Drive motor protection and market Electric lifting bracket

 

Protector

The function of the motor protector is to provide comprehensive protection for the motor. When the motor is overloaded, phase loss, locked rotation, short circuit, overvoltage, undervoltage, leakage, three-phase imbalance, overheating, bearing wear, device for alarm or protection when stator and rotor are eccentric. It can be used in telescopic mast.

Common sense of motor protection

1. The current motor is easier to burn down than in the past: due to the continuous development of insulation technology, the design of the motor requires not only increased output, but also reduced volume, the heat capacity of the new motor becomes smaller and smaller, and the overload capacity becomes weaker and weaker. Moreover, due to the improvement of production automation, the motor is required to run frequently in frequent starting, braking, forward and reverse rotation, variable load and other methods have put forward higher requirements for motor protection devices. In addition, the application of motor is wider, and it often works in extremely harsh environment, such as humidity, high temperature, dust, corrosion and other occasions. All of these have caused the current motor to be more easily damaged than in the past, especially the faults such as overload, short circuit, phase failure and sweeping bore have the highest frequency.

2. The protection effect of the traditional protection device is not ideal: the traditional motor protection device is mainly thermal relay, but the thermal relay has low sensitivity, large error, poor stability and unreliable protection. The same is true. Although many devices are installed thermal relay, the phenomenon of motor damage affecting normal production is still common.

3. Development status of motor protection: at present, the motor protector has developed from the past mechanical to electronic and intelligent, which can directly display the current, voltage, temperature and other parameters of the motor, with high sensitivity, high reliability, multiple functions, convenient debugging, and clear fault types after protection action not only reduce motor damage, but also greatly facilitate fault judgment, it is conducive to fault handling on the production site and shortening the recovery time. In addition, using the air gap magnetic field of the motor to detect the eccentricity of the motor makes it possible to monitor the wear state of the motor online. Through the curve showing the change trend of the eccentricity degree of the motor, bearing wear and inner circle can be found early, go to the outer circle and other faults, so as to find and deal with them early to avoid the accident of sweeping the bore.

3. Principle of protector selection: reasonable selection of motor protection devices can not only give full play to the overload capacity of the motor, but also avoid damage, thus improving the reliability of eletric power drive system and the continuity of production. The specific function selection should comprehensively consider factors such as the value of the motor itself, the type of load, the environment of use, the importance of the main equipment of the motor, whether the withdrawal of the motor has a serious impact on the production system, etc, strive to achieve economic rationality.

4. Ideal Motor protector: the ideal motor protector is neither the most functional nor the so-called most advanced, but should meet the actual needs on site and achieve the unity of economy and reliability, it has a high performance-price ratio. According to the actual situation on site, select the type and function of the Protector reasonably. At the same time, consider the installation, adjustment and convenience of the Protector, and more importantly, choose high-quality protector.

Selection of motor protector

Basic principles of selection:

At present, there is no unified standard for motor protection products on the market, and there are various models and specifications. Manufacturers have derived many series of products in order to meet the different needs of users, with a wide variety of products, which brings a lot of inconvenience to the selection of users; Users should fully consider the actual needs of motor protection when selecting, reasonable selection of protection function and protection mode can achieve good protection effect, improve equipment operation reliability, reduce unplanned parking and reduce accident losses.

 

Based on the selection method:

1. Conditions related to selection

1) motor parameters: first understand the rating of machine model, functional characteristics, protection type, rated voltage, rated current, rated power, power frequency, insulation grade, etc. These contents can basically provide reference basis for users to correctly choose protectors.

2) environmental conditions: mainly refers to normal temperature, high temperature, high cold, corrosion degree, vibration degree, Wind Sand, altitude, electromagnetic pollution, etc.

3) motor application: mainly refers to the requirements and characteristics of dragging mechanical equipment, such as fan, water pump, air compressor, lathe, oil-pumping machine and other mechanical characteristics of different loads.

4) control mode: The control mode includes manual, automatic, local control, remote control, independent operation of single machine, centralized control of production line, etc. Starting methods include direct, step-down, star angle, frequency sensitive rheostat, frequency converter, soft start, etc.

5) other aspects: the monitoring and management of on-site production by users, the severity of the impact of abnormal shutdown on production, etc.

There are still many factors related to the selection of protectors, such as installation location, power supply situation, distribution system situation, etc. It is also necessary to consider whether to configure protection for newly purchased motors or upgrade motor protection, the improvement of accident motor protection, etc.; The difficulty of changing the motor protection mode and the degree of influence on production should also be considered; The selection and adjustment of protectors should be comprehensively considered according to the actual working conditions on site.

2. Common types of motor protectors

1) thermal relay: ordinary small capacity AC motor, good working conditions, no frequent start and other harsh working conditions; Due to poor precision, reliability cannot be guaranteed, so it is not recommended to use.

2) electronic type: the three-phase current value is detected. The setting current value adopts potentiometer or dial switch. The circuit generally adopts analog type and adopts inverse time limit or fixed time limit working characteristics. The protection functions include overload, phase loss, blocking rotation, etc. The fault type is displayed by indicator light, and the running power is displayed by digital tube.

3) intelligent: detect the three-phase current value, and the protector uses single chip microcomputer to realize intelligent comprehensive protection of the motor, integrating protection, measurement, communication and display. The setting current adopts digital setting and is operated by the button of the operation panel. Users can modify and set various parameters on site according to the specific conditions of the motor. Digital tube is used as the display window or large screen liquid crystal display is used, it can support a variety of communication protocols, such as ModBUS, ProfiBUS, etc. The price is relatively high and it is used in more important occasions. Currently, high-voltage motor protection adopts intelligent protection devices.

4) thermal protection type: heat components are embedded in the motor, and the protection effect is good according to the temperature of the motor winding. However, when the motor capacity is large, it needs to be used in conjunction with the current monitoring type, avoid damage to thermometric element due to the lag of machine winding when the temperature rises sharply when the motor is locked.

5) magnetic field temperature detection type: the magnetic field detection coil and thermometric element are embedded in the motor to protect it according to the change of rotating magnetic field and temperature inside the motor. The main functions include overload, blocking, lack of phase, overheating protection and wear monitoring, the protection function is perfect, the disadvantage is that the magnetic field detection coil and temperature sensor should be installed inside the motor.

3. Selection of protector type

1) for single-machine independent running motors with low working conditions, simple operation and control, and little impact of shutdown on production, ordinary protectors can be used. Because of the simple structure of ordinary protectors, wiring is installed on site, it is easy to replace, easy to operate, and has the characteristics of high cost performance.

2) for the poor working conditions and high reliability requirements, especially the motors involved in automatic production lines, the medium and high-grade intelligent protectors with complete functions should be selected.

3) for explosion-proof electrical machinery, due to eccentric bearing wear, it may lead to high temperature of friction in explosion-proof clearance, resulting in explosion danger. The wear condition monitoring function should be selected. For large-capacity high-pressure submersible pump and other special equipment, due to the difficulty of inspection and maintenance, the wear condition monitoring function should also be selected, and the temperature of the bearing should be monitored at the same time to avoid major economic losses caused by the sweeping accident.

4) protection devices applied to places with explosion-proof requirements should be selected according to the specific requirements of the application site to avoid safety accidents.