Calculation of the Total Power Dissipation of Switch Gears: Principle

The total power dissipation of switch gears is calculated on the basis of the following calculation basis and methods:

Thermal design

The basis for the power dissipation calculation to determine a climate control solution is the definition of general conditions per project or per enclosure, taking into account the following factors:

Installation situation
Air-conditioning field
Voltage
Frequency.

To this purpose, specific calculation properties have to be defined in Rittal RiTherm. Further information is available here.

In addition, Rittal RiTherm zones (=air-conditioning fields in Eplan Pro Panel) must be defined by inserting physical and virtual partitions. Further information is available here.

Note:

The data for the calculation properties in Rittal RiTherm (apart from voltage and frequency) are not taken from the project properties and enclosure properties in Eplan Pro Panel, but are either calculated in Rittal RiTherm (power dissipation) or have to be entered there (for example the internal temperature or the ambient temperature).

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).

The factors for the definition of the general conditions are partially 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 GmbH & Co. KG 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 Properties tab are evaluated for the calculation of the busbar power dissipation:

Rail cross-section in mm²
Rail material (copper / aluminum / other material)
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: 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, 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. When calculating the total power dissipation in Eplan Pro Panel, the result of the calculation is automatically entered in the Thermal design: Total power dissipation for air-conditioning field [n] project property, where "n" designates the number of the air-conditioning field.