© THETA Ingenieurbüro GmbH 2015
Thermal Network Library
Theory
The Thermal Network Library is a highly efficient and self-explanatory unit that enables its users to dimension the most diverse
electrical components thermally on the basis of the RCL network programme OrCad PSpice (version 8 or higher). In order to
calculate temperatures, three processes have to be distinguished.
The heat generation processes are described mathematically in discrete sources:
•
ohmic loss dependent on the geometry of the conductor, the qualities of the conductor material, the load current, which is
available in different and defined characteristics, and the skin effect resulting from the system frequency
•
power of solar and sky radiation dependent on place and time
The heat transfer processes occuring in electrical devices and installations. They are described mathematically by discrete
resistances:
•
heat conduction dependent on the geometry of the conductor and the thermal conductivity of the conductor material
•
heat radiation dependent on the geometry and the surface qualities of the conductor
•
convection dependent on the geometry of the conductor, the gaseous or fluid cooling medium and the coolant velocity
•
convection in gas-shaped hollow spaces dependent on the geometry and the gaseous or fluid cooling medium
•
coolant circulation and coolant flow rate dependent on the gaseous or fluid cooling medium and the ventilation slots
This mathematical description is possible not only pressure-dependent for the media air, SF6 and nitrogene, but also for water and
insulating oil.
In order to examine electrotechnical devices and installations under dynamic aspects, heat storage processes in the form of heat
storage capacities have to be taken into consideration in the thermal network. These depend on the geometry of the conductor and
on its material values.
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