Condensation in the inverter cabinet? Don't be afraid. There are two ways to do it

China has a vast territory and a large number of frequency converters work in humid environment. For example, frequency converters installed in rainy southern coastal areas, frequency converters of wind turbines near humid mountains, frequency converter devices working in rivers and lakes, etc.

Affected by air humidity, once the ambient temperature changes greatly, the frequency converter may have condensation, and a certain amount of liquid water will be generated in its internal power devices, circuit boards and other parts. After mixing with the dust accumulated inside, the electrical insulation of the frequency converter will be seriously affected, and even a path will be generated, affecting the normal operation.

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For example, liquid water attached to the heat dissipation plate of power devices will lead to the formation of a path between the grid and drain of IGBT, seriously damage the grid of IGBT, and lead to the loss of normal function of IGBT. For another example, liquid water attached to the circuit board will lead to short circuit at the corresponding terminals, resulting in pulse confusion, and serious faults such as inter bridge short circuit.

Condensation will seriously affect and threaten the normal and stable operation of the frequency converter. If the frequency converter works in a humid environment, especially in the rainy south in summer, correct measures must be taken to prevent and eliminate condensation.

1、 Formation of condensation and its harm to frequency converter

The air under natural conditions is composed of a small amount of dust, water vapor and absolutely dry air. The water vapor that the 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 maximum temperature at which condensation occurs in air with specific humidity.

The water vapor contained in the air at higher temperature will be separated out in the form of liquid water due to the decrease of temperature. If the air with high humidity and relatively high temperature touches the solid surface of the frequency converter with relatively low temperature (lower than the dew point temperature of the air under this condition), condensation will occur, and then a certain amount of liquid water will be generated on the surface of relevant parts of the frequency converter.

When the liquid water is mixed with the dust inside the frequency converter, the corresponding conductive channel will be generated, which will affect the electrical insulation of the frequency converter, so that the non-conductive area will be transformed into a normal conductive area.

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For example, once mixed dust condensation is attached to the surface of IGBT power devices, a path will be formed between the gate and drain of IGBT, which will seriously damage the gate of IGBT and cause IGBT to lose its normal function; For another example, mixed dust condensation attached to the control circuit board will cause the circuit board to produce non-existent conductive channels, resulting in confusion of logic pulses, resulting in power short circuit, failure of electronic components and other faults.

Although some circuit boards are coated accordingly, condensation always occurs at the bottom of some components and circuit connections due to the influence of blind spots and other factors.

2、 Elimination of condensation

By destroying the condensation formation conditions such as temperature difference and humidity, the purpose of condensation can be fundamentally eliminated. If any formation condition is destroyed, the frequency converter will not condense.

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

temperature control

Preventing the formation of condensation can be achieved by destroying the condensation formation condition of temperature difference. Since the inverter cabinet is relatively closed, if the cabinet temperature can always be higher than the dew point temperature, condensation will not occur.

Influenced by this idea, there are mainly two temperature control schemes at this stage:

The first scheme includes vents and heaters. Generally, the vents are equipped with filters, which can not only prevent a large amount of dust from entering the inverter, but also ensure the IP protection level.

The main point of the scheme is to start heating once the humidity is too high, and increase ventilation when the temperature rises. When the humidity exceeds the preset value, promote the heating action, increase the internal temperature of the frequency converter, and then effectively control the relative humidity conditions. After the temperature reaches the preset threshold, start the ventilation, so as to make a certain amount of external fresh air enter the frequency converter, so as to ensure that the consistent air relative humidity inside and outside the frequency converter is always maintained, The temperature is always kept within the normal range. Generally, when the temperature exceeds 40 ℃, start the ventilation system, and when the relative humidity exceeds 80%, start the heater.

The main idea of the second scheme is: the internal cooling capacity of the frequency converter 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 frequency converter will be reduced, and the temperature in the frequency converter cabinet will be improved through the power consumption generated by the frequency converter, so as to eliminate condensation; When the temperature exceeds the threshold value, the heat dissipation capacity will be improved to prevent excessive temperature from affecting the normal operation of the frequency converter.

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