1. Electrical parameter matching
Current range and transformer: The current range of the protective device must match the rated current of the motor. For example, the rated current of a 22kW/380V motor is about 42A, and a protector with a 50A range should be selected. If a current transformer (CT) is used, ensure that the secondary output of the transformer matches the input of the protector (eg 150:5A).
Working voltage: The voltage level of the control power supply needs to be confirmed. Common ones are 220V AC or 24V DC.
2. Load conditions and operating characteristics
Starting type and time characteristic curve: An appropriate tripping curve needs to be selected according to the starting characteristics of the motor to ensure that the protector can avoid the starting current. Class 10 is recommended for light load start (<3 seconds, such as fans); Class 20 is recommended for standard start (3-10 seconds, such as conveyors); Class 30 is recommended for heavy load start (>10 seconds, such as crushers).
Impact load: For reducers with impact loads, a long delay needs to be set to avoid the start-up time (such as 20 seconds for a centrifugal fan to start). At the same time, the locked-rotor protection current is usually set to 5-7 times the rated current, and the action time should be 10%-20% longer than the starting time to prevent false triggering.
3. Mechanical characteristics and auxiliary protection
Coupling selection: To cope with impact loads, a suitable coupling must be matched. Elastic pin couplings are suitable for medium impact (such as fans, water pumps); diaphragm couplings are suitable for high-precision, high-speed scenarios; snake-shaped spring couplings have good elasticity and can withstand large torque impacts, and are often used in heavy machinery such as mining and steel rolling.
Torque monitoring: For high-precision or high-risk equipment, torque sensors and controllers can be configured to quickly cut off power in milliseconds when impact overload is detected.
Structural reinforcement: Large reducers can be equipped with a rigid base to improve installation stability, and use shock-absorbing pads (such as rubber pads, spring pads) to isolate vibration transmission and reduce the risk of resonance.
4. Protection device types and functional requirements
Power and cost decision: When the motor power is less than 7.5kW, you can choose a lower-cost thermal relay (<200 yuan); when it is greater than 7.5kW, it is recommended to choose an electronic or intelligent motor relay.
Communication and monitoring needs: If you need remote monitoring, you should choose a protector that supports industrial bus protocols such as Modbus, PROFINET or Ethernet (high-end solutions are usually more than 800 yuan); if you only need local display, you can choose an economical solution with LED display and relay output (300-500 yuan).
Redundant protection: For key equipment (such as fire pumps and compressors), "temperature sensor + current" dual-signal redundant protection must be configured to improve system reliability.
5. Operating environment requirements
Protection level: The device installed in the power distribution cabinet can choose IP20 protection level; if it needs to be installed on-site in a harsh on-site environment, it needs to choose IP65 or above protection level.
Special environment: In an explosion-proof environment, an increased safety motor must be selected with a flameproof (Ex d) protector.
6. Parameter setting and debugging
Overload coefficient setting: The overload protection setting current is usually set to 1.05~1.2 times the rated current of the motor, and the higher value is used under heavy load conditions.
Phase loss protection sensitivity: Follow the principle of "the lighter the load, the higher the sensitivity". Use the standard sensitivity when running at full load, and adjust it to the highest sensitivity when running at light load (<40%) to prevent the motor from burning due to phase loss at light load.
