Circuit arrangement for the protection of thyristors of an invertor which operates in the pulsed mode

摘要

In order to protect thyristors of an invertor which operates in the pulsed mode against thermal overload a circuit arrangement is proposed which has first comparators (11, 12, 13) which are connected on the input side on the one hand to current transformers (1, 2, 3) which are in each case located in the output leads of the invertor and on the other hand to a first reference element (10) which emits a limit value corresponding to the instantaneous maximum-permissible current. On the output side, the comparators (11, 12, 13) are in each case connected via an integrator stage (20, 21, 22) to one input of second comparators, whose other input is connected to a common second reference element (19). The second reference element (19) emits a variable which is proportional to the maximum permissible current load during a time interval. The outputs of the second comparators (23, 24, 25) are connected to a common OR gate (17) which is connected via a re settable memory (18) to a switching element which interrupts the power supply to the invertor. <IMAGE>