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In TCR if the firing angle is changed from 90┬░ to 180┬░ the harmonics in ITCR __________________
increases
decreases
becomes zero
remains unchanged
increases
In a Thyristor Controlled Reactor (TCR), as the firing angle (╬▒) increases from 90┬░ towards 180┬░, the conduction period of the thyristors decreases. This reduction in the conduction interval causes the current waveform to deviate significantly from a pure sine wave, resulting in the generation of higher-order odd harmonics.
In a Thyristor Controlled Reactor (TCR), as the firing angle (╬▒) increases from 90┬░ towards 180┬░, the conduction period of the thyristors decreases. This reduction in the conduction interval causes the current waveform to deviate significantly from a pure sine wave, resulting in the generation of higher-order odd harmonics.
ITCRтАЛ(╬▒)=╧ЙLVтАЛ(1тИТ╧А2╬▒тАЛтИТ╧Аsin(2╬▒)тАЛ) тАФ Fundamental RMS current in TCR
InтАЛ=╧А╧ЙL4VтАЛ(n(n2тИТ1)sin(n╬▒)cos(╬▒)тИТncos(n╬▒)sin(╬▒)тАЛ) тАФ Harmonic current components
The TCR current is controlled by the firing angle ╬▒. At ╬▒=90┬░, the current is sinusoidal (full conduction). As ╬▒ moves towards 180┬░, the current becomes a 'chopped' sine wave. Because the waveform is no longer sinusoidal but retains odd-symmetry, it contains a significant amount of odd harmonics, with the magnitude of total harmonic distortion (THD) increasing as the conduction angle decreases.
At ╬▒=90┬░, current is purely sinusoidal and harmonics are theoretically zero.
TCRs generate odd harmonics (3rd, 5th, 7th, etc.).
Increasing ╬▒ results in a smaller conduction angle, increasing the non-linearity of the current waveform.
Filter circuits are usually employed to suppress the harmonic content generated by TCRs.
Stepless control of reactive power.
Fast response time compared to mechanical switching.
Generates significant harmonic distortion.
High switching losses at high frequencies.
Static Var Compensators (SVC).
Voltage stability improvement in transmission lines.
The range of ╬▒ for a TCR is typically between 90┬░ (full conduction) and 180┬░ (blocked state).
Option B is incorrect because reducing the conduction angle (increasing ╬▒) leads to more non-sinusoidal behavior, increasing harmonics.
Option C is incorrect as the current is only zero at ╬▒=180┬░, but in the transition range, harmonics are present.
A is correct тАФ increasing the firing angle reduces the conduction period of the thyristors, which makes the current waveform more non-sinusoidal and increases harmonic content.
Remember that any non-sinusoidal periodic waveform in power systems will inherently contain harmonics; the more 'chopped' or distorted the wave becomes, the higher the amplitude of these harmonics.