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Some misunderstandings in the use of frequency converter

2020-11-12

Improper choice


This should be the situation that friends encounter the most, big horse pulling car, small horse pulling cart everywhere. The big horse pulling the small car is good, at least there is no big problem in use. At most, the investment is increased, and the equipment can still run normally. However, the small horse can not pull the cart. When the load is small, it runs normally. Once the load is larger, the vegetables will stop, and the equipment will alarm frequently, which is very annoying.


Many friends like to choose the frequency converter by comparing the power of the motor, for example: 15kw motor with 15kw inverter, 30kW motor with 30kW inverter. But in fact, the selection of frequency converter, power is only a reference, more often need to refer to the motor running current and actual load


Over protection


When many users use the frequency converter, considering that the frequency converter is a high-value device, in order to protect it, a pile of protection devices will be added at the inlet side of the frequency converter, such as fuse, thermal protection relay, leakage circuit breaker, etc. But in fact, today's inverter itself has a very perfect protection function, such as: over-voltage protection, over-current protection, open phase protection, under voltage protection and so on.


In the installation guide of standard frequency converter, only contactors, circuit breakers and reactor are needed in the inlet side of frequency converter, and more protection devices may be counterproductive. When designing the installation of frequency converter, users should try to implement it according to the standard installation guide of frequency converter.


Power on frequently


During the debugging or operation of the equipment, it is often necessary to power off and restart the equipment. The operator will power on after the power is cut off, and then power on again immediately Such operation is absolutely life-saving behavior for frequency converter. Because most of the inverter hardware design has a start-up resistance, it will quickly heat up within a few seconds of power on, and then after the capacitor charging is completed, the starting resistance will cut out the main circuit through the bypass contactor, and then slowly cool down.


If the inverter is powered on and off frequently, the starting resistance may be overheated or even burned out. Therefore, the frequency converter user manual will explain the frequency converter power-off interval time, generally not less than 60s, different frequency converter time will be different. When using the frequency converter, please pay attention not to power on and off frequently!


Current leakage


We have encountered several times that the frequency converter trips as soon as it is powered on, resulting in power failure. After investigation, it is found that the user has installed a leakage circuit breaker at the inlet side of the frequency converter. In this case, we will suggest that the user either install an isolation transformer on the incoming side of the power supply, or remove the leakage circuit breaker, or simply disconnect / cut off the EMC grounding terminal inside the frequency converter.


Because most frequency converters have built-in EMC filter to prevent interference from entering, the filter must be grounded to work normally. However, the leakage current must be caused by the EMC grounding. Generally, the frequency converter will produce leakage current of tens to hundreds of Ma at the end of the EMC filter. When the threshold value of the common leakage circuit breaker is set at several hundred Ma, it is easy to be broken down and cause the protection action.


Energy saving


A few years ago, when energy conservation and emission reduction publicity was booming, the frequency converter was really on fire for a while. No matter what type of application, it seems that as long as the inverter is added, it can reduce energy consumption and emissions. But in fact, the use of frequency converter does not necessarily save energy. Whether it can save energy completely depends on its load type and operating conditions. Only in the appropriate application, the appropriate occasion, the inverter can play the effect of energy saving.


Such as centrifugal fans, pumps, such as the load, if the power frequency before 50 Hz Operation, and do not need to use baffles or valves to adjust the air volume and water pressure, the use of frequency converter will only increase energy consumption and waste resources; and if you need to adjust the air volume or water pressure with the help of mechanical devices, you can reduce the motor speed by using the frequency converter, which can reduce the energy consumption while saving the air volume and water pressure


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