Power Electronics
A thyristor string is made of a no. of SCR connected in series and parallel. The string have volume and current of 11 KV and 4 KA. The voltage and current rating of available SCRs are 1800 V and 1000 A. For a string efficiency of 90 % let the number of SCRs in series and parallel are a and b respectively. Then the value of a and b will be

 6, 4.
 5, 7.
 4, 6.
  7, 5.

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Power Electronics
In forward blocking mode of a thyristor

  Junction J1 and J2 is in forward bias and J3 is in reverse bias.
  junction J2 is in reverse bias and J1, J3 is in forward bias.
  Junction J1, J3 is in reverse bias and J2 is in forward bias.
  junction J3 is in forward bias and J1, J2 is in reverse bias.

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Power Electronics
SCR will be turned off when anode current is

  < latching current but greater than holding current and gate signal is 0.
  both (A) and (B).
 less than holding current.
 < latching current but greater than holding current and gate signal is present.

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