Silicon carbide heaters........continued from page 1

SILICON CARBIDE ELEMENT SELECTION

The Silicon Carbide elements should be selected with the following guidelines:

• Calculate the heating power needed for the application.
• Calculate the number of elements needed per phase to supply this power keeping in mind the maximum limitation of the elements surface power dissipation W/cm². It is a good idea to de-rate this by approximately 10 to 20% as an operating safety margin.
• Based on the number of elements required, establish the configuration required. Ensure that each element is subject to the same operating condition (see Figure 2). In some cases it may be necessary to use an extra element or two (per phase), depending upon the element configuration, so as to keep the operating condition of all the elements the same.
• As the elements can change their resistance by a factor of 3 from "new" to "old", select the elements such that the voltage across them when "new" is approximately the mains voltage used divided by approximately 2 to 3. This allows for the aging of the element.

Figure 2

The Phase Angle Power Controller and the Supply Mains are required to be sized for the current drawn by the load when the elements are "new".

DATA FOR TYPICAL SILICON CARBIDE ELEMENT

Number E-204035

Diameter 20mm

Hot Zone Length 400mm

Cold Zone Length 350mm

Overall Length 1100mm

Hot Zone Surface Area 251mm²

Ohms 1.46 ohm

Nominal Volts 78V

Nominal Watts 4170W

Nominal Wattages at reduced surface loading power densities

Surface Loading Volts Watts

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