Hazards and precautions of inverter condensation

Frequency converters have a wide range of applications, and condensation can seriously affect the normal operation of frequency converters. The author first discusses the generation of condensation and its hazards to the inverter, and introduces the main methods to eliminate condensation, and on this basis, combined with examples, analyzes the causes of inverter accidents, and proposes corresponding preventive measures.

A large number of inverters are widely used in all walks of life in China. Due to the wide range of applications and the vast territory of our country, there are bound to be a large number of inverters working in humid environments, such as inverters installed in China's humid and rainy coastal areas and southern regions, or inverters installed in rivers and lakes and humid mountains near wind turbines, or inverter devices working in rivers, lakes and seashores.

Affected by air humidity, once the temperature of the working environment changes greatly, it may lead to condensation phenomenon of the inverter, so that its internal power devices, circuit boards and other parts produce a certain amount of liquid water, which will have a serious impact on the electrical insulation of the inverter after mixing with the dust accumulated inside the inverter, and will also produce a path, resulting in the failure of the inverter and affecting the normal operation.

For example, the adhesion of liquid water to the heat sink of a power device will cause a path to form between the gate and drain of the IGBT, and seriously damage the gate of the IGBT, causing the IGBT to lose its normal function. For example, liquid water adheres to the circuit board, which will cause a short circuit in the corresponding terminal, which will cause pulse confusion, and in serious cases, it will also lead to the occurrence of fault phenomena such as short circuit between bridges.

Through the above introduction, it can be found that the condensation phenomenon will seriously affect and threaten the normal and stable operation of the inverter, once the inverter works in a humid environment, it is necessary to take the right measures to prevent and eliminate the condensation phenomenon.

1 The formation of condensation and its hazard to the frequency converter

The air under natural conditions is composed of a small amount of dust, water vapor and absolutely dry air. The amount of water vapor that air can hold is directly proportional to the ambient temperature, that is, the higher the ambient temperature, the more water vapor the air can hold. The so-called dew point temperature refers to the higher temperature at which condensation occurs in the air at a particular humidity.

Water vapor contained in the air at higher temperatures will be precipitated in the form of liquid water due to the drop in temperature, which can no longer be contained in the air. If the air with high humidity and relatively high temperature hits the solid surface of the inverter with a relatively low temperature (lower than the dew point temperature of the air under these conditions), condensation will occur, and a certain amount of liquid water will be generated on the surface of the inverter-related parts.

When the liquid water is mixed with the dust inside the inverter, the corresponding conductive channel will be generated, which will affect the electrical insulation of the inverter, so that the area that should not be conductive will be converted into a normal conductive area.

For example, once the mixed dust condensation adheres to the surface of the IGBT power device, it will cause a path to form between the gate and drain of the IGBT, which will seriously damage the gate of the IGBT and cause the IGBT to lose its normal function. Another example is mixed with dust condensation attached to the control circuit board, which will make the circuit board produce conductive channels that do not exist originally, resulting in confusion of logic pulses, and then produce power short-circuits, electronic component failures and other faults.

2 Methods of eliminating condensation

By destroying the conditions for condensation such as temperature difference and humidity, the condensation phenomenon can be fundamentally eliminated. If any of the formation conditions are destroyed, the inverter will not condensate.

At present, the more common and commonly used condensation elimination methods are: temperature control method, the former aims to reduce the relative temperature, and the humidity control method, the latter aims to reduce the relative humidity.

1) Temperature control

Preventing the formation of condensation can be achieved by destroying the condensation formation condition of the temperature difference. Since the inside of the inverter cabinet is relatively closed, if the temperature of the cabinet can always be higher than the dew point temperature, no condensation will occur. Influenced by this idea, there are two main temperature control schemes at this stage:

One option includes vents and heaters, etc. In general, the vents are equipped with filters, which not only prevent large amounts of dust from entering the inverter, but also ensure the IP protection level.

The main point of the solution is to start heating as soon as the humidity is too high, and to increase ventilation when the temperature rises. When the humidity exceeds the preset value, the heating action is promoted, the internal temperature of the inverter is increased, and the relative humidity conditions are effectively controlled, and the ventilation is started after the temperature reaches the preset threshold, so that a certain amount of external fresh air enters the inverter, so as to ensure that the internal and external humidity of the inverter is always consistent and the temperature is always kept within the normal range. In general, the ventilation system is activated when the temperature exceeds 40°C, and the heater is activated when the relative humidity exceeds 80%.

The main idea of the second scheme is: the internal cooling capacity of the inverter is relatively controllable, to ensure that the temperature in the cabinet is always maintained within a certain range, when the humidity exceeds the threshold, the heat dissipation capacity of the inverter is reduced, and the temperature in the inverter cabinet is increased through the power consumption generated by the inverter, so as to prevent the occurrence of condensation; When the temperature exceeds the threshold, the heat dissipation capacity is improved, and the normal operation of the inverter is prevented from being affected by excessive temperature.

Most of the inverter cabinets under this scheme are completely sealed, which effectively prevents salt spray, harmful gases and dust from entering the cabinet, which is convenient for the long-term, reliable and normal operation of the inverter.

2) Humidity control

By reducing the water vapor content, the relative humidity of the air is effectively reduced, so as to eliminate the occurrence of condensation. It mainly includes the following three schemes: temperature difference dehumidification method, adsorption and membrane dehumidification method and condensation dehumidification method.

Temperature difference dehumidification method: install a radiator conducive to condensation inside the inverter, so that the condensation is only formed on the radiator, so that condensation will not form in other parts of the inverter, and the condensate formed on the radiator is discharged outward through the outlet, so as to ensure that the cabinet always maintains a relatively dry environment.

Adsorption and membrane dehumidification method: the corresponding adsorption material is set in the inverter cabinet to achieve the purpose of water vapor adsorption to ensure that the cabinet always maintains a relatively dry environment; It can also be set up through the membrane filter to block water vapor, only let the dry air pass through the filter, so that only relatively dry air flows into the inverter.

Condensation dehumidification method: set a low temperature point inside the inverter, so that the condensation only occurs there, so as to effectively reduce the relative humidity inside the inverter, so that the inverter always maintains a relatively dry environment.

Hazards and precautions of inverter condensation

Hazards and precautions of inverter condensation

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