question 2 b Consider a three phase rectifier circuit shown below and answer the
ID: 2082396 • Letter: Q
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question 2 b
Consider a three phase rectifier circuit shown below and answer the following questions. i. Please choose only one answer from the following and explain very briefly. A diode in a 3-phase rectifier conducts: a) One-half of the time period of the input, b) One-third of the time period of the input, c)One-fourth of the time period of the input, d) None of the above. ii. Suppose at some time, t the input line-to-line voltages are v_ab(t) = 240 V, v_bc(t) = 210 V, v_ac(t) = 260 V. Which diode(s) will be conducting at this time and why? iii. Please choose only one answer from the following and explain very briefly. In a 3-phase rectifier, given that the frequency of the input is 'f' Hz. the lowest frequency present in the output is: a) 2f, b) 4f, c) 6f, d) None of the above. e) Fill in the blank: Controlled three-phase rectifier inverter systems are used in HVDC transmission to allow .....Explanation / Answer
1) A Diode in a 3 phase rectifier conducts for one third of the time period of the input. Answer b is correct. Each diode will conduct for 120 degrees if the total time period of the input wave is 360 degrees. This is due to the fact that diode will remain forward biased for only 120 degrees as the output voltage of remaining diodes will reverse bias the first diode during the other time (i.e. from 120 to 360)
2) Diodes D1 and D2 will be conducting since maximum voltage of 260 V is applied across the third phase and also also due to which the other diodes are reverse biased. Diodes D1 and D2 will be forward biased and also this will reverse bias the other diodes.
3) In the three phase recumber of tifier, for input frequency of 'f' the output frequency will be 3f. Therefore the answer is None of the above.
4) Three phase rectifier inverters systenm are used in HVDC Transmission to accept distibution of high voltages from the source.,
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