Glass Industry Applications

Silicon Carbide is a semiconductor material, and has a much higher resistivity than metallic resistance materials. Room temperature resistivity is fairly high, and falls with increasing temperature to a minimum value at about 600-900°C. At elements temperature above 900° C. Resistivity increase with rising temperature, as shown in figure.
Therefore a constant power regulation is required with a V-type feed back to VxI transfer. On three-phase loads with Silicon Carbide it is suggested to use a feed back in VxI to obtain a constant power regulation. This is necessary to compensate for changes in the resistance value with the temperature and age of the elements. The value at the end of their use is 4 times the initial value. With the REVO C series use Burst Firing and power limit.
All silicon carbide elements gradually increase in resistance during their life in operation and the rate at which this occurs is affected by the following factors:
a) Element Specific Loading
b) Operating Temperature
c) Process Atmosphere
d) Mode of Operation (continuous or intermittent)
e) Power Supply Type used
f) Element Type
To optimize element life, the right type of element should be selected and the lowest specific loading consistent with the fournace design should be used. To compensate for the gradual increase in element resistance (ageing), a variable voltage power supply is usually provided, to enable the design power to be maintained throughout the life of the element.

This kind of heaters increase resistivity sharply with temperature.
The graph in this page show that at ambient temperature the resistance value is very low and increase its value up to 10 times.
To don’t oversize in current the Thyristor unit it’s necessary to limit the current to the load reducing the voltage with phase angle firing and current limit.
When the resistance value reach a setted value are possible two types of working method that can be selected from HMI:– Phase Angle plus current limit all the time long Or– Phase Angle plus current limit when the resistance is cold and transfering to Delayed Triggering if load is coupled with transformer.

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Select your load connection:
Pure resistive load
In this application REVO S Family up to 700A is normally used. Over this current we recommend the REVO C Family, up to 2100A. REVO C Family is also appreciated for communication, voltage compensation and burst firing, which prevents fluctuations in the mains voltage.
REVO PC is used to avoid Power Peak and Enegy Saving.
Load on secondary of transformer
Transformer have inrush current on start up. Special Tyristor Power Controller are required. REVO C with current limit option is normally used for 1PH loads. REVO C-3PH is used for three phase transformer.

Infrared radiation is commonly used for many industrial production processes. In secondary glass processing, infrared radiation is used for localized, fast and direct heating. This type of heating has a high penetrative efficiency, is easy to control, requires few costs, and is easy to install and maintain. From the point of view of lamp control we have the following cases:
Infrared lamps Medium and Long waveform
This type of heating elements are controlled as a normal resistance load, providing that the nominal supply voltage is used. If using medium waveform at a lower voltage than nominal, then this should be treated as short waveform load.
Infrared lamps Short waveform
Infrared Short Wave loads can be driven with different types of Firing: Single Cycle, Burst Firing and Phase Angle with Current Limit.
The graph demonstrates how the inrush current remains high for a longer period if we use Phase Angle plus Current limit, than with Single Cycle. Single Cycle technique is the most used to drive infrared short waveform. During the Off time the IRSW elements become cold (due to their low inertia) and when switched ON again there is a peak of current. This peak of current is a function of the number of Burst Firing Cycles, for this reason the Off time must be as short as possible to reduce this current peak. Phase Angle firing is not used because the supply voltage is normally less than nominal and therefore the elements never reach the working temperature.