Selection of the basic principles
Currently, the market is no uniform standard motor protection, almost every manufacturer has its own model specifications. Manufacturers in order to meet the needs of different customers derive a lot of different uses of products, a wide selection to inconvenience the majority of users, the user selection should take full account of the actual demand for motor protection, rational choice protection and protection methods, in order to achieve good protection effect, to improve equipment operating reliability, reduce unplanned stop, reduce accident losses purposes.
Second, the motor protector
The basic method of selection
(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 relating to the protection 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 select and use the motor protector provides a reference.
2, environmental conditions: mainly refers to room temperature, heat, cold, corrosion degree, vibration degrees, sand, altitude, electromagnetic pollution.
3, the motor uses: such as fans, pumps, compressors, machine tools, oil field pumping units and other mechanical properties of different loads, such as water pump motor protection, it should have underload function, when the water pump smoked, protection needs given protection Directive.
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.
And motor protection
The selection of a 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, motor protection or to upgrade or improve motor protection against accidents etc; 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 selection and adjust the motor protector.
Common types (two) of the 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, lack phase protection function, reliability can not be guaranteed, not recommended.
2, motor protection: 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-time operating characteristics. Protection features include overload, phase loss, phase imbalance, such as fault protection, fault type using the indicator shows, such as UL-E2 series is such a motor protector.
3, integrated intelligent: three-phase current detected value, motor protection using SCM to achieve intelligent integrated motor protection, set protection, measurement, 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 prices are 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, the motor according to temperature protection, protection in general, and has a temperature lag, but the larger the motor capacity, the need to monitor the type used in conjunction with the current, to avoid stalling the motor when a sharp rise in temperature, due to the 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,Difficult in the complex field environments, currently only suitable for laboratory use.
(C) motor protector
Working conditions in the motor type selection
1, for the less demanding working conditions, the operation simple control, monitor, manage more casual, down to the little influence of the single production run independently of the motor, you can use an ordinary type of protection, because of the general type of protection structure is simple, 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 motor protector.
3, for the explosion-proof motors, 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, there is proof requirements apply to motor protector workplace, according to the specific requirements of the application site, choose the appropriate explosion-proof protection, to avoid accidents.
