Test: Phase Controlled Rectifiers - 1 - Electrical Engineering (EE)

As the supply voltage is 400 sin 314t
V_m = 400 V,
Peak invesre voltage (PIV)

RMS value of current = 20 A 
Average value of current,

By using freewheeling diode, load performance becomes better because load current waveform is improved.
Whenever load voltage tends to go negative, freewheeling comes into play as a result of which ioaa current is transferred from main thyristor to freewheeling diode, allowing the thyristor to regain its forward blocking capability.
Hence, both assertion and reason are true but reason is not the correct explanation of assertion.

Power delivered to the load, for the same firing angle is more when freewheeling diode is used As volt-ampere input is almost the same witt and without a freewheeling diode, therefore the input power factor with use of freewheeling diode is improved.

The average output voltage for a single-phase full converter is

Maximum voltage across SCR in single-phase mid-point converter is 2V_m. Therefore, this converter can be design for a maximum voltage of

∴ Maximum average power that the mid-point converter can handle is

Circulating current gives rise to more losses in the converters, hence the efficiency and power factor are low. Thus, statement-1 is false.
In a non-circulating current type dual converter, the normal delay period of 10 to 20 ms is required while no delay period is required in circulating current type dual converter. Therefore, circulating current type dual converter is faster than non-circulating type dual converter. Thus, statement-2 is true.
As the dual converter with circulating current has to handle load current as well as circulating currents, therefore the thyristors are rated for higher currents. Hence statement-3 is false.

In case “four quadrant operation" is required without any mechanical changeover switch, two full converters can be connected back to back to the load circuit. Such an arrangement using two converters in antiparailel and connected to the same dc load is called a “dual converter."