equipment of the air compressor generally has a higher failure rate than other motors. What is the reason? This article will put forward the basic concepts and arguments about the reasons for the damage of the air compressor motor and how to protect it. It is hoped that it will be able to attract the attention of the air compressor manufacturing industry and users and participate in the discussion.

   Air compressor motor damage analysis

   The reasons for the damage of the air compressor motor are various and comprehensive. We conducted in-depth investigations on air compressor work and production sites and found that the reason for the damage of the air compressor motor is related to the failure factors caused by the specific operation of the air compressor, in addition to the common failure factors of other motor power equipment. . The analysis summarizes the following points:

   Air compressor working conditions requirements

The mechanical operation of the air compressor, the electrical control is relatively simple (especially the low-power type), generally a single unit works independently, in a situation where there is no professional monitoring operation, and the occurrence of failures is not handled in time. Relatively speaking, the repeated expansion rate of failures increase.

  The reliability and sensitivity of the air pressure automatic switch

   The start and stop of the air compressor are usually directly driven by the air pressure automatic switch (air pressure relay) to directly drive the AC contactor to automatically control the motor. And the air pressure from

Most of the movable switches adopt a mechanical structure, and use springs to compress and release energy to operate the contacts. Perhaps it is due to the congenital deficiency of the automatic air pressure switch or the influence of different reasons such as improper adjustment and machine vibration. In the process of controlling air pressure, two abnormal actions may occur from time to time:

  1. The automatic air pressure switch refuses to operate when the air pressure is over, so that the motor can not operate normally, and the air pressure continues to rise, causing the motor to run overloaded and overloaded. In severe cases, failure and blockage may occur.

  2. The transient bounce phenomenon of the air pressure automatic switch (especially when the air pressure is close to the upper limit or lower limit critical state), and the AC contactor generates synchronous bounce. As a result, the main contacts of the AC contactor burn out or stick under frequent starting current impacts, causing shutdown or phase failure operation.

   Automatic exhaust valve malfunction

Air compressors generally do not have automatic exhaust devices. When the air pressure reaches the set pressure, it will automatically exhaust and reduce the pressure after stopping. The preset next time no-load start, after the exhaust valve fails, the air pressure in the air compressor cylinder cannot be released. When the motor starts under load, it may cause difficulty in starting or stall failure.

   Sudden power outage during operation

   The air compressor with automatic gear control encounters a sudden power failure (such as mains, self-provided power conversion), and restarts because the air pressure in the cylinder of the air compressor is too late to release. When the motor is under heavy load, it is likely to cause a stall fault.

   Start too frequently

  Because of the irregular peripheral air consumption, when the air consumption is large, the motor is forced to start frequently. The accumulation of heat surplus generated by the large current during starting is not easy to dissipate, which will cause the motor to overheat and possibly cause the motor to burn.

   Heavy load shutdown

  The shutdown of the air compressor, unlike other equipment, is to shut down when the maximum pressure is reached. The AC contactor acts in sections under heavy load and high current. At this time, the arcing spark is the most serious, posing a great threat to the damage of the AC contactor. Due to the damage of the AC contactor, it will cause the nature of the power failure. Such as unbalance (phase loss) and other operating conditions.

   The mechanical nature of the air compressor is faulty

   The air compressor is of uneven load nature, with high vibration and noise, and mechanical failures such as abrasion and damage caused by the obstruction of transmission parts, which can easily cause motor overload (locked rotor, blockage, etc.).

   Current Status of Air Compressor Motor Protection

   The above-mentioned typical failure factors show that the correct and reasonable protection of the air compressor motor is very urgent and necessary. However, so far, the protection device of the air compressor motor is still based on the thermal relay. Of course, as a traditional protection product, thermal relay has the advantages of simple structure, convenient use, low price, and certain inverse time characteristics, but its working principle and performance characteristics determine its small function, high power consumption, low precision, and setting. Rough, susceptible to environmental influences, poor repeatability, large errors and other shortcomings and defects. Reliable protection cannot be achieved for malfunctions such as locked rotor and long-term overload during the motor starting process, so it cannot meet the actual protection requirements of the air compressor. Therefore, protection failure is also an undeniable fact. Society is developing, science and technology are advancing, and backward products are being eliminated. Thermal relays have completed their historical mission.

  Protection starter (for air compressor)

   The new generation of electronic motor protector is the product of the advanced electronic technology era. It has the incomparable and unachievable functional characteristics of thermal relay. The protective starter (for air compressor), hereinafter referred to as the starter, is a derivative series of a new generation of electronic motor protection products developed for the special protection needs of air compressors. The protection of the air compressor motor has a more scientific, more reasonable and correct protection effect. It solves the problem of poor contact of the switching element due to the push of the air pressure automatic switch during the use of the air compressor, incorrect displacement of the free end of the elastic element, and frequent actions of the air pressure automatic switch, causing the AC contactor to jump instantly and continuously, and the heat cannot Dispersion, causing the main contacts of the AC contactor to burn out or the contacts to stick, leading to the lack of phase or over-current operation of the motor, thereby causing the motor to burn out; it fills the domestic magnetic starter with a special motor protector module to protect the starter blank.

  Features

  A. The starter is designed with operation, phase failure, and overload fault status indications to provide users with convenient maintenance.

  B. The starter performs signal detection and memory for the entire process of air compressor starting, running and stopping, and automatically adapts to the thermal power requirements of the air compressor motor, and can take different protection action times for different thermal conditions of the motor.

c. Since the starter is equipped with cold state and hot state overload protection characteristic K coefficient curve detection circuit and unbalance detection circuit, it can prevent phase loss, overload, and locked rotor that may occur during the starting and running of the air compressor motor. , Blocking, three-phase unbalance and other faults are protected by inverse time limit characteristics.

  D. The starter is designed with a self-check function, which can distinguish whether the power input terminal and itself work normally, and take corresponding self-locking measures.

e. The starter effectively solves the problem that the automatic air pressure switch refuses to act when the air pressure is overpressure, causing the motor to be overloaded or severely blocked, and the air pressure automatic switch transient vibration (suspected electric shock phenomenon, especially The air pressure is close to the upper limit or lower limit critical value state), and at the same time, the AC contactor produces continuity and synchronization, so that the main contact of the AC contactor under the impact of high current, the heat cannot be dissipated and burns out or sticks to cause the problem of lack of phase operation .

  F. The starter effectively solves the problem that the remaining air pressure in the cylinder cannot be released after the check valve fails, and the air compressor cannot be stopped or unloaded, causing the motor to overload and burn out. g. The starter effectively solves the problem that the air compressor is forced to start frequently due to the irregular air consumption of the air compressor. In addition, the large current is generated during the start, and the heat surplus is accumulated and not easily dissipated, which makes the motor temperature rise too high. The problem is difficult to protect.