| 摘要 |
<p>876,415. Protective arrangements. WESTINGHOUSE ELECTRIC CORPORATION. Oct. 20, 1959 [Oct. 27, 1958], No. 35454/59. Class 38 (5). [Also in Group XL (c)] An undervoltage protective arrangement comprises means connected to each phase of a polyphase system for providing a signal voltage when the corresponding phase voltage is above a predetermined value, and transistor means controlled by the signal voltages for providing an output signal in the absence of any one of the signal voltages. In Fig. 1 there is connected to each phase voltage-dividing resistors 2, 3, a rectifier 4 and a potentiometer 5, and the resulting unidirectional voltage signals normally bias rectifiers 7 to their non-conducting condition so that the bias applied to the base of a transistor 11 from a source 8 causes the transistor to conduct. Under these conditions no voltage is applied across a capacitor 13. If the voltage of any phase falls below the predetermined value, the corresponding rectifier 7 is " unblocked " so that current can flow from the source 8 through the rectifier to earth causing the transistor to become non-conductive. The resulting output signal appearing at the collector of the transistor charges the capacitor 13 until the breakdown voltage of a Zener diode 14 is reached and a control device 15 is then operated. The device 15 may be a relay, a flip-flop circuit or an amplifier. Fig. 2 (not shown) illustrates a modified circuit in which a transistor is associated with each phase.</p> |
