| 摘要 |
<p>PURPOSE:To prevent the generation of a pulse voltage giving adverse effect onto the system by limiting a surge voltage caused between a feeding ground and a station office ground due to lightning or the like to a voltage lower than the usual operating voltage. CONSTITUTION:When a ground voltage Vg between a feeding ground S.E and a station office ground ST.E gets tentatively higher than a Zener voltage Vz of a constant voltage diode D1 or D2, a surge voltage is applied to a gate of a thyristor Th via a capacitor C, which is turned on. In this case, the ground voltage Vg is limited to a voltage nearly equal to the Zener voltage Vz. However, when a surge current is lost, since the ground voltage Vg is lower than the Zener voltage Vz, a gate current of the thyristor Th is zero and the thyristor Th is turned off. In this case, a series circuit Dn comprising plural diodes inserted between the gate and a cathode of the thyristor Th limits a voltage caused across a resistor R2 by the flowing surge current.</p> |
