Thermal Network 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. 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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