In a semi converter feeding a resistive load,a)the waveshapes of input...
The correct answer is option 'C': The waveshapes of input voltage and input current are similar only if the firing angle is zero.
Explanation:
A semi converter is a type of AC-DC converter that converts AC voltage to DC voltage. It consists of a diode and a thyristor connected in series. The diode allows the positive half-cycle of the input AC voltage to flow through, while the thyristor controls the flow of current during the negative half-cycle.
When the thyristor is triggered to conduct, it allows the current to flow through the load. The firing angle of the thyristor determines the point at which it starts conducting in each half-cycle of the input voltage. In a resistive load, the current is directly proportional to the voltage.
Let's analyze the different scenarios to understand why option 'C' is the correct answer:
1. Firing angle zero:
When the firing angle is zero, the thyristor conducts at the beginning of each half-cycle, resulting in the input voltage and current being in phase. The waveshapes of the input voltage and input current will be similar in terms of shape and amplitude.
2. Firing angle non-zero:
With a firing angle greater than zero, the thyristor starts conducting after a certain delay in each half-cycle. This delay causes a phase shift between the input voltage and current. The waveshapes of the input voltage and input current will not be similar, as they will have a time difference between their zero-crossing points.
3. Firing angle 180 degrees:
If the firing angle is set to 180 degrees, the thyristor will never conduct, and the converter will behave as a diode rectifier. In this case, the input voltage and current will be similar, but with a phase shift of 180 degrees.
Therefore, the waveshapes of the input voltage and input current in a semi converter feeding a resistive load are similar only if the firing angle is zero.
In a semi converter feeding a resistive load,a)the waveshapes of input...
Introduction:
In a semi converter, which is a type of AC-DC converter, a resistive load is connected to the output. The converter consists of thyristors that control the flow of current in the circuit. The firing angle refers to the delay between the triggering of the thyristor and the start of conduction.
Explanation:
The waveshapes of input voltage and input current in a semi converter can be described as follows:
a) The waveshapes of input voltage and input current are always similar:
This statement is not true. The waveshapes of input voltage and input current in a semi converter are not always similar. The firing angle determines the conduction period of the thyristor, and the current will flow only during this period. Therefore, the input current waveform will not be similar to the input voltage waveform.
b) The waveshapes of input voltage and input current can never be similar:
This statement is not true either. The waveshapes of input voltage and input current can be similar under certain conditions.
c) The waveshapes of input voltage and input current are similar only if the firing angle is zero:
This statement is correct. When the firing angle is zero, the thyristor conducts immediately after being triggered. In this case, the conduction period of the thyristor covers the entire half-cycle of the input voltage waveform. As a result, the waveshapes of the input voltage and input current will be similar.
d) The waveshapes of input voltage and input current are similar only if the firing angle is high:
This statement is not correct. When the firing angle is high, the thyristor conducts for a small portion of the input voltage waveform. The conduction period is shorter, and the current flows for a smaller duration. Therefore, the waveshapes of the input voltage and input current will not be similar.
Conclusion:
In a semi converter feeding a resistive load, the waveshapes of input voltage and input current are similar only if the firing angle is zero. This is because when the thyristor conducts for the entire half-cycle of the input voltage waveform, the current waveform is similar to the voltage waveform.
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