Voltage Flicker Reduction with Svc in Steel Plant

The voltage flicker is main factor influencing the power quality and SVC is well-proven solution. The flicker reduction requires very short response time, according to the relation analysis between flicker improvement factor and response time. SVC has a fast open-loop control function to achieve effective voltage support. The fast algorithm of flicker reduction is presented here based on synchronization sequence decomposition and phaselocked, which makes it strong immunity to serious power environment. Filter parameters are optimized with good harmonic suppression function. Step response and site performance test are performed to show that this algorithm can get rapid response and better improvement of flicker reduction about 50%. This flicker reduction controller is enough effective and available in industrial application and makes good economic benefits. INTRODUCTION With increasing electricity load and its consumption, especially the impact of power load causes serious pollution of the power quality in the power distribution system [1]-[3]. This not only affects the quality of local power supply, and also influences nearby supply through power network coupling. Electric arc furnace is one of typical impact loads, which always brings non-period and asymmetrical short-circuit case. It is a complex and heavy load and is a large, unbalanced, and strongly fluctuating consumer of reactive power. These reactive power fluctuations which are very marked, especially at the beginning of the melting operation, lead to voltage drops and fluctuations that reduce the active power to the arc furnace and also to other loads connected to the same feeding bus bar. These results cause serious voltage fluctuation and flicker problem. The on-site measuring voltage and current curve of 30 ton EAF in operation is shown in the figure 1. Figure 1. Voltage and current measurment curve of EAF load THE MECHANICS OF SVCS SVCs traditionally comprise a combination of breaker switched Fixed Capacitor Banks that provide the capacitive reactive power and Thyristor Controlled Reactors (TCR) that provide the dynamically controlled inductive reactive power. Figure 2. Typical Configuration for SVC System. By controlling the firing angle on the thyristors, the current flowing in the TCR is rapidly controlled. The thyristors are very fast acting, which means that the reactive power output of the TCR can be changed in less than a cycle. A downside of the operation of the thyristors is the introduction of harmonic currents into the system. The fixed capacitors are designed to absorb the harmonic currents. Thus the SVC does not introduce unacceptable harmonic levels into the network. The rapid respond of SVC system makes the industrial grid achieve the good performance in operation. So SVC compensation device in the power supply system is indispensable and very important. Reasonable choice and design, configuration, must be implemented to minimize the network loss, to improve the quality of the grid. b.voltage curve