| 摘要 |
PURPOSE:To prevent the generation of an arc when a tap is changed as well as to prevent the oil filled in a change-over switch from contamination by a method wherein an intertap bridging current is suppressed through the intermediary of the voltage controlling element having the current blocking voltage range value higher than the instantaneous maximum voltage located between the two taps to be changed over. CONSTITUTION:When a tap-changing operation is started, a tap selector 24 is aparted from a voltage tap 4 at the time T2, and it comes in contact with a tap 5 at the time T3. As a semiconductor switch 28 still maintains an ON state, an intertap voltage corresponding to the potential difference between the voltage taps 4 and 5, is applied to a voltage limiting element 27. Then, as the limiting voltage of the voltage limiting element 27 is selected higher than the instantaneous maximum value of the intertap voltage, no interlayer bridging current runs through the intermediary of the voltage limiting element 27. Then, when a semiconductor switch 28 is turned OFF, the difference of potential at both ends of the semiconductor switch 28 is going to be boosted to the voltage of the voltage tap 4. However, as the limiting voltage of the voltage limiting element 26 or 27 is sufficiently small when compared with the tap voltage, it does not exceed the limiting voltage of the voltage limiting element 26. |
