The dew point is the temperature for which a device reaches 100% of humidity and generates the condensation phenomenon.
The dew point only depends on the parameters at the time of installation:
Mounting phase:
From Mollier's diagram:
Absolute humidity = Function (ambient air temperature) for various relative humidity ratios
=> absolute humidity = 0.009 Kg of water//kg of dry air
Operating phase:
Move from ambient air (near bars or enclosure) to 55°C
=> the volume of air around the conductors increases (constant pressure and increasing temperature)
=> the quantity of water remains constant in a larger volume of air
=> the relative humidity ratio decreases: 10% as per Mollier's diagram Installation
Shutdown phase:
Still as per Mollier's diagram, for a constant absolute humidity =0.009 Kg of water/kg of dry air
To estimate the dew point of a busbar trunking, we must:
The dew point only depends on the parameters at the time of installation:
- Ambient air temperature
- Humidity % (RH) in ambient ai
- Example: Mounting equipment at 20°C ambient temperature and 60% humidity, then move to 55°C ambient temperature before stopping the installation
Mounting phase:
From Mollier's diagram:
Absolute humidity = Function (ambient air temperature) for various relative humidity ratios
=> absolute humidity = 0.009 Kg of water//kg of dry air
Operating phase:
Move from ambient air (near bars or enclosure) to 55°C
=> the volume of air around the conductors increases (constant pressure and increasing temperature)
=> the quantity of water remains constant in a larger volume of air
=> the relative humidity ratio decreases: 10% as per Mollier's diagram Installation
Shutdown phase:
Still as per Mollier's diagram, for a constant absolute humidity =0.009 Kg of water/kg of dry air
- - if ambient air moves to 20°C => the relative humidity ratio moves back to 60%
- - if ambient air moves to 12°C => the relative humidity ratio moves to 100 %
To estimate the dew point of a busbar trunking, we must:
- Know or estimate the ambient temperature and the relative humidity ratio during equipment mounting:
- Typical values are:
- ambient temperature = 20°C
- relative humidity ratio = 60%
- estimation of absolute humidity by reading on Mollier's diagram
- for estimated absolute humidity, read on Mollier's diagram the temperature for which a relative humidity ratio = 100% is reached