05/03/2020

Cycloconverter Interview Question Answer


1
State the function of the cycloconverter.


Function of the cycloconverter
  • The function of the cycloconverter is to convert constant voltage, constant frequency into variable voltage, and variable frequency without any intermediate stage.


2
Describe the Principle of operation of the cycloconverter.


Principle of cycloconverter
  • The cycloconverter consists of dual converter in which one converter works as positive converter whereas the other as the negative converter.
  • The firing angle of the both converter are adjusted such that

           αp + αn = π
           αp = Firing angle of positive converter
           αn = Firing angle of negative converter

3
Describe the effect on distortion on the output frequency of the cycloconverter?


As the output frequency increases, the distortion increases and vice versa.

4
Describe the different types of cycloconverter.


Types of cycloconverter
  • According to frequency : ( 1 ) Step up cycloconverter and          ( 2 ) Step down cycloconverter
  • According to output voltage : ( 1 ) Single phase to single phase – ( a ) Centre taped cycloconverter and ( b ) Bridge configuration cycloconverter ( 2 ) Single phase to three phase     ( 3 ) Three phase to three phase


5
Whether the cycloconverter is Phase commutated?


All types of cycloconverters are phase commutated except step up cycloconverter. The step up cycloconverter is forced commutated.

6
What is advantage of bridge configuration cycloconverter over centre taped cycloconverter?


The centre taped transformer is not requires in the bridge configuration cycloconverter.

7
Describe the function of the intergroup reactor in the cycloconverter?


Function of the intergroup reactor
  • The intergroup reactor is connected between midpoint of the positive converter and negative converter. 
  • It protect the supply from short circuited in the case of both converters are enabled.


8
What is meaning of the blocked mode cycloconverter?


Blocked mode cycloconverter
  • The cycloconverter consists of positive converter and negative converter. 
  • When the load voltage is positive, the positive converter operates whereas the negative converter is disabled. 
  • When the load voltage is negative, the negative converter operates whereas the positive converter is disabled. 
  • This is called as blocking mode operation of the cycloconverter.


9
Whether the blocking mode cycloconverter requires any intergroup reactor?


No

10
Describe the advantages and disadvantages of blocking mode over circulating current mode cycloconverter.


Advantages of blocking mode over circulating mode
  • No inter group reactor is necessary.
  • Low cost and size
  • Only one converter is in operation at all times therefore low losses and high efficiency.

Disadvantages of blocking mode over circulating mode
  • Distorting voltage and current waveform due to delay time.
  • The circulating current mode operation has smooth load voltage and fewer harmonic.
  • Harmonics in the output waveform
  • More control complexity due to current reversal.


11
Describe the advantages and disadvantages of the cycloconverter.


Advantages
  • Higher efficiency due to single stage conversion
  • All the cycloconverter works on line commutation except step up cycloconverter therefore it is not necessary for extra commutating components.
  • The power transfer from supply to load and vice versa at any power factor.
  • It can operate at distorted output waveform in the case of one SCR gets damaged.
  • It can generate high quality sinusoidal waveform particular at low frequency whereas the static inverter generate step wave voltage waveform at low frequency ( < 10 Hz ).

Disadvantages
  • Control circuit becomes complex due to higher number of SCRs.
  • Low power factor for low output voltage
  • The supply should be short circuited due to failure of commutation circuit.


12
State the applications of the cycloconverter.


Applications of the cycloconverter
  • Speed control of AC drives
  • Grinding mill drives
  • Induction heating
  • Variable frequency supply for shipyard or aircraft
  • Static VAr generation
  • HVDC transmission line


13
What is meaning of the hybrid operation of cycloconverter?


Hybrid operation
  • When the cycloconverter operates on both blocking as well as circulating current mode, it is called as hybrid operation.




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