Performance analysis of the RC clampers in switching off no load arc furnace transformers
This paper presents an over-voltage attenuation performance analysis of RC clampers and surge arresters during transients caused by switching off a no load transformer applied to an arc furnace. A Brazilian Industry actual system was simulated using the Matlab/Simulink software. The simulation results indicate that the adequate use of RC clampers can reduce the arresters operations and practically eliminates the re-strikes and repetitive transient over-voltages when using vacuum circuit breakers to switch the arc furnace transformer.
Overvoltages due to switching off an unloaded transformer with a vacuum circuit breaker
When a vacuum breaker is used to disconnect an unloaded transformer, high overvoltages may result on the secondary side. The phenomena of current chopping and multiple reignitions after contact opening, shortly before current zero, play a significant role in generating these overvoltages, Furthermore, the transient recovery voltage (TRV) is also influenced by virtual current chopping which may lead to fast interruptions and reignitions. The paper reports on a vacuum breaker model implemented in the ATP-EMTP program. Simulations have been performed to determine overvoltages generated by the vacuum breaker, before and after suppression. Network elements were simulated by simplified models of limited complexity.
A new power measuring circuit using a bridge-connected magnetic circuit and another magnetic core
The authors describe the operating characteristics of an oscillating circuit using a bridge-connected magnetic circuit and another magnetic core. A square-shape output voltage is obtained in the oscillating circuit. The pulsewidth in positive and negative half cycles of output voltage changes with the current of the U-form core windings and with the signal voltage applied to the exciting windings. The mean value of the output voltage varies in proportion to the product of the current and the signal voltage. Utilizing this feature, an application of the oscillating circuit to a novel power measuring circuit of simple construction is presented. >