The creeping danger
FACILITIES MANAGEMENT CONDENSATION
STEGO
The creeping danger
Humidity - condensation - corrosion :
This chain of adverse conditions often adds up to cause failure in sensitive electrical and electronic components . The use of modern electric enclosure heaters is an effective and economic countermeasure that addresses these frequently neglected causes of defect and avoids damage or even breakdowns .
Operational reliability and longevity are attributes every customer expects from an enclosure . The controllers increasingly feature sensitive electronics . For some electronic components , the service life is directly related to the ambient temperature . This requires the interior temperature of switching cabinets to be lowered and unwanted excess heat to be removed . This is achieved through ventilation via filter fans .
The danger arising from condensation in electric cabinets is often disregarded , however , even if the resulting defect characteristics are usually very dramatic . Short circuits cause damages in individual units that must then be replaced . This cause of defect occurs - under certain climate conditions - even in well encapsulated enclosures .
Condensation - a rarely recognized cause of faults or even complete breakdowns of an entire control system
In combination with aggressive gases and dust particles , condensation causes atmospheric corrosion . Affected are , e . g .:
• bus bars • contactors
• relays • protective motor switches
• transformers • frequency inverters
• programmable controls
• semiconductors / circuit boards
• solder , crimp and screw connections
Condensation is thus a source of faults that must be taken seriously . The biggest risk in practice occurs when relatively high humidity and temperature fluctuations coincide in an encapsulated enclosure - e . g ., during round-the-clock operation or in outdoor installations . Failure causes triggered by condensation in systems can be :
• changing contact resistances • indefinable stray currents • reduced insulation properties
• arcing up to total short circuit • corrosion occurring
There ’ s something in the air
Humidity arises when the sun extracts water from waterways and plants by evaporation . This share of water vapor in the atmospheric air is referred to as “ absolute ” humidity ( in g / m ³). How much water can be stored in the air depends on a variety of factors , such as temperature or air pressure . The higher the air temperature , the more invisible water parts can be absorbed by and stored in the air . The ratio of “ absolute ” humidity to the max . possible humidity is referred as “ relative ” humidity ( in %). At 100 % RH , the air is saturated , and the so-called dew point is reached . No further water vapor can be stored in the air . The excess water vapor share is dumped into the environment as condensation .
Dew - refreshing for nature , devastating for technology
At constant absolute humidity ( water quantity in g / m ³) and falling temperature , the air becomes saturated and can no longer hold the water vapor : the dew point is reached , and fine water droplets are deposited . This process can easily be observed on windows , spectacles and drinking glasses when the condensation occurs on the cold surfaces . This is when the danger of component failure in enclosures begins .
Outdoor installations are particularly at risk : condensation already forms as a result of temperature changes between mild daytime temperatures and overnight cool down , but even more so as a result of seasonal climate change or sudden temperature drops - such as during thunderstorms in summer .
Even in indoor installations , temperature changes trigger condensation . The culprits are bus bars , relays and other heatgenerating installations mentioned at the beginning that work in a day-night cycle .
If these are switched off at night , they no longer heat the air inside the electric cabinet . This cools down and the relative humidity rises . The consequence is the formation of condensation .
Corrosion even without condensation
The formation of condensation only starts when a relative humidity of 100 % is reached . But even values lower than that can present a danger for switching cabinets . Corrosion can already occur at much lower values . This is the result of various long-term studies . The empirical limit thus determined is at around 65 % RH . From this threshold on , one has to expect corrosion in electric cabinets , even without condensation being formed .
Optimal conditions can only be achieved for constant temperature . Condensation and corrosion are not the only factors that significantly reduce the lifetime of the components - so does the mechanical stress brought about by continuous temperature change .
The “ life insurance ” for switching cabinets : electric enclosure heaters
The state-of-the-art solutions are electric enclosure heaters that have been developed specifically to avoid condensation and temperatures that are too low or fluctuate too much . The air in the electric cabinet is heated to the point where it can hold the entire water vapor and condensation is avoided . Just this is what would happen when equipment is switched off and no excess power is dissipated . Without heater , the relative humidity increases and condensation occurs on the components .
Conclusion :
Electric cabinet heaters are a reliable protection against condensation and temperatures that fluctuate or are too low . When comparing the cost caused by failures to the purchase price of electric cabinet heaters and controllers , the latter represent little additional cost that nevertheless makes a big difference .
For further information , please visit www . stego . co . uk
68 PECM Issue 62