| Abstrakt: |
Ac low voltage stabilizers with thyristor-based onload tap-changers are effective and cover 300 VA to 300 kVA applications. Among the solutions to reduce the internal short-circuit derived from the make-before-break changes, the multiwinding coil for years has proven to be reliable. This article shows a new operating mode of the coil that allows extra output voltages from every tap-switch using a magnetically coupled Nonius. The number of main taps is greatly reduced allowing, in a typical 10 MVA 34.5 kV line tap-changer, to save 33% of the cost of thyristors compared to the previous best solution without Nonius. In total, 29 voltage states can be obtained with only eight main taps and six auxiliary small Nonius taps per phase. Medium voltage stabilizers up to 36 MVA can be implemented using standard phase control thyristors with no series, nor parallel, association. Simulations and physical tests, controlled by digital signal processor, show that the new Nonius operating mode of the coil does not penalize the current rate of the switches, nor the flux of the coil core. Thus, magnetic-Nonius tap-changers achieve cost-effective stabilization with the fine regulation obtained by mechanical solutions with many taps. [ABSTRACT FROM AUTHOR] |
