Smart Thyristor Control of Power Supply on Electric Boosting Systems provides Potential Energy Savings
There are of course physical limitations to the interesting ongoing, commercial strive for higher glass furnace pull rates. One of those constraints is of course the maximum temperature that the crown refractory has to withstand, which has a direct correlation with the amount of energy that can be applied by combustion of fuel. To enable the input of more energy, without the side effects of higher superstructure refractory temperatures, there is another method which we all know as electrical boosting. Not only is boosting capable of applying potential amounts of energy to the melt it is also capable of providing better control of glass melt flow currents, and stirring effects, resulting in better and more efficient fining processes (especially in case of barrier boosting).
Electrical boosting is in principal a very efficient method of energy transfer especially as long as the system that provides the electrical power is built in line with the latest technical standards. The paper will describe how multiple zone SCR (silicon controlled rectifiers) boosting systems provide an optimum of power control and power distribution. It will illustrate how to avoid typical “hot spots” and provide the highest efficiency through the use of “Predictive Load Management” and burst firing (full sinus wave) methods. Historically SCR controlled boosting system used phase angle firing, also called phase cutting, which is a method of pulse width modulation (PWM) for power limiting, applied to AC voltages. The main disadvantage of this phase angle SCR firing method is that it courses relatively high reactive power content and harmonics. Only active power is capable to apply energy to the process, reactive power has to be seen as energy losses. Burst firing mode consists of supplying a series of whole mains cycles to the load. It works by modulating a SCR into and out of conduction only when the alternating current waveform passes thru its zero crossing. Burst firing minimizes the reactive power content and thereby it improves the SCR systems efficiency. To take away the possible disadvantage of unwanted simultaneous bursts of multiple boosting zones firing at the same time, which will course unwanted peak power demands, a predictive firing strategy is used to synchronize the zones’ firing and thereby optimize the total power consumption of such a multiple zone SCR system. It will also explain how different boosting system designs, using higher intermediary voltages and super compact water cooled transformers contribute in less energy losses, greater electrical power efficiency and power factor improvements, system standardization, more cost effective system designs and optimum stable glass melt flow patterns.
Water cooled transformers allow the units to be epoxy sealed allowing them to be located in environments have containment. With this and due to the ambient temperature of the water cooled transformer being the inlet water temperature, the water cooled transformers can be located closer to the load of the circuit reducing the losses in the system. These losses are both resistive and reactive and will decrease the power used and increase the power factor of the system.
http://www.hvg-dgg.de/fileadmin/dateien/veranstaltungen/ESG-2012-Flyer.pdf
