Q- In the below given voltage controller circuit
a) only the negative cycle can be controlled
b) only the positive cycle can be controlled
c) both the cycles can be controlled
d) none of the mentioned
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Answer: c
Explanation: As it consists of two SCRs, it is a full wave controller and both the half cycles can be controlled by varying their respective firing angles.
Q-In the below given voltage controller circuit
a) the positive half cycle at the load is same as the supply Vs
b) the negative half cycle at the load is same as the supply Vs
c) the positive and negative half cycles at the load are identical to the supply
d) none of the mentioned
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Answer: b
Explanation: As T1 is triggered at an angle α, the conduction in the positive have cycle will start at α. In the negative half cycle, the diode is forward biased and load is connected as it is to the supply.
Q-In the principle of phase control
a) the load is on for some cycles and off for some cycles
b) control is achieved by adjusting the firing angle of the devices
c) control is achieved by adjusting the number of on off cycles
d) control cannot be achieved
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Answer: b
Explanation: Switching devices is so operated that the load gets connected to ac source for a part of each half cycle.
Q-The AC voltage controllers are used in __________ applications.
a) power generation
b) electric heating
c) conveyor belt motion
d) power transmission
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Answer: b
Explanation: In electric heating, variable ac supply is needed. The devices are fired appropriately to apply enough temperature.
Q-In AC voltage controllers the
a) variable ac with fixed frequency is obtained
b) variable ac with variable frequency is obtained
c) variable dc with fixed frequency is obtained
d) variable dc with variable frequency is obtained
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Answer: a
Explanation: Voltage controllers convert the fixed ac voltage to variable ac by changing the values of the firing angle. The available ac obtained has the same fixed frequency as the input ac.
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