SCR Commutation Question & Answers November 2, 2022 By WatElectronics This article lists 50 SCR Commutation MCQs for engineering students. All the SCR Commutation Questions & Answers given below include a hint and a link wherever possible to the relevant topic. This is helpful for users who are preparing for their exams, interviews, or professionals who would like to brush up on the fundamentals of SCR Commutation. Transistors require voltages at the gate terminal to get turned ON and as the flow of voltage is stopped, it gets turned OFF. But this is not the case in thyristors or SCRs. Turning it ON require Gate voltage but as the voltage flow gets stopped still it will be in the mode of conduction. To turn it OFF i.e., to bring SCR from its forward mode of conduction to the forward state of blocking requires reducing anode currents below the level of holding currents. The process of turning OFF SCRs is referred to as Commutation. Commutation is about transferring currents between circuits. Directions of current can be reversed in windings as the commutators present in DC motors. Brush assembly consists of such commutators. Similarly in SCRs forward or the Anode currents are reduced to zero and it is turned Off. After it is OFF SCR can conduct forward voltages immediately. SCRs contain only OFF and ON states and also it doesn't have any control overload current and voltages. 1). What is SCR commutation? Process to Turn ON SCR Process to Turn OFF SCR Process to Make SCR Conduct Turn SCR into Conduction Mode None Hint 2). Turning OFF thyristor indicates that it is in ____________ mode. Forward Conduction Reverse Conduction Forward Blocking Reverse Blocking None Hint Read More about Turn OFF SCR 3). SCR in _____________ mode makes the gate to lose control? Forward Conduction Reverse Conduction Forward Blocking Reverse Blocking None Hint 4). External circuit used in SCR turn OFF referred to as ____________? Communication Circuit Commutation Circuit Conducting Circuit Conversion Circuit None Hint 5). What should be less than holding currents to turn OFF SCR? Anode Current Cathode Current Negative Current Reverse Current None Hint 6). Which voltage is applied around SCR to regain its forward mode of blocking from conduction? Anode Voltage Forward Voltage Reverse Voltage Zero Voltage None Hint 7). SCRs does not require ___________ to remain in ON state? Gate Voltage Negative Voltage Junction Voltage Threshold Voltage None Hint 8). Reverse voltages applied around SCR accelerates __________? Potential Resistance Recombination Regaining None Hint 9). How many states does any SCR have? Four Three Two One None Hint 10). SCRs does not have control over ____________? Load Voltage Load Current Gate Voltage a & b None Hint 11). Commutation is ___________ process? Simple Critical Easiest Convenient None Hint 12). What happens if SCR turns OFF? No Forward Currents Flow SCR does not Conduct Forward Currents Flow a & b None Hint 13). Reverse voltage applied in SCR Commutation referred to as __________? Anode Voltage Conduction Voltage Commutation Voltage Blocking Voltage None Hint 14) On what basis methods in commutations of SCR classified? Switching Synchronizing Recombining Biasing None Hint 15). What are the various methods of SCR commutation? Forced Commutation Artificial Commutation Natural Commutation a & c None Hint 16). What is turn OFF time of SCR? Time at Anode Current becomes Zero Time at Cathode Current becomes Zero Time at Anode Current becomes Maximum Time at Negative Currents are Maximum None Hint 17). What happens at SCRs turn OFF time? SCR Blocks Reverse Voltages SCR Conducts Reverse Voltages SCR Blocks Forward Voltages SCR Conducts Forward Voltages None Hint 18). What commutations have commutation voltages as its source of supply? Forced Commutation Artificial Commutation Natural Commutation a & c None Hint 19). ___________ occurs in AC circuitry only? Forced Commutation Artificial Commutation Natural Commutation a & c None Hint 20). If AC supplied to SCR, what happens at the end of each 'positive half' of the cycle? Thyristor Turn ON Thyristor Turns OFF Reverse Voltage Applied b & c None Hint 21). In how many categories, forced technique of commutations classified? Five Four Three Two None Hint 22). Natural Commutation method of SCR also referred to as__________? Source Commutation AC Line Commutation Class F Commutation All Mentioned Above None Hint 23). Natural Commutation of SCR can be made possible by ____________? Line Commutated Inverters Controlled Rectifiers AC Voltage Regulators All Mentioned Above None Hint 24). In Natural Commutation, tOFF should be _________ than supply half cycles duration. Lesser Greater Equal Large None Hint 25). What commutations takes place in DC circuitry? Forced Commutation Artificial Commutation Natural Commutation a & c None Hint SCR Commutation MCQ for Quiz 26). What requires the circuit externally to commutate SCR? Forced Commutation Artificial Commutation Natural Commutation a & c None Hint 27). Forward current in Forced commutation of SCRs are forcefully made __________? Maximum Highest Minimum Zero None Hint 28). What does commutating circuitry consists? Inductors Capacitors Resistors a & b None Hint 29). What causes the reverse voltages to applied around SCR? Commutating Components Resistors Active Components Passive Components None Hint 30). What are self-commutation classes in Forced Commutation? Class D & Class C Class C & Class B Class A & Class B Class B & Class E None Hint 31). Class A commutation occurs by __________? Load Resonation Source Resonation Voltage Resonation Supply Resonation None Hint 32). The source for voltage commutation is in _______ for Class A Commutation? Load Source Supply Load Resistor None Hint 33). Commutating components in Class A commutation connected in ___________with Load resistance? Series Parallel Either Series or Parallel Both Parallel and Series None Hint 34). ____________ RLC circuit of resonance selected in Self-commutation? Damped Over-damped Under-damped Excess Damped None Hint 35). Forward currents flow through SCR makes the capacitor ___________? Discharge Charged Up Charged Down Does not Affected None Hint SCR Commutation MCQ for Students 36). What determines the time to switch OFF SCR in Class A commutation? Resonant Frequency Cut-off Frequency Saturation Frequency Dynamic Frequency None Hint 37). Resonant Frequency of Class A commutation depends on ________? Commutation Components Load Resistance Source Resistance a & b None Hint 38). Class A method of commutation utilized in ___________? Low Frequency Operations High Frequency Operations Ultra High Frequency Operations Microwave Frequency Operations None Hint 39). SCR in Class B commutation has LC circuit connected in __________with Load? Series Parallel Either Series or Parallel Both Parallel and Series None Hint 40). In Class B of commutations, what happens if commutating currents are high than load currents? Thyristor Turn ON Thyristor Turns OFF Reverse Voltage Applied b & c None Hint 41). ____________ commutation is referred to as Complementary commutation? Class F Class E Class C Class A None Hint 42). ___________ gets connected to load serially in Class C Commutation? Main SCR Additional SCR Both Main & Complementary SCR Commutation Circuit None Hint 43). Frequencies below thousand Hertz use ___________ commutation? Class F Class B Class C Class A None Hint 44). SCRs with slower times of turning OFF are referred to as _________? Converter Grade SCRs Inverter Grade SCRs Retrograde SCRs Octa Grade SCRs None Hint 45). Externally applied pulse produces reverse voltages around SCR in __________ commutation? Class E Class B Class C Class A None Hint SCR Commutation MCQ for Interviews 46). What used to switch the capacitor charged in Class D of commutations? Main SCR Auxiliary SCR Both Main & Complementary SCR Commutation Circuit None Hint 47). Single-phase inverters use _________ commutation? Class F Class B Class C Class A None Hint 48). Chopper Circuits use _________ Commutation? Class F Class B Class C Class A None Hint 49). Series Inverters use ____________ Commutation? Class F Class E Class C Class A None Hint 50). Inverter and the chopper circuitry use _____________? Forced Commutation Artificial Commutation Natural Commutation a & c None Hint Please fill in the comment box below. Time's up
