Components surrounding a frequency converter mainly include cables, contactors, circuit breakers, reactors, filters, and braking resistors. The correctness and suitability of these components directly affect the normal operation and lifespan of the frequency converter. Therefore, after selecting a frequency converter, it is crucial to choose its peripheral components correctly. Below is a brief explanation of the considerations for selecting frequency converter peripheral equipment.
1. Installation and selection of incoming circuit breakers
On the power supply side of the frequency converter , please install a circuit breaker for the primary wiring to protect it. The selection of the circuit breaker depends on the power factor on the power supply side (which varies with power supply voltage, output frequency, and load). Its operating characteristics are affected by high-frequency current, so it is necessary to select a large-capacity circuit breaker.
2. Incoming contactor
The inverter does not have an incoming contactor available. An incoming contactor can be used for stopping, but the inverter's braking function will be unavailable in this case.
3. Motor-side contactor
If a contactor is installed between the frequency converter and the motor, switching between them during operation is generally prohibited. Connecting the contactor while the frequency converter is running will result in a large inrush current, triggering the frequency converter's overcurrent protection.
When installing a contactor for switching to the power grid, be sure to switch after the inverter has stopped outputting, and use the speed search function appropriately.
4. Setting of thermal relay
To prevent the motor from overheating, the frequency converter has an electronic thermal protection function.
However, when one frequency converter drives multiple motors or multi-stage motors, please install a thermal relay between the frequency converter and the motors. The thermal relay should be set to 1 times the value on the motor nameplate at 50Hz and 1.1 times the value at 60Hz.
5. Improvement of power factor
To improve the power factor, an AC reactor can be inserted into the inverter's input line or a DC reactor can be added to the DC circuit.
When a capacitor filter for improving the power factor is connected to the output side of the frequency converter, there is a risk of damage and overheating due to the high-frequency current output by the frequency converter. In addition, it will cause the frequency converter to overcurrent, triggering the current protection. Please do not connect a capacitor filter.
6. Regarding radio wave interference
The inverter's output (main circuit) contains high-frequency components, which can interfere with communication equipment (such as AM radios) used near the inverter. Installing a filter can reduce this interference. Alternatively, grounding the inverter, motor, and power supply wiring with a metal conduit is also effective.
7. Wire diameter and wiring distance of power cables
When the wiring distance between the frequency converter and the motor is long (especially at low frequency output), the motor torque will decrease due to the voltage drop of the cable; use sufficiently thick cables for wiring; when the operator is installed elsewhere, please use a dedicated connecting cable; when operating remotely, the distance between analog signals, control lines and the frequency converter should be controlled within 50 meters; the control signals should be properly shielded and grounded.
