Calculation of the total power dissipation is effected on the basis of the following calculation basis and methods:
Thermal design
The basis for the power dissipation calculation is the definition of general conditions per project or per enclosure, with the following factors being considered in Rittal Therm:
- Installation situation
- Air-conditioning field
- Voltage
- Frequency.
The following factors are furthermore required for the "Thermal design" in EPLAN:
- Air-conditioning field
- Total power dissipation
- Simultaneity factor
- Maximum permitted power dissipation of the components
- Rated current (rails).
All the factors for the definition of the general conditions are properties of the parts or of the part placements whose values the user has to specify correctly in the project planning.
Calculation of the power dissipation of devices and busbars
Specific part properties are evaluated for the calculation of the power dissipation of the individual devices and busbars. The part properties are managed in the EPLAN parts management. These are specifications by the component manufacturer and data that are created and maintained by the user. EPLAN Software & Service does not accept any liability for the correctness of these specifications.
Devices
The power dissipation of a device is calculated in accordance with the formula:
Actual power dissipation of the device = Power loss x Simultaneity factor
- The power dissipation of a device is read from the Max. power dissipation part property.
- The simultaneity factor (default value = 0) is set via the Thermal design: Simultaneity factor project property as a factor for the project. It is an estimated value that takes into consideration the fact all the devices are never switched on simultaneously at full power in a plant. A deviating simultaneity factor can be set at each device. The simultaneity factor is stored at the functions in the Thermal design: Simultaneity factor (automatic) property.
The result of the calculation is stored in the Thermal design: Device power dissipation property.
Busbars
The following part properties located on the Busbar tab are evaluated for the calculation of the busbar power dissipation:
- Rail cross-section in mm²
- Rail material (copper / aluminum / other material)
- Specific electrical conductivity at +20 °C
- Temperature coefficient.
Notes:
- The temperature coefficient applies for a temperature of 20 °C.
- The busbar power dissipation is calculated for a mean rail temperature of 65 °C.
The following factors are required for the calculation of the busbar power dissipation in Watt [W]:
- Busbar operating current in Ampere [A] (from the Thermal design: Busbar operating current part property)
- Busbar resistance in Ohm [Ω] for one meter of busbar at +65 °C busbar temperature. Is calculated automatically from the part properties Rail cross-section, Specific electrical conductivity at +20 °C and Temperature coefficient, as well as the temperature difference Δθ [K] = 45K.
Calculation formula:
Formula symbols:
A = Rail cross-section in [mm²]
σ = Specific electrical conductivity in [MS/m] (= MegaSiemens per meter) or [m/(Ω x mm²)]
α = Temperature coefficient in [1/K] - Rail length in meter [m] (from the part reference property Subset / length in unit of project).
The busbar power dissipation is calculated with the following formula and entered in the Thermal design: Device power dissipation property:
Formula symbols:
I² = Busbar operating current in [A]
R(+65°C) = Busbar resistance in [Ω]
l = Rail length in [m]
Total power dissipation
The power dissipations of the installed devices and those of the busbar system are used for each air-conditioning field when the total power dissipation is calculated. The result of the calculation of the total power dissipation is entered in the Thermal design: Total power dissipation for air-conditioning field [n] project property, with "n" being the number of the air-conditioning field.
See also
Calculation of the Total Power Dissipation of Switch Gears