Notes on the selection of peripheral equipment of frequency inverter

- Nov 29, 2019-

The peripheral devices of inverter mainly include cable, contactor, air opening, reactor, filter, brake resistance and so on.Whether the selection of the peripheral devices of the converter is correct and appropriate also directly affects the normal use of the converter and the service life of the converter.The following is a brief description of the attention to the selection of peripheral equipment of the converter. 

1. Setting and selection of incoming circuit breaker

To protect the primary wiring at the power side of the converter, please set a circuit breaker for wiring.The choice of circuit breaker depends on the power factor at the power side (which varies with the power supply voltage, output frequency, and load).Its action characteristic is affected by high frequency current and change, it is necessary to choose large capacity. 

2. Incoming contactor

No input contactor can be used for inverter.The inlet contactor can be stopped, but the inverter's braking function will not be used. 

3. Motor side contactor

If the contactor is set between the inverter and the motor, it is prohibited to switch during operation in principle.When the inverter is connected in operation, there will be a large shock current, so the inverter overcurrent protection action. 

When setting contactors for switching with the grid, be sure to switch after the converter stops output and use the speed search function appropriately. 

4. Setting of thermal relay

To prevent the motor from overheating, the frequency converter has electronic thermal protection function. 

However, when one inverter drives multiple motors and multistage motors, please set a thermal relay between the inverter and the motor.The thermal relay is set to be 1 times of the motor nameplate at 50Hz and 1.1 times at 60Hz.

5. Improvement of power factor

To improve the power factor, an ac reactor can be inserted into the input line of the converter or a dc reactor can be added to the dc circuit. 

When the output side of the inverter is connected with the capacitor filter to improve the power factor, there is a risk of damage and overheating due to the high-frequency current output by the inverter. In addition, the current of the inverter will be overcurrent, causing current protection. Please do not connect to the capacitor filter.

6. About radio interference

There is a high frequency component in the output (main loop) of the inverter, which can interfere with the communication devices (such as AM radio) used near the inverter.A filter can be installed to reduce interference.In addition, the inverter and the motor and power supply wiring can also be covered with metal grounding, is also effective. 

7. Line diameter and distribution distance of power cable

When the wiring distance between the inverter and the motor is long (especially the low-frequency output), the motor torque will decrease due to the cable pressure drop.Apply fully thick cable wiring;When the operator is installed elsewhere, use a special connection cable;During remote operation, the distance between analog quantity, control line and frequency converter should be controlled within 50 meters.The control signal is properly grounded.