# Electronics and Communication Engineering - Power Electronics

Exercise : Power Electronics - Section 2
46.
HVDC transmission systems generally use
12 pulse converters
6 pulse converters
3 pulse converters
either 12 or 6 pulse converters
Explanation:

To reduce ripple, 12 pulse converters are used in HVDC.

47.
A single phase semiconverter is feeding a highly inductive load. The circuit has a freewheeling diode across the load and firing angle is a. During one cycle of input voltage, the total duration of conduction of freewheeling diode is
a
2 a
4 a
0.5 a
Explanation:

Freewheeling diode conducts for a° in each half cycle.

48.
During forward blocking state of SCR, the voltage and current respectively are
high and high
low and low
high and low
low and high
Explanation:

Voltage is high but current is nearly zero.

49.
In a 3 phase full converter the average load current is 150 A. The average thyristor current is
150 A
75A
50 A
25 A
Explanation:

Each thyristor conducts for one-third of one cycle.

50.
The two modes of operation of three phase bridge inverters are known as
60° mode and 120° mode
90° mode and 120° mode
120° mode and 180° mode
120° mode and 240° mode