Exploring Power Electronics

Thyristor is a

• Current controlled device

• Voltage Controlled device

• Majority carrier controlled device

• Minority carrier controlled device

For protection of thyristor against high dv/dt which protection circuit is used

• Connecting an inductor in series with the thyristor

• Connecting a series RC(Snubber) circuit across the SCR

• Connecting a HRC fuse in series with the thyristor

• By removing the gate supply

What does the I²*t(Amp² -sec) rating of a thyristor specify

• The energy the thyristor can withstand in forward blocking state

• The energy which the thyristor can with stand before the fault is cleared

• The energy which the thyristor can withstand after the fault is cleared

• The power dissipated by the thyristor device

Which of the layer in a thyristor is the most lightly dopped

• Outer N layer

• Outer P layer

• Inner P layer

• Inner N layer

The reliability of a series connected SCR string is 60 percent , then the string efficiency will be

• 30 %

• 100%

• 40%

• 10%

Find the turn off time(milli sec) of a thyristor used as a Half wave controlled rectifier feeding resistive load. The AC supply frequency is 50 Hz

• 10 milli sec

• 20 milli sec

• 5 millisec

• 2.5 millisec

• 189.66V

• 192V

• 100V

• 250V

The turn off time for converter grade thyristor is

• between 40 to 100 nanoseconds

The main disadvantage of presence of source inductance in a single phase controlled AC-DC rectifier

• Average output voltage decreases

• Average output voltage remains same

• Average output voltage increases

• The firing angle increases

The thyristor is an

• fully controlled switch

• un controlled switch

• manual switch

• semi controlled switch