The peripheral equipment of the inverter mainly includes cables, contactors, air switches, reactors, filters, braking resistors, etc. Whether the selection of the peripheral equipment of the inverter is correct and suitable also directly affects the normal operation of the inverter and the service life of the inverter, so it is necessary for us to select the peripheral equipment correctly after selecting the inverter. Let's briefly explain the precautions for the selection of inverter peripheral equipment.
1. The setting and selection of the incoming circuit breaker
On the power supply side of the inverter, install a circuit breaker for wiring in order to maintain the wiring on the primary side. The choice of circuit breaker depends on the power factor on the supply side (varies with supply voltage, output frequency, load). Its operating characteristics change due to the influence of high-frequency current, so it is necessary to select a large capacitance.
2. Incoming contactor
Inverters can be used without incoming contactors. The incoming contactor can be aborted, but the braking function of the inverter will not be used at this time.
3. Motor-side contactor
If a contactor is installed between the inverter and the motor, it is forbidden to switch during operation in principle. When the inverter is connected during operation, there will be a large inrush current, so the inverter overcurrent maintenance action.
When a contactor is installed to switch to the power grid, it is necessary to switch the inverter after the output is stopped, and the speed search function must be used appropriately.
4. The setting of the thermal relay
In order to prevent the motor from overheating, the inverter has an electronic thermal maintenance function.
However, if one inverter drives multiple motors and multi-stage motors, set up a thermal relay between the inverter and the motor. The thermal relay is set to 1 times the motor nameplate at 50 Hz and 1.1 times at 60 Hz.
5. Improvement of power factor
To improve the power factor, a communication reactor can be inserted into the inverter inlet or a DC reactor can be added to the DC circuit.
When the output side of the inverter is connected to the capacitor filter to improve the power factor, there is a risk of damage and overheating due to the high-frequency current output of the inverter, and other inverters will overcurrent and current maintenance, please do not connect the capacitor filter.
6. About radio wave disturbance
There is a high-frequency component in the output (main circuit) of the inverter, which can cause disturbance to the communication equipment (such as AM radio) used in the vicinity of the inverter. In this case, a filter can be installed to reduce disturbance. In addition, the inverter and the motor and power supply wiring can also be grounded with metal pipes, which is also effective.
7. The wire diameter and wiring interval of the power cable
When the wiring interval between the inverter and the motor is long (especially when the low-frequency output is low), the torque of the motor will decrease due to the voltage drop of the cable; The application of abundant and thick cable wiring; When the operator is installed elsewhere, please use a special connecting cable; When operating remotely, the interval between the analog, control line and inverter should be controlled within 50 meters; The control signal is properly shielded and grounded.
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