| 摘要 |
<p>1328664 Protecting rectifying systems; protective arrangements UDYLITE CORP 16 Dec 1970 [22 Jan 1970] 59771/70 Headings H2F and H2K In a protection system for a static rectifier, excess current on the A.C. side is arranged to phase-back controlled rectifiers 41 ... 43 rapidly and to re-phase them gradually, the A.C. side being opened after a predetermined plurality of such phasing-back cycles if the gradually increasing current exceeds preset limits. As shown in Fig. 3, the magntiude of D.C. output from the rectifier diodes, is controlled by control of the conduction angle of antiparallel thyristors 41a ... 43b under control of a current-monitoring resistor 46. Over-current protection is achieved by monitoring the current on the A.C. side by current transformers 47a ... 47c and generating a control signal dependent on the peak current so as to turn off the thyristors 41a ... 43b for at least one cycle. Fig. 4 shows the peak current detector circuit and comprises diode bridges 49a ... 49c fed from the current transformers 47a ... 47c having load resistors 51 ... 53, respectively feeding transistors 54, 55, 56 which compare the resulting voltages with a reference voltage at the junction of resistors 63, 64. When the peak current in any phase is excessive, one of transistors 54 ... 56 is turned on, turning on transistor 72 which rapidly charges capacitor 76, providing a positive output at 77 via transistor 81, which is fed to the firing circuit (not shown) which turns off thyristors 41a ... 43b. Transistor 72 is now turned off and capacitor 76 discharges through resistor 75, gradually restoring the firing control signals from terminal 77. In the event of a persistent overcurrent fault, transistors 72 and 81 are kept cyclically turned on hence capacitor 87 becomes charged via transistor 84 and eventually increases the current in transistors 86 and 89 sufficiently to operate circuit-breaker 92 associated with contacts 45 on the A.C. side. Modification.-Fig. 1 (not shown) relates to a single phase circuit in which the diode rectifiers are replaced by phase-controlled thyristors and thyristors 41a ... 43b are omitted.</p> |
