1. For a 3-phase 6-pulse diode rectifier, has Vml as the maximum line voltage value on R load. The peak current through each diode is
a) Vml/2R
b) 2Vml/R
c) Vml/R
d) Insufficient Data
Explanation: Two diodes conduct at a time, constructing the equivalent circuit with supply, R & replacing the conducting diodes by S.C & non-conducting as O.C, the required value can be found out.
2. A 3-phase bridge rectifier, has the average output voltage as 286.48 V. Find the maximum value of line voltage
a) 100 V
b) 200 V
c) 300 V
d) 400 V
Explanation: Vo = 3Vml/π
Vml = (π x Vo)/3 = 300 V.
3. A 3-phase bridge rectifier charges a 240 V battery. The rectifier is given a 3-phase, 230 V supply. The current limiting resistance in series with the battery is of 8 Ω.
Find the average value of battery charging current.
a) 12.56 A
b) 8.82 A
c) 9.69 A
d) 6.54 A
Explanation: Vo = (3√2 x 230)/π = 310.56 V
Draw the battery charging circuit,
Vo = E + (Io x R)
Io = (Vo – E)/R = (310.56 – 240)/8.
4. A 3-phase bridge rectifier charges a 240-V battery. The rectifier is given a 3-phase 230 V supply. The current limiting resistance in series with the battery is 8 Ω.
Find the power delivered to the battery (Pdc).
a) Pdc = 2000 W
b) Pdc = 1226 W
c) Pdc = 2356 W
d) Pdc = 2116 W
Explanation: Vo = (3√2 x 230)/π = 310.56 V
Draw the battery charging circuit,
Vo = E + (Io x R)
Io = (Vo – E)/R = (310.56 – 240)/8 = 8.82A
Pdc = 240 x 8.82 = 2116 W.
5. In practice the output from the diode rectifier has
a) AC component only
b) DC component only
c) AC + DC component
d) None of the mentioned
Explanation: The output contents along with the DC components the AC harmonics which does no useful work & reduces the efficiency.
6. Choose the correct statement
a) The AC component in the output of rectifier does the useful work
b) The AC component in the output of rectifier increases the efficiency of the system
c) The AC component in the output of rectifier causes ohmic losses
d) The AC component in the output of rectifier does not affect the operation
Explanation: A rectifier is used to convert AC to DC. Lower the AC (Non-DC) components in the output lower are the ohmic losses.
7. An L filter is connected ________
a) in series
b) in parallel
c) in both series and parallel
d) none of the mentioned
Explanation: Inductor (L) has a very important property that the current through it cannot change rapidly. We can make use of this property by connecting it in series.
8. In case of an L filter connected with a rectifier in series with the load, it offers ________ impedance to ac whereas _______ resistance to dc respectively.
a) high, high
b) high, low
c) low, high
d) low, low
Explanation: It offers high impedance to AC such as the AC ripples do not pass through the load.
9. In case of a C filter, the AC is not allowed to pass to the load by
a) offering it high impedance
b) offering it low impedance
c) short circuiting the AC component
d) open circuiting the AC component
Explanation: AC ripples are not allowed to pass, by S.C the AC ripples as the C is always connected in parallel with the load.
10. A capacitor filter or C filter can be used in a rectifier by connecting it
a) in parallel with the load
b) in series with the load
c) in parallel with the supply
d) in series with the supply
Explanation: AC ripples are not allowed to pass, by S.C the AC ripples as the C is always connected in parallel with the load.