First, the basic principles of motor protection selection
Currently, motor protection products on the market no uniform standards, model specifications varied. Manufacturers use in order to meet the needs of different users derive a lot of products, a wide range of users to the vast selection of inconvenience, the user selection should take full account of the actual demand for motor protection, rational choice and protection protection order achieve a good protective effect, to improve the reliability of equipment operation, reducing unplanned shutdowns, reducing accident loss purposes.
Second, the basic method of selection of motor protection
(A) with a selection of related conditions:
Selection of motor protection and motor protection exists both equipped with how reasonable relationship, here are a few conditions and protection-related factors, provide a reference for the user selection.
1, the motor aspects: first understand the model specifications, the motor features, protective type, rated voltage, rated current, rated power, power frequency, insulation class and so on. These basic content to give users how to properly use and maintain and selection protectors provide a reference.
2, environmental conditions: mainly refers to room temperature, heat, cold, corrosion degree, vibration degrees, sand, altitude, electromagnetic pollution.
3, the motor uses: mainly refers to machinery and equipment requirements drag characteristics, such as fans, pumps, compressors, machine tools, oil field pumping units and other mechanical properties of different loads.
4, the control system: control mode with manual, automatic, local control, remote control, stand-alone independent operation, the production line centralized control and so on. Starting directly, buck, star delta, frequency sensitive rheostat, inverter, soft start and so starts.
Five other areas: customer care on-site production management is more casual or serious, non-normal shutdown of the production of the severity of the impact.
There are a selection of the motor protector certain there are many related factors, such as with the installation location, such as the power situation, and distribution systems; also consider the purchase of new motor protection configuration, or upgrade to motor protection, or accident motor protection being perfect; motor protection should also consider ways to change the difficulty and extent of the impact on production; according to the actual operating conditions to be considered protector selection and adjustment.
(B) common types of motor protector
A thermal relay: general small-capacity AC motor, good working conditions, there is no frequent starts and other harsh conditions, due to poor accuracy, reliability can not be guaranteed, not recommended.
2, the electronic type: three-phase current detected value, setting the current value using the potentiometer knob or DIP switch operation, the circuit is commonly used analog, using inverse or definite time operating characteristics. Protection features include overload, phase loss, stall fault protection, fault type is displayed using LEDs, run electricity use digital display.
3, intelligent: three-phase current detected value, protection using SCM to achieve intelligent integrated motor protection, set protection, measurement, communication, display as a whole. Setting current digital set by the operator panel button, the user can according to their actual requirements and the protection of their own in the field correction setting various parameters, using digital tube as a display window, or using a large-screen LCD, can support for multiple communication protocols, such as ModBUS, ProfiBUS, the price is relatively higher for the more important occasions, the current high-voltage motor protection are used intelligent.
4, the thermal protection type: heating element embedded in the motor, according to the temperature of the motor protection, the protection effect is good, but the larger the motor capacity, the need to monitor the type used in conjunction with the current, to avoid a sharp rise in the temperature of the motor stall, due to temperature lag element, resulting in damage to the motor windings.
5, the magnetic field temperature detection type: buried in the motor magnetic field detection coil and temperature probe, rotating magnetic field changes and temperature changes be protected according to the motor inside, the main features include overload, stall, phase loss, overheating protection and wear monitoring, protection function, the disadvantage is the need to install the magnetic field detection coil and a temperature sensor in the motor.
(C) motor protection type working conditions in the motor selection
1, for the less demanding working conditions, the operation simple control, monitoring, management, more casual, down to the little influence of the single production run independently of the motor, you can use an ordinary type of protection, due to simple common type of protection structure, on-site installation wiring , replace, easy to operate, convenient, cost-effective and high.
2, for demanding working conditions, safety and continuity of very critical, and the high degree of automation, and the need for hand control, monitoring, management, MCC network monitoring system needs, and should be used in high-end functionality than the whole the protector.
3, for the explosion-proof motor, due to wear and tear caused by the eccentric bearing, the friction may cause explosion gap at high temperatures, resulting in an explosion hazard, should choose to wear condition monitoring functions. For large-capacity high-pressure submersible pump, due to inspection and maintenance difficulties, but also the wear condition monitoring function should be selected to avoid sweep chamber accident caused major economic losses.
4, used in explosion-proof requirements protector workplace, according to the specific requirements of the application site, choose the appropriate type of explosion protection, to avoid accidents.
