the voltage limits are not the dynistor and resistor R1.It is a question of terminology. In fact, don't be dynistor, the voltage on C1 would rise further, but the dynistor does not allow this to happen when you exceed 30 volts - discharge C1 at a control input of the thyristor. So the limitation circuit is not R1, and R1+VS2.
Why, after the diode bridge is a capacitor on 63В?For the same reason - the voltage there (with the correct operation of the circuit, of course) not supposed to reach 63 volts.
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