# In a thyristor dc chopper, which type of commutation results in best performance

1.  Voltage commutation

2.  Current commutation

4.  Supply commutation

4

Explanation :
No Explanation available for this question

# A step down chopper is operated in the continuous conduction mode in steady state with a constant duty ratio D. If VD is the magnitude of the dc output voltage and VS is the magnitude of the dc input voltage, then ratio VD/VS is

1.  D

2.   1 – D

3.

4.

4

D

Explanation :
No Explanation available for this question

# A step down chopper operates from a dc voltage source VS, and feeds a dc motor armature with a back emf Eb. From oscilloscope traces, it is found that the current increases for time t0, falls to zero over time t1, and remains zero for time t0, in every chopping cycle. Then average dc voltage across the freewheeling diode is

1.

2.

3.

4.

4 Explanation :
No Explanation available for this question

# Figure given below shows a MOSFET with an integral body diode. It is employed as a power switching device in the ON and OFF states through appropriate control. The ON and OFF states of the switch are given on the VDS – IS plane by

1.

2.

3.

4.

4 Explanation :
No Explanation available for this question

# A chopper is employed to charge a battery as shown in the given figure. The charging current is 5 A. The duty ratio is 0.2. The chopper output voltage is also shown in the figure. The peak to peak ripple current in the charging current is

1.  0.48 A

2.  1.2 A

3.  2.4 A

4.   1 A

4

0.48 A

Explanation :
No Explanation available for this question

# A chopper has VS as the source voltage, R as the load resistance and α as the duty cycle. For this chopper, rmsf value of output voltage is

1.  Α VS

2.

3.

4.

4 Explanation :
No Explanation available for this question

# In dc-chopper, per unit ripple is maximum when duty cycle α is

1.  0.2

2.  0.5

3.  0.7

4.  none of these

4

0.5

Explanation :
No Explanation available for this question

# An inverter capable of supplying a balanced three-phase variable voltage, variable frequency output is feeding a three-phase induction motor rated for 50 Hz and 440 V. The stator winding resistances of the motor are negligibly small. During starting, the current in such can be avoided without sacrificing the starting torque by suitably applying

1.  low voltage at rated frequency

2.  low voltage keeping the V/I ratio constant

3.  rated voltage at low frequency

4.  rated voltage at rated frequency

4

rated voltage at rated frequency

Explanation :
No Explanation available for this question

# A voltage source inverter is normally employed when

1.  source inductance is large and load inductance is small

2.  source inductance is small and load inductance is large

3.  both source and load inductances are small

4.   both source and load inductances are large

4

source inductance is small and load inductance is large

Explanation :
No Explanation available for this question

# Consider the following statements : The diodes in a voltage source inverter (Mc Murry inverter) should be able to withstand a large voltage in the reverse direction. carry communicating current excess of load current. provide required reverse bias to the outgoing thyristor. feedback reactive current to the source. Of these statements

1.  1, 2 and 3 are correct

2.  1, 3 and 4 are correct

3.  2, 3 and 4 are correct

4.  1, 2 and 4 are correct

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